CCNA (Cisco Certified Network Associate)

CCNA (Cisco Certified Network Associate)
CCNA
(Cisco Certified Network Associate)
(640-801).
© Copyright by CTF Services Limited 2005
All rights reserved worldwide. No part of this book may be reproduced or transmitted in
any form, or by any means, electronic or mechanical, including photocopying, recording,
or by any information storage and retrieval system, without the written permission of the
publisher, except where permitted by law.
Published by
CTF Services Limited, 19 Regent St, Timaru 8601, New Zealand
Author = Nick Thorne
Distributed by
www.ebooksctf.co.nz
Cisco CCNA (640-801).doc
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CCNA (Cisco Certified Network Associate) (640-801).
PREFACE.
Welcome to the exciting world of Cisco’s CCNA (Cisco Certified Network
Associate) certification. CCNA is the first of the Cisco Certification exams, and a
prerequisite for CCNP and CCIE. Cisco certification is a highly respected
International Certification in IT worldwide – and companies are very keen to
employ people who have Cisco Certifications.
CCNA is a great place to start with your Cisco certification. There are two parts
(2 exams):
 640-821 (Introduction to Cisco Networking Technologies
 640-811 (Interconnecting Cisco Network Devices)
Alternatively, you can sit one exam (640-801) which is a combination of the two.
I hope you enjoy doing this course, and will want to learn more after you finish.
This course is arranged as follows:
 14 Theory Chapters that include exercises and a glossary.
Please E-Mail us if you have any questions or comments.
Our E-Mail address is [email protected]
Please include (where possible) the Course Name and the Page Number (these
can be found on the footer of each page)
Enjoy the journey. We look forward to your continual success
Cisco CCNA (640-801).doc
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CONTENTS.
PART ONE:
Introduction to Cisco Technology (Exam 640-821)
CHAPTER 1
INTRODUCTION to CCNA.
CHAPTER 2
THE OPEN SYSTEM INTERCONNECTION MODEL (OSI).
CHAPTER 3
HARDWARE and the OSI MODEL.
CHAPTER 4
WIDE AREA NETWORK PROTOCOLS.
CHAPTER 5
TCP/IP.
CHAPTER 6
CISCO LAYER 2 SWITCHING.
CHAPTER 7
CISCO LAYER 3 ROUTING.
PART TWO:
Interconnecting Cisco Networking Devices (Exam 640-811)
CHAPTER 8
HARDWARE CONFIGURATION.
CHAPTER 9
CONFIGURING a CISCO SWITCH.
CHAPTER 10
CONFIGURING a CISCO ROUTER.
PART THREE: Sample Exams
CHAPTER 11
SAMPLE EXAM 801.821
CHAPTER 12
SAMPLE EXAM 801.811
CHAPTER 13
SAMPLE EXAM 801.801
PART FOUR:
Glossary
CHAPTER 14
GLOSSARY
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Majestic Mt Aoraki is an awe inspiring site.
My pledge my students:
To help you with your “Learning Climb” which is like scaling the heights of
Mt Aoraki (New Zealand’s highest peak).
There are times when you will be stretched beyond your comfort zone,
and there will be other days when the upward journey seems difficult (just
like bad weather on the mountain).
Aoraki is not the easiest challenge.
There are many easier, but less rewarding climbs.
Remember the words of Winston Churchill –
"Never, ever give up."
If you are willing to learn, and willing to work, then I am willing to
be your guide in your learning climb.
The view from the peak is even more awe inspiring than the view from the lake.
One day, you will reach your peak, if you follow the right path, and have the right
self belief.
Nick Thorne
Director of CTF Services
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PART ONE:
Introduction to Cisco Technology
(Exam 640.821)
CHAPTER ONE.
INTRODUCTION to CCNA
This chapter discusses the basics of Cisco certification exams, including a
description of the testing environment and a discussion of test-taking strategies.
Chapters 2 through 16 are designed to remind you of everything you'll need to
know in order to take—and pass—the CCNA 640-801 combined exam or the
CCNA 640-821 background and 640-811 configuration exams.
The three practice exams at the end should give you a reasonably accurate
assessment of your knowledge—and, yes, we've provided the answers and their
explanations. Read the E-Book and understand the material, and you'll stand a
very good chance of passing the test.
To completely prepare yourself for any Cisco test, we recommend that you begin
by taking the Self-Assessment that is included in this E-Book, immediately
following this introduction. The Self-Assessment tool will help you evaluate your
knowledge base against the requirements for a Cisco Certified Network
Associate under both ideal and real circumstances.
Based on what you learn from the Self-Assessment, you might decide to begin
your studies with some classroom training, some practice with configuration, or
some background reading. On the other hand, you might decide to pick up and
read one of the many study guides available from Cisco or third-party vendors on
certain topics. We also recommend that you supplement your study program with
visits to www.measureup.com for additional practice questions and simulations.
We also strongly recommend that you get some hands-on experience configuring
Cisco routers and switches. If you do not have access to the appropriate
equipment, you can log on to Cisco's Web site and practice with their
configuration simulator. Book learning is essential, but without a doubt, hands-on
experience is the best teacher of all!
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Taking a Certification Exam.
After you've prepared for your exam, you need to register with a testing center.
The combined exam (640-801) costs $US187.50, and if you don't pass, you can
retest for an additional $US187.50 for each additional try. Exams 640-811 (ICND)
and 640.821 (INTRO) cost $US100 each – and the same price for each retest.
Again, you can retest for either of these exams but you will have to pay a full
exam fee each time you retest. In the United States, Canada and Australasia,
tests are administered by Prometric and by VUE. Here's how you can contact
them:
 Prometric— You can sign up for a test through the company's Web site at
www.prometric.com.
 VUE— You can sign up for a test or get the phone numbers for local testing
centers through the Web at www.vue.com
To sign up for a test, you must possess a valid credit card or contact either
Prometric or VUE for mailing instructions to send a cheque. Only when payment
is verified or your check has cleared can you actually register for the test.
To schedule an exam, you need to call the number or visit either of the Web
pages at least one day in advance. To cancel or reschedule an exam, you must
call before 7 p.m. Pacific standard time the day before the scheduled test time (or
you might be charged, even if you don't show up to take the test). When you
want to schedule a test, you should have the following information ready:
 Your name, organization, and mailing address.
 Your Cisco test ID.
 The name and number of the exam you want to take.
 A method of payment. (As mentioned previously, a credit card is the most
convenient method, but alternate means can be arranged in advance, if
necessary.)
After you sign up for a test, you are told when and where the test is scheduled.
You should try to arrive at least 15 minutes early. You must supply two forms of
identification—one of which must be a photo ID—and sign a nondisclosure
agreement to be admitted into the testing room.
All Cisco exams are completely closed book. In fact, you are not permitted to
take anything with you into the testing area, but you are given a blank sheet of
paper and a pen (or in some cases an erasable plastic sheet and an erasable
pen). We suggest that you immediately write down on that sheet of paper all the
information you've memorized for the test. You are given some time to compose
yourself, record this information, and take a sample orientation exam before you
begin the real thing. I suggest that you take the orientation test before taking your
first exam.
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When you complete a Cisco certification exam, the software tells you
immediately whether you've passed or failed. If you need to retake an exam, you
have to schedule a new test with Prometric or VUE and pay another exam fee.
The first time you fail a test, you can retake the test 72 hours after the original.
After you pass the necessary set of exams, you are certified. Official certification
is normally granted after three to six weeks, so you shouldn't expect to get your
credentials overnight.
Many people believe that the benefits of CCNA certification go well beyond the
knowledge gained by the newly anointed members of this elite group. We're
starting to see more job listings that request or require applicants to have CCNA
and other certifications, and many individuals who complete Cisco certification
programs can qualify for increases in pay and/or responsibility.
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How to Prepare for an Exam.
Preparing for any Cisco-related test requires that you obtain and study materials
designed to provide comprehensive information about the product and its
capabilities that will appear on the specific exam for which you are preparing.
The following two sites can help you study and prepare:
 The Cisco Web site at www.cisco.com has an enormous amount of
material available to CCNA candidates. Configuration simulators, practice
tests, program updates, and career path guides are just a few of the
resources available at this Web site.
 Obtain CCNA exam simulations (640-821, 640-811 or 640-801 from
www.measureup.com (download for a fee is the quickest way)
In addition, you might find any or all of the following resources beneficial:
 Classroom training— Third-party training companies offer classroom
training on Cisco certifications. Although such training runs upward of
$350 per day in class, most of the individuals lucky enough to partake find
this training to be quite worthwhile. Cisco also offers classroom training
through vocational schools and community colleges. If you have a school
nearby that offers Cisco training, you should definitely explore the
programs available.
 Other publications— there's no shortage of materials available about
Cisco products and technologies.
What This E-Book Will Not Do
This book will not teach you everything you need to know about data
communications, or even about a given topic. Nor is this book an introduction to
computer technology. If you're new to Cisco products, technologies, and looking
for an initial preparation guide, check out www.quepublishing.com or
www.amazon.com, where you will find a whole sections dedicated to the Cisco
certifications. This book will review what you need to know before you take the
test, with the fundamental purpose dedicated to reviewing the information
needed on the CCNA certification exams.
This book uses a variety of teaching and memorization techniques to analyze the
exam-related topics and to provide you with ways to input, index, and retrieve
everything you'll need to know in order to pass the test. Once again, it is not an
introduction to data communications.
What This E-Book Is Designed To Do
This book is designed to be read as a pointer to the areas of knowledge you will
be tested on. In other words, you may want to read the book one time, just to get
an insight into how comprehensive your knowledge of computers is. The book is
also designed to be read shortly before you go for the actual test and to give you
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a distillation of the entire field of Cisco router and switch configuration basics in
as few pages as possible. We think you can use this book to get a sense of the
underlying context of any topic in the chapters.
We have drawn on material from Cisco's own listing of knowledge requirements,
from other preparation guides, and from the exams themselves. We've also
drawn from a battery of third-party test-preparation tools and technical Web sites
as well as from our own experience with Cisco technologies and the exam. Our
aim is to walk you through the knowledge you will need.
The CCNA exams make a basic assumption that you already have a strong
background of experience with local and wide area networking. On the other
hand, because the field is changing so quickly, no one can be a complete expert.
We have tried to demystify the jargon, acronyms, terms, and concepts. Also,
wherever we think you're likely to blur past an important concept, we have
defined the assumptions and premises behind that concept.
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Self-Assessment.
We included a Self-Assessment to help you evaluate your readiness to tackle the
Cisco Certified Network Associate program. It should also help you understand
what you need to master the topic of this book—namely, the combined Cisco
Certified Network Associate exam (640-801) or the two individual exams;
Introduction to Cisco Networking Devices (640-821) and Interconnecting Cisco
Network Devices (640-811). Before you tackle this Self-Assessment, however,
we will talk about the concerns you might face when pursuing a CCNA
certification and what an ideal candidate might look like.
Cisco Certified Network Associates in the Real World
In the next section, we describe an ideal CCNA candidate, knowing that only a
few actual candidates meet this ideal. In fact, our description of that ideal
candidate might seem downright scary. But take heart; although the
requirements for becoming a Cisco Certified Network Associate may seem
formidable, they are by no means impossible to meet. However, you should be
keenly aware that it does take time, requires some expense, and calls for a
substantial effort.
You can get all the real-world motivation you need from knowing that many
others have gone before you. You can follow in their footsteps. If you're willing to
tackle the process seriously and do what it takes to gain the necessary
experience and knowledge, you can take—and pass—the certification tests.
The Ideal Cisco Certified Network Associate Candidate
Just to give you some idea of what an ideal CCNA candidate is like, here are
some relevant statistics about the background and experience such an individual
might have. Don't worry if you don't meet these qualifications (or, indeed, if you
don't even come close) because this world is far from ideal, and where you fall
short is simply where you'll have more work to do. The ideal candidate will have
the following:
 Professional training and experience in networked Windows NT/ Windows
2000/Windows XP and or Unix operating systems.
 Experience cabling and troubleshooting local area networks.
 Experience installing and configuring WAN links.
 Hands-on experience configuring bridges, switches, and routers.
We believe that well under a quarter of all certification candidates meet these
requirements. In fact, most probably meet less than half of these requirements
(that is, at least when they begin the certification process). However, because all
those who have their certifications already survived this ordeal, you can survive
it, too—especially if you heed what this Self-Assessment can tell you about what
you already know and what you need to learn.
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Put Yourself to the Test
The following series of questions and observations is designed to help you figure
out how much work you'll face in pursuing CCNA certification and what kinds of
resources you can consult on your quest. Be absolutely honest in your answers,
or you'll end up wasting money on exams you're not ready to take. There is no
right or wrong answer, only steps along the path to certification. Only you can
decide where you really belong in the broad spectrum of aspiring candidates.
Two things should be clear from the outset, however:
 Even a modest background in computer science will be helpful.
 Hands-on experience with networked systems and technologies is an
essential ingredient for certification success.
Educational Background
1.
Have you ever taken any computer-related classes? (Yes or No)
If yes, proceed to question 2; if no, proceed to question 4.
2.
Have you taken any classes on networked Windows or the Unix operating
system? (Yes or No)
If yes, you probably have a good foundation for starting the CCNA
program. If the answer is no, consider some basic reading in this area. To
begin with, you should have a copy of Cisco's Internetworking
Technologies Handbook. This is the resource for the CCNA program and
many other Cisco certifications. In addition to the Internetworking
Technologies Handbook, there are so many good books it is hard to
recommend just one. Try stopping at one of the larger bookstores and
peruse the shelves. If you do not have a bookstore in your area, check out
Amazon.com. You should look for a practical book stressing networking
and that starts where your experience leaves off.
3.
Have you taken any networking concepts or technology classes? (Yes or
No)
If yes, you will probably be able to handle the networking terminology,
concepts, and technologies (but brace yourself for frequent departures
from normal usage). If you're rusty, or your answer is no, we recommend
you pick up a copy of Cisco Press's Network Sales and Services
Handbook by Matthew Castelli. Each company has its own language
(guess which one is used on the test). So, if you can find a book that uses
the same terms, you will find on the test you will be that much further
ahead.
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4.
Have you had experience cabling and troubleshooting networks? (Yes or
No)
If yes, you are one of the rare few with a golden future. If you answered
no, pick up a copy of Sybex's Cabling: The Complete Guide to Network
Wiring by David Groth and Jim McBee. Not only will this book provide a
good conceptual foundation for the CCNA but it will also give you a leg up
in the real world. Believe it or not, 70% of all network problems can be
traced to the wire.
Hands-On Experience
Another important key to success on all Cisco tests is hands-on experience. If we
leave you with only one realization after taking this Self-Assessment, it should be
that there's no substitute for time spent installing and configuring Cisco products.
5.
Have you installed, configured, and worked with Cisco routers and
switches? (Yes or No)
If yes, exam 640-821 and the configuration portion of exam 640-801
should be easy for you.
If you haven't worked with routers and switches, and do not have access
to Cisco equipment, hop on the Cisco Web site at www.cisco.com and
spend some time with the simulators. They are not as good as working
with the real thing, but they are better than nothing.
TIP:
You can obtain the exam objectives, practice questions, and other information
about Cisco exams from the Cisco Web site at www.cisco.com.
TIP:
If you have the funds or your employer will pay for it, consider taking a class at a
Cisco authorized training and education center. You can find the locations of
authorized centers at the Cisco Web site www.cisco.com
Testing Your Exam-Readiness
Whether you attend a formal class on a specific topic to get ready for an exam or
use written materials to study on your own, some preparation for the CCNA
exams is essential. At $US125 a try, pass or fail, you want to do everything you
can to pass on your first try. That's where studying comes in.
We have included several practice exam questions in each chapter and practice
exams for each of the exams, so if you don't score well on the chapter questions,
you can study more and then tackle the sample exams at the end of the book.
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TIP:
There is no better way to assess your test readiness than to take a good-quality
practice exam and pass with a score of 70% or better. We usually shoot for
80+%, just to leave room for the "weirdness factor" that sometimes shows up on
Cisco exams
One last note: We hope it makes sense to stress the importance of hands-on
experience in the context of the exams. As you review the material for the
exams, you'll realize that hands-on experience with Cisco equipment and/or
simulators is invaluable.
Onward, Through the Fog!
After you've assessed your readiness, undertaken the right background studies,
and obtained hands-on experience, you'll be ready to take a round of practice
exams. Start with the ones at the back of this book. When you score 70% or
better, you're ready to go after the real thing.
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Cisco Certification Exams.
Terms you'll need to understand:





Radio button
Check box
Exhibit
Multiple-choice/multiple-answer question formats
Process of elimination
Techniques you'll need to master:




Preparing to take a certification exam
Making the best use of the testing software
Time management
Question selection
This chapter is an introduction to the Cisco certification process and general
information on the taking of the authorized examination. We feel that having prior
knowledge of the method by which you will be tested will relax you and give you
comfort in knowing that you will be ready to tackle the task at hand.
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Cisco Certified Network Associate Career Certification
(CCNA) Changes
Recently, Cisco changed the requirements for their Cisco Certified Network
Associate (CCNA) designation to allow for a more flexible path to certification.
Candidates may still elect to take one exam (640-801) that will meet the
requirements for certification, or they can meet the certification requirements in
two steps with two exams (640-821 and 640-811). Many prefer the two-step
approach because it reduces the content in each exam to a more manageable
size.
The first half of this E-Book covers the material required by exam 640-821, and
the second part covers material required by exam 640-811. Together, the
sections cover everything required by exam 640-801. Therefore, this book can be
an effective guide no matter which path you choose. However, even if you select
the two-step approach, we strongly encourage you to read both sections of this
book prior to sitting for any of the exams. Our experience has shown that topics
that are confusing in one section will often become clear in the other.
Furthermore, familiarity with the entire scope of material can often make the
answer to a specific question more recognizable.
The exam names are as follows:
 Introduction to Cisco Networking Technologies (640-821). If you elect
the two-step approach, this will be the first exam you should take. It covers
local area networking, wide area networking, and relevant Cisco
equipment. The material is introductory level.
 Interconnecting Cisco Networking Devices (640-811). This is the
second exam of the two-step approach. It assumes you are familiar with
LAN/WAN technologies and moves directly into configuring and
monitoring Cisco routers and switches.
 Cisco Certified Network Associate (640-801). This exam essentially
combines exam 640-811 and exam 640-821. If you are recertifying or
have had experience configuring Cisco equipment, this is probably the
exam you want to take.
As long as we are making recommendations, here is one more. Monitor the
Cisco Web site as you prepare for the CCNA exams. Things change, and at
Cisco they change quickly. We made every effort to make this E-Book as up-todate as possible. However, without a doubt, something will change, and it may
affect the test, so be sure to monitor the Web site, which is located at
http://www.cisco.com.
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The Exam Situation.
Exam taking is not something that most people anticipate eagerly, no matter how
well prepared they are. For those of you who have already taken certification
exams, you will not find anything substantially different about taking the CCNA
exams.
Regardless of the number of exams you have completed, an understanding of
how to deal with the exam (how much time to spend on questions, the
environment you will be in, and so on) and the exam software that is provided will
help you to concentrate on the task at hand, which of course is passing the
exam. Also, experience has shown that mastering a few basic exam-taking skills
should help you to recognize some of the tricks and gotchas you are bound to
find in some of the exam questions.
Your first task is to find out where and when the exam is given and sign up for it.
This is a lot easier than it sounds. There are two organizations providing Cisco
certification testing:
 Vue Testing Service
www.vue.com
 Thompson Prometric
www.prometric.com
You can hop on their Web sites or call them directly. Either way, you will find a
nearby testing facility and a time you can take the test. You will need to provide a
credit card number because neither organization will test without payment up
front. The cost of each exam at time of publication is $145 U.S. dollars and is
subject to change. Now, the answer to your next three questions is "no.":
 No, you will not get a refund if you do not show up.
 No, you will not get a refund if you are late (they will not let you take the
test if you are late).
 Lastly, no, you will not get a refund if you do not pass the test, nor will you
get a discount on the retest.
Okay, sounds kind of harsh, doesn't it? Well, it is only harsh if you are late or
unprepared. Enough said?
When you arrive at the exam-testing center, you must sign in with an exam
coordinator and show two forms of identification, one of which must be a photo
ID. Please do not forget the photo ID. After you have signed in and your time slot
arrives, you will be asked to deposit any books, bags, or other items you brought
with you. Then, you will be escorted into a closed and hopefully quiet room.
Typically, the room will be furnished with one to half a dozen computers, and
each workstation will be separated from the others by dividers designed to keep
you from seeing what is happening on someone else's computer.
Before entering the exam room, you will be supplied with a pen or pencil and a
blank sheet of paper, or, in some cases, an erasable plastic sheet and an
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erasable felt-tip pen. Those are the only things you are allowed to take with you
into the test room. However, you are allowed to write any information you want
on both sides of this sheet once you enter the test room. Therefore, you might
want to quickly write down any facts or figures you might forget, such as IP
address ranges or configuration commands. When you are finished with the
examination, any materials that you had in the room will stay in the room for
exam confidentiality.
Most test rooms feature a wall with a large window or a security camera. This
permits the exam coordinator standing behind it to monitor the room, to prevent
exam takers from talking to one another, and to observe anything out of the
ordinary that might happen. The exam coordinator will have preloaded the
appropriate Cisco certification exam and you will be permitted to start as soon as
you are seated in front of the computer and ready to begin. The timer on the
exam does not start until you are ready to start, so do not rush anything.
All Cisco certification exams allow a certain maximum amount of time in which to
complete the work (this time is indicated on the exam by an on-screen
counter/clock, so you can check the time remaining whenever you like). The
number of questions and amount of time allotted for each exam will vary:
 Exam 640-821 will have 55–65 randomly selected questions and you may
take up to 90 minutes to complete the exam.
 Exam 640-811 consists of approximately 55–65 randomly selected
questions and you may take up to 60 minutes to complete the exam.
 Exam 640-801 will have 55–65 randomly selected questions and allow 90
minutes for completion.
All Cisco certification exams are computer-generated and use a multiple-choice,
multiple-answer question format. From time to time, you may be prompted to
enter actual configuration commands as if you were at the command-line
interface. It is important not to abbreviate the commands in any way when this
type of question is posed; the simulator is usually looking for one correct answer,
that being the full command. Although this may sound quite simple, the questions
are constructed not only to check your mastery of basic facts and figures about
Cisco router configuration, but also to require you to evaluate one or more sets of
circumstances or requirements. Often, you will be asked to give more than one
answer to a question. Likewise, you might be asked to select the best or most
effective solution to a problem from a range of choices, all of which are
technically correct. Taking the exam is quite an adventure, and it involves real
thinking. This book will show you what to expect and how to deal with the
potential problems and lead you on your way to being Cisco certified.
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Exam Layout and Design.
Some exam questions require you to select a single answer, whereas others ask
you to select multiple correct answers. The following multiple-choice question
requires you to select a single correct answer. Following the question is a brief
summary of each potential answer and why it is either right or wrong.
1.
What is the key piece of information on which routing decisions are
based?
A. Source Network layer address
B. Destination Network layer address
C. Source MAC address
D. Destination MAC address
A1:
Answer B is correct. The destination Network layer, or layer 3, address
is the protocol-specific address to which this piece of data is to be
delivered. The source Network layer address is the originating host and
plays no role in getting the information to the destination; therefore,
answer A is incorrect. The source and destination MAC addresses are
necessary for getting the data to the router or to the next hop address,
but they are not used in pathing decisions; therefore, answers C and D
are incorrect.
This sample question format corresponds closely to the Cisco certification exam
format—the only difference on the exam is that answer keys do not follow
questions; too bad. To select an answer, position the cursor over the radio button
next to the answer, and then click the mouse button to select the answer.
Now let us examine a question that requires choosing multiple answers. This
type of question provides check boxes rather than radio buttons for marking all
appropriate selections.
2.
Which of the following services exist at the Application layer of the
TCP/IP model? [Choose the three best answers]
A. SMTP
B. FTP
C. ICMP
D. ARP
E. TFTP
A2:
Answers A, B, and E are correct. SMTP, FTP, and TFTP all exist at the
Application layer of the TCP/IP model. Answer C is incorrect because
ICMP exists at the Internet layer of the TCP/IP model. Answer D is
incorrect because ARP exists at the Network Interface layer of the
TCP/IP model.
For this type of question, more than one answer is required. These particular
questions are scored as wrong unless all of the required selections are chosen.
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In other words, a partially correct answer does not result in partial credit when the
test is scored. For Question 2, you have to select the corresponding check boxes
next to items A, B, and E to obtain credit for a correct answer. These types of
questions can be tricky and involves some process of elimination.
These two basic types of questions can appear in many forms; they constitute
the foundation on which the entire Cisco certification exam questions rest. More
complex questions include so-called exhibits, which are usually network
scenarios, screen shots of output from the router, or diagrams. For some of these
questions, you will be asked to make a selection by clicking on a check box or
radio button on the screenshot itself. For others, you will be expected to use the
information displayed therein to guide your answer to the question. Familiarity
with the underlying utility is your key to choosing the correct answers.
Other questions involving exhibits use charts or network diagrams to help
document a workplace scenario that you will be asked to troubleshoot or
configure. Careful attention to such exhibits is the key to success. Be prepared to
toggle frequently between the exhibit and the question as you work.
Using Cisco's Exam Software Effectively.
The bad news is that unlike some exams by Cisco and other companies, these
particular exams do not allow you to mark questions for later review or skip
questions. In fact, the test engine will not let you proceed if you have not selected
an answer or if you have not chosen the correct number of answers.
With this in mind, time management is essential during the test. You cannot save
difficult or lengthy questions to do at the end of the exam. For this reason, it will
be helpful to monitor your progress by checking the clock periodically during the
test. The test has approximately 55–65 questions and allows anywhere from 60
to 90 minutes. Because time is tight, we suggested previously that you quickly
write down the quick facts before starting the exam. Believe me when I tell you
that every minute will count and the exams are too expensive to fail because of a
simple time management issue.
Cisco CCNA (640-801).doc
19
Exam-Taking Basics.
The most important advice about taking any exam is to read each and every
question carefully. Some questions are deliberately ambiguous, some use double
negatives, and others use terminology in incredibly precise ways. We may call
them tricky while Cisco will say that they are problem solving questions;
regardless, be aware.
Here are some suggestions for how to deal with the tendency to jump to an
answer too quickly:
 Make sure you read every word in the question. If you find yourself
jumping ahead impatiently, go back and start over, and be sure you have
selected the answer you wanted to select, especially in the exhibit style
questions.
 As you read, try to restate the question in your own terms. If you can do
this, you should be able to pick the correct answers much more easily.
 Try to deal with each question by thinking through what you know about
Cisco routers and their configuration—the characteristics, behaviors, facts,
and figures involved. By reviewing what you know (and what you have
written down on your information sheet), you will often recall or understand
things sufficiently to determine the answer to the question.
We are confident that if you are comfortable with the content of this book, then
you will be successful in your quest for certification.
Cisco CCNA (640-801).doc
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Question-Handling Strategies
Based on our experiences with certification exams, some interesting trends have
stuck out over the years. For questions that require a single answer, two or three
of the answers will usually be obviously incorrect, and two of the answers will be
plausible—of course, only one can be correct. Unless the answer leaps out at
you (if it does, reread the question to look for a trick; sometimes those are the
ones you are most likely to get wrong), begin the process of answering by
eliminating those answers that are most obviously wrong. To give you an idea of
what we are saying here, consider a question that asks you about forwarding
decisions of a switch. In all likelihood, two of the answers will be MAC address
and Network address. The other answers will probably be really odd. Do not get
too anxious and select the first one you see. Remember that a switch deals with
MAC addresses.
Numerous questions assume that the default behavior of a particular utility is in
effect. If you know the defaults and understand what they mean, this knowledge
will help you cut through many questions rather quickly and again save valuable
time for the less obvious questions.
As you work your way through the exam, another counter that Cisco thankfully
provides will come in handy—the number of questions completed and questions
outstanding. If you have fallen behind, use the last 5 minutes to guess your way
through the remaining questions. Remember, guessing is potentially more
valuable than not answering; blank answers are always wrong, but a guess may
turn out to be right. If you do not have a clue about any of the remaining
questions, pick answers at random. The important thing is to submit an exam for
scoring that has an answer for every question. We say this as a tip, however we
know that anyone who reads this book will never have to resort to that, right?
Cisco CCNA (640-801).doc
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Mastering the Inner Game.
In the final analysis, knowledge breeds confidence, and confidence breeds
success. If you study the materials in this book carefully and review all of the
exam questions at the end of each chapter, you should become aware of those
areas where additional learning and study are required.
Next, follow up by reading more materials about the subjects. The idea is to
become familiar enough with the concepts and situations you find in the sample
questions that you can reason your way through similar situations on a real
exam. If you know the material, you have every right to be confident that you can
pass the exam.
After you have worked your way through the book, take the practice exam at the
end of the book. This will provide a reality check and help you to identify areas
that you need to study further. Make sure that you follow up and review materials
related to the questions you miss on the practice exam before scheduling a real
exam. Take the real exam only when you have covered all of the ground and feel
comfortable with the whole scope of the practice exam.
If you take the practice exam and do not score at least 70% correct, you need
additional practice. Try to take as many practice exams as possible. If you have
exhausted the questions at the end of this book, search the Web; you will be
surprised at the number of questions available.
If you prepare seriously, you should do well. After all, if old guys like me can pass
the tests, you should have no problem. Good luck and let us know how you did!
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Part I: Introduction to Cisco Technology (Exam 640-821)
2 The Open Systems Interconnect Model (OSI)
3 Hardware and the OSI Model
4 Wide Area Network Protocols
5 TCP/IP
6 Cisco Layer 2 Switching
7 Cisco Layer 3 Routing
INTRODUCTION TO CISCO NETWORKING TECHNOLOGIES
(641-821)
The primary advantage of bridging is increased bandwidth available on a
segment because of the decreased number of devices in the collision domain.
Switches have the same basic functionality as bridges but they usually have
more ports. Each switch port is a separate collision domain, and each port
provides dedicated bandwidth.
Virtual local area networks (VLANs) can be used to make a group of switch ports
into a separate, isolated LAN. Routing is required for communication between
VLANs.
VLANs can function across multiple switches when they are connected by a trunk
connection. Inter-switch linking (ISL) is used to create a trunk connection
between Fast Ethernet ports on Cisco switches.
Switches make it possible to run Ethernet devices in full-duplex mode. In fullduplex mode, two devices share the Ethernet wire simultaneously and
exclusively, enabling faster throughput because very few collisions are possible.
Store-and-forward switching reads the entire frame before making a forwarding
decision; cut-through switching reads only the first six bytes—the destination
media access control (MAC) address—to make a forwarding decision. Store-andforward switching performs error checking; cut-through switching does not.
The primary advantages of routers are
 They allow you to connect dissimilar LANs
 They provide multiple paths to a destination network
 They allow the interconnection of large and complex networks
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Connection-oriented communication uses a nonpermanent path for data transfer.
It involves three steps: establish the connection, transfer the data, and terminate
the connection. A practical example of a connection-oriented communication
would be a walkie-talkie conversation where the connection has to be
established each time to the receiver by pressing a button, and once you are
finished talking you release the button until you want to talk again.
Connectionless communication uses a permanently established link. An example
of a connection-oriented protocol is TCP and an example of connectionless
communication protocol is UDP. Again, a practical example would be that of a
telephone conversation where a connection is made and maintained throughout
the duration of the call.
The layers of the OSI model are Application layer, Presentation layer, Session
layer, Transport layer, Network layer, Data Link layer, and Physical layer.
7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical
Encapsulation, or tunneling, takes frames from one network system and places
them inside frames from another network system.
The Presentation layer concerns itself with data representation, data encryption,
and data compression. It supports different protocols for text, data, sound, video,
graphics, and images, such as ASCII, MIDI, MPEG, GIF, and JPEG.
The Session layer establishes, manages, and terminates sessions between
applications. Network file system (NFS), structured query language (SQL), and
remote procedure calls (RPCs) are examples of Session layer protocols.
The Transport layer sits between the upper and lower layers of the OSI model. It
performs flow control by buffering, multiplexing, and parallelization. It provides
end-to-end data transport services by segmenting upper-layer applications,
establishing an end-to-end connection, sending segments from one end host to
another, and ensuring reliable data transport.
The primary functions of the Network layer of the OSI model are path
determination and packet switching. In addition, remember that the Network layer
is the domain of routing.
Cisco CCNA (640-801).doc
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The primary functions of the Data Link layer of the OSI model are:
 Allows the upper layers of the OSI model to work independently of the
physical media
 Performs physical hardware addressing
 Provides optional flow control
 Generates error notification
Convergence occurs when all routers in an internetwork agree on optimal routes.
A routing loop occurs when a packet bounces back and forth between two or
more routers.
Distance vector routing protocols send their entire routing tables to their
neighbors. Link state protocols send the state of their own interfaces to every
router in the internetwork.
Counting to infinity is a problem for distance vector routing protocols. It can be
eliminated or mitigated by using the following techniques: maximum hop count,
split horizon, route poisoning, and hold-down timers.
TCP provides a connection-oriented and reliable service to the applications that
use its services with the use of acknowledgments, sequence number checking,
error and duplication checking, and the TCP three-way handshake. User
Datagram Protocol (UDP) provides a connectionless and best-effort service to
the applications that use its services.
Well-known port numbers include:
 File Transfer Protocol (FTP) 21
 Telnet 23
 Simple Mail Transfer Protocol (SMTP) 25
 Domain Name System (DNS) 53
 TFTP 69
 Simple Network Management Protocol (SNMP) 161, 162
 HTTP 80
Address Resolution Protocol (ARP) maps a known IP address to a physical
address. Reverse Address Resolution Protocol (RARP) maps a known physical
address to a logical address.
Understand the basic concepts of IP addressing. Dotted-decimal notation is the
decimal representation of a 32-bit IP address. The dotted-decimal notation
represents the four octets of bits by performing binary-to-decimal conversion for
each octet and providing a decimal value for each octet.
Cisco CCNA (640-801).doc
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You should know the decimal representation of classes A, B, and C addresses
as well as the number of networks and nodes each supports as shown below:
 Class A: 1 through 126
 Class B: 128 through 191
 Class C: 192 through 223
You should be able to recognize the default mask for each class of IP address as
shown below:
 Class A: 255.0.0.0
 Class B: 255.255.0.0
 Class C: 255.255.255.0
The network number and broadcast address for a given subnet are the first and
last IP addresses, respectively. The range of usable IP addresses is all
addresses between the network number and broadcast address. In binary
format, the network number has all of the host bits of the address set to 0. The
broadcast address has all of the host bits set to 1.
You should know how to do subnetting tasks very quickly. It will save you
valuable time in the end.
The interface between the customer network and the WAN provider network
occurs between the data terminal equipment (DTE) and the data communication
equipment (DCE). DTE devices are usually routers. DCE devices are usually
modems, channel service units/data service units (CSUs/DSUs), and terminal
adapter/network terminations 1 (TA/NT1s).
Frame relay is a high-speed, packet-switching WAN protocol that operates at the
Data Link layer. It runs on nearly any type of serial interface, uses frame check
sequence (FCS) as its error-checking mechanism, and relies on a discard
eligibility bit for congestion management. A virtual circuit must connect two DTE
devices within a frame relay network. Permanent virtual circuits (PVCs) are more
widely used than switched virtual circuits (SVCs) in frame relay networks.
Data link connection identifier (DLCI) serves as the addressing scheme within a
frame relay network. Local Management Information (LMI) is a set of
enhancements to frame relay that was developed by Cisco, StrataCom, Northern
Telecom, and DEC. Cisco routers support LMI variations for American National
Standards Institute (ANSI), Q933a, and Cisco.
DLCIs are mapped to network layer addresses through inverse ARP or by using
the frame-relay map command.
Committed Information Rate (CIR) is the rate, in bits per second, at which data is
transferred across the frame relay network.
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Password Authentication Protocol (PAP) uses a two-way handshake to
authenticate Point-to-Point Protocol (PPP) connections and transmits
username/password information in clear text. Challenge Handshake
Authentication Protocol (CHAP) uses a three-way handshake and relies on
secret, encrypted passwords and unique IDs to authenticate PPP.
Integrated services digital network (ISDN) can be ordered as either basic rate
interface (BRI) or primary rate interface (PRI). ISDN functions represent devices
or hardware functions within ISDN. Reference points describe the logical
interfaces between functions.
ISDN can be used to add bandwidth for telecommuting, improve Internet
response time, carry multiple network layer protocols, and encapsulate other
WAN services.
Dial-on-demand routing (DDR) works with ISDN to establish and terminate
connections. It uses access lists to look for interesting traffic.
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Part II: Interconnecting Cisco Networking Devices (Exam
640-811)
8 Hardware Configuration
9 Configuring a Cisco Switch
10 Configuring a Cisco Router
INTERCONNECTING CISCO NETWORK DEVICES (640-811)
EXEC includes the following:
 Context-sensitive help for syntax checking, command prompting, and
keyword completion. Use the question mark (?) to activate contextsensitive help.
 Command history that provides a record of recent commands. Use the Up
and Down Arrow keys to scroll through the history list. Tab completes a
partially entered command.
 Enhanced editing that enables commands retrieved from the command
history to be changed quickly then re-executed. The terminal editing and
terminal no editing commands enable and disable enhanced editing.
 Use the Tab key to allow the router to complete commands after you get a
%incomplete command% message.
Examine the status of a router with the following commands: show version, show
memory, show protocols, show running-config (or write terminal), show startupconfig (or show configuration), show interfaces, and show flash.
The Cisco Discovery Protocol (CDP) displays summary information about directly
connected devices and operates at the Data Link layer. The show cdp neighbors
command displays ID, local and remote port, holdtime, platform, and capability
information. The show cdp entry <device id> command displays information
about a specific device, including all Layer 3 addresses and Internetwork
Operating System (IOS) versions.
The command to back up a router configuration file (copy a configuration file from
a router to a Trivial File Transfer Protocol [TFTP] server) is copy running-config
tftp. The command to restore a configuration file (copy a configuration file from a
TFTP server to a router) is copy tftp running-config.
Cisco CCNA (640-801).doc
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The commands to set the enable secret, console, and auxiliary passwords on a
router are as follows:
 Router(config)#enable password
 Router(config)#enable secret password
 Router(config)#line aux 0
 Router(config-line)#login
 Router(config-line)#password password
 Router(config)#line con 0
 Router(config-line)#login
 Router(config-line)#password password
 Router(config)#line vty 0 4
 Router(config-line)#login
 Router(config-line)#password password
To create a banner for a router and a description for an interface, use the banner
motd (message of the day) and description commands.
Router resource usage, bandwidth consumption, and update synchronization are
problems for link state routing protocols. They can be eliminated or reduced by
using the following techniques:
 Lengthening update frequency
 Exchanging route summaries
 Using time stamps or sequence numbers
Routing Information Protocol (RIP) can be configured on a router with the
following commands:
 Router (config)# router rip
 Router (config-router)# network <network>
 Interior Gateway Routing Protocol (IGRP) can be configured on a router
with the following commands:
 Router (config)# router igrp <autonomous system number>
 Router (config-router)# network <network>
The most important basic commands used to monitor IP with Cisco routers are
show ip interface, show ip protocol, and show ip route.
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A list of the important access list numeric identifiers follows:
 1 through 99: IP standard access list
 100 through 199: IP extended access list
 800 through 899: IPX standard access list
 900 through 999: IPX extended access list
 1000 through 1099 Service Advertisement: Protocols (SAP) access list
Two rules for applying a wildcard mask to an IP address are
 A 1 bit in the wildcard mask indicates that the corresponding bit in the IP
address can be ignored. Thus, the IP address bit can be either 1 or 0.
 A 0 in the wildcard mask indicates that the corresponding bit in the IP
address must be strictly followed. Thus, the value must be exactly the
same as specified in the IP address.
The difference in the capabilities of IP-extended access lists in comparison with
IP standard access lists is that standard access lists filter IP traffic based on
source IP address or address range. IP extended access lists filter traffic based
on source and destination addresses, ports, and many other fields.
Know that the last line of any access list is deny any any (implicit).
A single physical interface can be configured with several virtual subinterfaces.
Each subinterface can be configured with different addressing information.
Subinterfaces can be created and accessed using the serial interface number
followed by a period and a number (such as serial 0.78).
The commands to configure frame relay on a router are:
 Router (config)# encapsulation frame-relay cisco
 Router (config)# frame-relay lmi-type cisco
 Router (config)# interface serial 0
 Router (config-if)# frame-relay interface-dlci <dlci number>
The basic commands to monitor frame relay activity on a router are show framerelay pvc, show frame-relay lmi, show frame-relay map, and debug frame-relay
lmi.
The commands to configure PPP on a router are:
 Router (config)# username <name> password <password>
 Router (config)# interface serial 0
 Router (config-if)# encapsulation ppp
 Router (config-if)# ppp authentication chap
The basic commands to monitor PPP activity on a router are show interface and
debug ppp chap.
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The commands to configure ISDN on a router are:
 Router (config)# isdn switch-type <switch-type>
 Router (config)# dialer-list <dialer-group> protocol <protocol-name> permit
 Router (config-if)# interface bri 0
 Router (config-if)# encapsulation PPP
 Router (config-if)# dialer-group <number>
 Router (config-if)# dialer map <protocol> <next-hop address>
 name <hostname> speed <number> <dial-string>
 Router (config-if) dialer idle-timeout <seconds>
The basic commands to monitor ISDN and DDR activity on a router are show
controller bri, show interface bri, and show dialer.
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Cisco CCNA (640-801).doc
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Chapter 2.
The Open
Model (OSI)
Systems
Interconnect
Terms you'll need to understand:










Protocol Data Unit (PDU)
Encapsulation
De-encapsulation
Media Access Control address
Network address
Connection-oriented communication
Connectionless communications
Logical Link Control sub-layer (LLC)
Media Access Control sub-layer (MAC)
The seven OSI layers
Techniques you'll need to master:
 Understand the rationale behind the development of the OSI model
 Know the differences between connection-oriented and connectionless
communications
 Learn the functions of each layer and sub-layer in the OSI model
 Understand how the OSI model passes between network nodes
 Describe the five steps of encapsulation and de-encapsulation
The International Organization for Standardization (ISO) developed the Open
Systems Interconnection (OSI) reference model in 1984 for a host of reasons,
including:
 Increased interoperability between vendors
 Reduction of complex network operation to more easily understood pieces
 Simplification of future enhancements by keeping changes in one layer
from affecting other layers
 Providing a method or model to understand network and internetwork
communications
Cisco people can barely get out three sentences without referencing the OSI
model. They use it to define their products, troubleshoot communications
problems, and describe network operation, to name just a few. If you already
know the OSI model, feel free to skim this chapter, but do not skip it. This is one
of the areas where you definitely need to think "the Cisco way."
As we go through the layers of the OSI model, we will italicize terms that Cisco
uses in describing a particular layer. Pay attention to these italicized terms
Cisco CCNA (640-801).doc
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because you will run across them on the test and it is important you use them the
way Cisco uses them. In most cases, we will give you a definition of the term the
first time we use it, but in some cases we will defer the definition to a following
section where it is better defined in context. (Yes, we will tell you when that
occurs.)
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OSI Structure and Terms.
The OSI reference model breaks network communication into seven distinct
layers. These layers are then divided into upper layers and lower layers, and one
layer is further divided into two sub-layers. To further confuse things, the layers
are often referred to by their name, number, or a combination of both.
All of this can be a bit confusing, but if you keep the following points in mind,
eventually it will become clearer:
 The OSI model is conceptual; it does not describe how things actually
work.
 The OSI model is a universally accepted standard throughout the industry.
 The OSI model is a model based on theory, and it is an easier way to
understand the functions of data transfer.
Before we get too far into the model, let's clarify something:
The OSI model is a reference model. It provides a structure for organizing
functions of data communications, but does not necessarily address how those
functions are physically performed. A physical device like a "brouter" performs
both bridging and routing, which are functions found at different layers of the OSI
model.
Furthermore, the OSI model is not the only model used to describe data
communications. TCP/IP (Transmission Control Protocol/Internet Protocol) is the
most popular communication protocol in use today and it follows the Department
of Defense (DoD) four-layer model. So if you are thinking of the OSI model as the
blueprint for developing communications equipment, don't.
The OSI model provides a structure and organization for the functions of data
communications; it may or may not accurately describe the functions of a piece
of equipment or protocol. Also, not all companies describe the OSI model in the
same way. In fact, you can even find the model described differently within the
same company. Therefore, although you may already be familiar with the OSI
model, there will probably be some subtle differences between your
understanding of the model and the way Cisco defines the model. There is no
need to elaborate on which definition will be marked correct on the test, so
please do not skip this chapter.
The description of the OSI model in this chapter is consistent with what you will
find on the test. Pay particular attention to any areas that conflict with your
understanding of the model. If you are sure your understanding is correct,
remember the two rules for passing a Cisco certification exam:
Rule #1— Cisco's interpretation is correct.
Rule # 2— If Cisco's interpretation is not correct, see rule number one.
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Layer One, the Physical Layer.
The major function of this Physical layer is to place data on the network medium
and ensure that the medium is capable of carrying that data. The type and gauge
of wire, voltage levels, connectors, maximum distances, and other specifications
for the medium are all found at this layer. The Physical layer is the lowest layer in
the OSI model and as such is part of the OSI lower layers. (See Figure 1)
Figure 1. The seven layers of the OSI model.
TIP:
Cisco originally defined Layer 4 as a transitional layer between the upper and
lower layers of the OSI model. Later it was defined as part of the lower layers, as
described in many current texts. However, Cisco is moving away from making a
distinction between upper and lower layers, and this may well be reflected in the
current exam. Therefore, if you see a question on the exam asking where Layer
4 resides, the safest answer would be the lower layers. After all, the test you will
be taking has been extensively revised, so it should not define Layer 4 as
transitional, and if the test reflects Cisco's move away from making a distinction
between upper layer and lower layer groupings you will not get a question like
this at all.
Cisco CCNA (640-801).doc
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Figure 1 shows the seven layers of the OSI model as you will see it on the test.
The Application layer or Layer 7 (the layer names and numbers are used
interchangeably) is always at the top with the other layers listed in descending
order. This figure also breaks the OSI model into upper layers and lower layers.
Layer 2, the Data Link Layer
The Data Link layer or Layer 2 is responsible for low-level error-free
communication between two network devices or nodes. The Data Link layer is a
part of the lower layers and the only layer that is broken into sub-layers. Sublayers are always referred to by their name or initials and do not have a number.
The Media Access Control (MAC) sub-layer is the lower of these two sublayers, and is extremely important because it defines the addressing used by the
nodes of all networks. Every device or node attached to a network is required to
have a unique MAC address. Fortunately each device also requires a Network
Interface Card (NIC) to physically attach to a network and this is where the MAC
address resides. The address is actually burned into a chip on the NIC by the
manufacturer, which brings up an interesting question: How do the numerous
manufacturers of NICs know that the MAC address they are using is unique? The
MAC sub-layer specifies a way to ensure uniqueness. MAC addresses are 48
bits long and usually written as three groups of hexadecimal digits, like this:
081F.E453.5547
The first 24 bits (6 digits) is unique vendor code given to the manufacturer. The
last 24 bits (6 digits) is assigned by the manufacturer as a serial number. So long
as everybody plays by the rules, any complete MAC address will be unique.
The Logical Link Control (LLC) sub-layer rests on top of the MAC sub-layer
and provides the functionality required for connectionless and connectionoriented communication. LLC is the layer where protocol types are identified and
where they can be encapsulated.
Connection-oriented communication is much like a telephone circuit, which is set
up at the beginning of a conversation, maintained throughout the conversation,
and then released at the end of the conversation. Connectionless communication
is done on a frame-by-frame basis. Because each frame is autonomous, no link
is established or maintained. Connectionless communication is faster than
connection-oriented, but not quite as reliable. Each provides a way for upperlayer protocols to share transmission media, which is the main function of the
LLC layer.
Cisco CCNA (640-801).doc
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Layer 3, the Network Layer
Path determination and switching packets between networks are the primary
functions performed at Layer 3, which is also considered a lower layer. However,
before these functions can be performed, a structure of network addressing must
be established. Layer 2 already provides MAC addresses for every node on a
network, so why do we need another addressing function at Layer 3? The reason
is that MAC addressing uses a flat structure and is limited as to the number of
addresses available. If we tried to use MAC addresses for communication across
all networks, we would quickly run out of unique addresses or the addresses
themselves would have to be so large as to be unusable. A higher level of
addressing structure is clearly needed and that is provided by a Layer 3 routable
protocol. There are several routable protocols available, including Internet
Protocol (the IP portion of TCP/IP), Novell's Internet Packet Exchange (IPX), and
AppleTalk from Apple Computers. Each will provide a network addressing
scheme and use packets that have a field for network addresses.
Do not confuse routable protocols with routing protocols, which also operate at
Layer 3. Routable protocols such as IP, IPX, and AppleTalk provide a network
addressing format and a packet structure that includes a field for the network
address in addition to user data. Routing protocols are used by routers to
exchange administrative information. Routing protocols do not include user data.
Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) are
examples of some of the routing protocols we will discuss later.
Layer 4, the Transport Layer
The Transport layer is part of the lower layers of the OSI model. Establishing
end-to-end connection-oriented communications, dividing upper layer
communications into autonomous segments, and ensuring reliable data flow are
all services provided by the Transport layer.
Cisco CCNA (640-801).doc
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Layer 5, the Session Layer
The Session layer establishes, manages, and terminates communications by
coordinating service requests and responses between two or more stations.
Sun's Network File System (NFS) and IBM's Structured Query Language (SQL)
are representative of protocols used at the Session layer.
The upper layers—including Session, Presentation, and Application—provide
standardization for applications to communicate. The functions of getting the data
from one station to another are handled by the lower layers
Layer 6, the Presentation Layer
The Presentation layer ensures that information delivered to the Application layer
is readable and in the proper format. This includes the functions of data
encryption/decryption,
data
compression/decompression,
and
data
representation. Examples of data formats used at the Presentation layer include
ASCII, EBCDIC, MIDI, MPEG, JPEG, and GIF to name a few.
Layer 7, the Application Layer
The Application layer is at the top of the OSI stack and closest to user
applications. User applications providing communication functionality are
considered part of the Application layer. A word processing application by itself
would not be part of the Application layer. However, if the word processor
provided email capabilities, it would definitely be included in Layer 7.
TIP:
Be prepared to explain why the OSI model was developed, recognize the layers
by number and name, and lastly be able to list the major functions or services
provided at each layer. Remember that you are expected to answer questions
"the Cisco way," so use terms as presented here, which in all likelihood may be
slightly different than the way you learned the model.
Cisco CCNA (640-801).doc
39
The OSI Model in Operation.
There are four general rules that control the operation of the OSI model:
1. Data created at one layer must move down all layers below it before it can
be transmitted to a receiving station. If that data was created at the
Application layer, then it would move down through the six layers below it
prior to transmission. If the data was created in the form of a network
address at Layer 3, then it would move down through Layers 2 and 1 prior
to transmission.
2. When data arrives at the receiving station, it must move up to the layer
(peer layer) where it was created at the sending station. If the sending
station created the data at the Application layer, then the data would have
to move down through six layers of the sending station, be transmitted to
the receiving station, and then move up through six layers at the receiving
station until it arrived at the Application layer. If the data was generated at
Layer 3, then it would only move up to the peer layer (Layer 3) at the
receiving station.
3. A layer at the sending station can only communicate with its peer layer at
the receiving station and vice versa. In other words, a packet of data that
is assembled at the Network layer of the sending station can only be
disassembled by the Network layer of the receiving station.
4. Each layer provides services to the layer directly above it in the OSI stack.
The OSI stack was presented previously in reverse order because it seems to be
a little easier to understand that way. When you see the OSI stack in the real
world, it will always be ordered from Layer 7 down to Layer 1. If you have trouble
remembering the order, or the layers themselves, try saying; "All People Seem
To Need Data Processing." This should remind you of the layers and their order
from Layer 7 (Application) to Layer 1 (Physical).
Moving Through the OSI Model from the Application Layer
Let's follow a stream of data as it moves from the Application layer at a sending
station to the Application layer at a receiving station. Remember that for a user
application to be considered an application at Layer 7, it must require
communications to another node or station. Email is an excellent example of a
user application requiring communications, and as such is a Layer 7 application.
So, starting with an email message at Layer 7, the message is first passed to
Layer 6 (Presentation). Layer 6 encrypts and/or compresses the message as
required, and passes it to Layer 5 (Session).
Now the plot thickens. Starting with Layer 7, the message will move through five
steps of encapsulation. Encapsulation is the process of putting something inside
of something else, much like placing a letter in an envelope. Each layer from this
point on will add information to the message. The additional information includes
Cisco CCNA (640-801).doc
40
processing instructions for the same layer (Layer 5) at the receiving station. We
say the message is encapsulated because the additional information is added as
a header to the front of the message and often includes a trailer at the end of
the message. So in our case, the now encrypted and/or compressed message is
encapsulated at Layer 5 with information indicating that the message is part of a
single session. When information is encapsulated, it becomes a protocol data
unit (PDU). Each layer has its own PDU and the name of the PDU for Layer 5 is
"data".
TIP:
Occasionally, the name of a PDU will be the only clue you have as to the correct
answer for a question. You need to know protocol data units and the function of
each layer of the OSI model backwards and forwards. Sounds simple right? Well,
if the plot thickened in the previous paragraph, this is where it coagulates into an
ugly goo! People in the industry (including the fine folks at Cisco) cannot agree
on how to properly describe encapsulation in the OSI model.
Older Cisco instructors, and a majority of industry documentation, describe five
steps of encapsulation as we are doing here with the PDU for Layers 7 and 6
called an "information unit." We have seen test questions approach
encapsulation both ways. Of course, current Cisco instructional material, at least
the material we have seen, clarifies the matter by ignoring the issue completely.
So, what should you do on the test? Well, everybody agrees that encapsulation
occurs at Layers 5, 4, 3, 2, and 1. They also agree that the PDUs for these layers
are respectively "data", "segment", "packet", "frame", and "bits" (we will discuss
this in detail later).
The only areas of uncertainty are whether Layers 7 and 6 are encapsulating
levels, and should the protocol data units for these layers be called "data" or
"information unit". So here are our recommendations:
 Read the question very carefully. It will probably provide a clue.
 There are two ways of looking at encapsulation. Think before answering
any question dealing with encapsulation or PDUs.
 If there are equally correct responses for both views of encapsulation,
GUESS. A guess may not be right, but no answer is definitely wrong.
Figure 2 shows five levels of encapsulation with associated protocol data units
and OSI layers. There is still uncertainty as to whether Layers 6 and 7 should be
viewed as encapsulating with a protocol data unit of "data" or as not
encapsulating with a protocol data unit of "information unit".
Cisco CCNA (640-801).doc
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Figure 2. Protocol data units and encapsulation.
When a layer formats information from the layer above and adds additional
information, usually in the form of a header, the resulting assembly becomes a
"Protocol Data Unit" (see Figure 2). In effect, the data from the higher layer (the
letter) is encapsulated in data from the lower layer (the envelope). Layers 5
through 1 have PDUs with information specific to that layer. PDUs that are
specific to a given layer are why only peer layers (layers at the same level) at the
sending and receiving station can communicate. If all of this seems a bit murky,
read on and it should become clearer.
The Transport layer takes the Data PDU from the Session layer, adds additional
information as a header (encapsulating), and passes the resulting unit, now
called a Segment PDU, to the Network layer. The Network layer in turn
encapsulates the Segment into a Packet PDU with a logical source and
destination address, and then passes the Packet to the Data Link layer, which
encapsulates the Packet into a Frame with a physical source and destination
address. The Frame is then passed to the Physical layer where it is turned into a
Bits PDU and finally placed on the network medium.
If we have done everything right we will have used five steps of encapsulation,
while passing through seven layers, and yes you will need to keep all of this
straight for the test. Maybe Figure 3 will help.
Cisco CCNA (640-801).doc
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Figure 3. Data flow between network stations.
Figure 3 shows the flow of data between two network stations. Five levels of
encapsulation imply the PDUs for Layer 6 and Layer 7 would be an "information
unit". Seven levels of encapsulation would use "Data" as the PDU for Layers 5, 6,
and 7 and identify the upper two layers as encapsulating.
Packet Handling at the Receiving Station (Reversing the
Process)
Now that we have gone through seven layers and five steps of encapsulation,
what do you think happens at the receiving station? Right, everything happens in
reverse as the information flows up the OSI stack. The Physical layer of the
receiving station senses voltage on the medium, converts it into Bits, and strips
off any other signals placed there by the Physical layer of the sending station.
The remaining Frame moves up to the Data Link layer where the physical source
and destination address are removed and the resulting Packet is passed to the
Network layer. There the logical source and destination address are removed
and the remaining Segment is passed to the Session layer. Well, you get the
idea. The process of moving up the OSI stack at the destination node is called
de-encapsulation and when we finally get the information unit to the Application
layer of the receiving station, we have successfully passed data from one node to
another as described by the OSI model.
Cisco CCNA (640-801).doc
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Practice Exam Questions
1.
Which layers of the OSI model are included in the lower layers?
A. Application, Session, Presentation
B. Physical, Transport, Data Link, Network
C. Data link, Physical, Network
D. Session, Data Link, Physical
A1:
Answer B is correct. Over time Cisco has defined upper and lower
layers differently. At one time Layer 4 (Transport) was considered
transitional and not a part of either the upper or lower groupings. Then it
was included in the lower layers, and today Cisco is moving away from
the distinction of upper and lower layers entirely. Despite the changing
definitions, the safe answer is B. Answer A is incorrect because
Application, Session, and Presentation have always been a part of the
upper layers. D cannot be correct because again, Session is part of the
upper layers. C is incorrect because it would require Layer 4 to be
either transitional or part of the upper layers. Layer 4 has never been
considered one of the upper layers, and as this exam has just been
completely revised, the old definition of Layer 4 as transitional is highly
unlikely.
2.
Which layer uses the Segment as a Protocol Data Unit (PDU)?
A. Layer 3, Network
B. Layer 1, Physical
C. Layer 2, Data Link
D. Layer 4, Transport
A2:
Answer D is correct. The Transport layer uses the segment as its
Protocol Data Unit (PDU). The Physical layer uses Bits as a PDU while
the Data Link uses Frames and the Network layer uses Packets.
3.
Select three reasons why the industry uses a layered model.
A. A layered model allows developers to change the features of one
layer without affecting the other layers.
B. Interoperability is guaranteed because developers are required to
comply with the standards established by the OSI model.
C. Troubleshooting is easier if a layered model is used by all parties.
D. A layered model reduces the complexity of networking to more
manageable sub-layers.
A3:
Answers A, C, and D are correct. Answer B is incorrect because
compliance with the OSI model is voluntary. A developer can certainly
improve the ease of interoperability by adhering to the OSI model, but in
no way is a developer required to use the model.
Cisco CCNA (640-801).doc
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4.
Which of the following are upper layers of the OSI model? (Check all
correct answers.)
A. Layer 4
B. Network layer
C. Session layer
D. Presentation layer
A4:
Answers C and D are correct. The upper layers of the OSI model
include Layer 7 (Application), Layer 6 (Presentation), and Layer 5
(Session). Answer A is incorrect because Layer 4 (Transport) sits
between the upper layers and lower layers and is not considered a part
of either. Answer B is incorrect because the Network layer (Layer 3) is
part of the lower layers.
5.
Which of the following are routable protocols? (Check all correct
answers.)
A. Ethernet
B. AppleTalk
C. RIP (Routing Information Protocol)
D. IPX
E. TCP/IP
A5:
Answers B, D, and E are correct. IPX from Novell, AppleTalk from
Apple Computers, and TCP/IP all provide a place for a network address
in their packets. RIP is used by routers to exchange path information
and is considered a routing protocol, while Ethernet resides at Layer 2
and its frames have no place for a network address.
6.
Which of the following could be a legitimate Media Access Control
address?
A. 192.168.254.3
B. 3FA2.4756.F9A3
C. A5514
D. C1.3A.77.5B
A6:
Answer B is correct. A complete MAC address is composed of three
octets or 48 hexadecimal bits. Answers C and A are incorrect because
they do not have three octets or 48 bits. Answer A is a valid TCP/IP
address but again, does not have three octets or 48 hexadecimal bits
required by a MAC address.
Cisco CCNA (640-801).doc
45
7.
Which of the following are valid Protocol Data Units? (Check all correct
answers.)
A. Packet
B. Frame
C. Bits
D. Segment
A7:
All of the answers are correct. The PDU for Layer 3 (Network) is the
Packet. Frame is the PDU for Layer 2, Data Link. The Physical layer
(Layer 1) uses Bits for a PDU, and Layer 4 (Transport) uses the
Segment as a PDU.
8.
Where is encapsulation used in the OSI model?
A. All seven layers of the receiving station
B. At peer layers of both the sending station and receiving station
C. Only at the Network layer
D. At the sending station
A8:
Answer D is correct. Answers A and B are incorrect because deencapsulation is used at the receiving station. Although encapsulation is
used at the network layer of the sending station, it is also used at other
layers of the sending station and not at all at the receiving station.
9.
What is the serial number of a network interface card that has been
given an address of 0365.FF32.A673?
A. The serial number of a network interface card cannot be determined
from its address.
B. 0365
C. FF32.A673
D. 32A673
A9:
Answer D is correct. The last 24 bits (6 digits) of a network interface
card's MAC address are a unique number (serial number) assigned by
the manufacturer. The first 24 bits are a unique number assigned to the
manufacturer as the manufacturer's identifier.
Cisco CCNA (640-801).doc
46
10.
Which communications
operation?
A. OSI
B. TCP/IP
C. OSPF
D. DOD
A10:
Answer D is correct. The word "operation" is the key to this question.
Answer A, OSI, is certainly the most commonly used model, but it is a
theoretical model that rarely describes the actual operation of network
or network equipment. TCP/IP is the most commonly used routable
protocol, but it is not a communications model, which eliminates answer
B. OSPF is a routing protocol, which eliminates answer C. Answer D,
the Department of Defense Model (DoD), provided the specifications for
TCP/IP. As such, it is the model which closest approximates how
networks actually work today.
Cisco CCNA (640-801).doc
model
47
best
describes
today's
network
Cisco CCNA (640-801).doc
48
Chapter 3.
Hardware and the OSI Model
Terms you'll need to understand:













Hub
Bridge
Layer 2 switch
Router
Layer 3 switch
Repeater
Star topology
Bus topology
Coaxial cable
Twisted pair
Collision domain
Segment
CSMA/CD
Techniques you'll need to master:






Ethernet operation
Store and forward bridging
Network segmentation
Strengths and weaknesses of a star topology versus a bus topology
Identify hardware typical of Layers 1 through 3 of the OSI model
Understand the functions of and differences of bridges and Layer 2
switches
 Understand the operational differences and functions of Layer 1, 2, and 3
devices
When IBM released its first PC it started a veritable buying frenzy among
corporations. What separated the IBM PC from others of the time was not so
much technology as it was the IBM logo displayed prominently on the front of
each PC. The IBM logos made the PC acceptable for deployment in a corporate
environment, and deploy it they did! At the time, businesses were largely
dependent upon timesharing vendors to run ad hoc analysis and simulations.
The benefit of these real-time applications more than warranted the cost, which
in many cases exceeded $40,000 to $50,000 per month. A PC, however, could
often run the same application for a one-time cost of $6,000 to $12,000, making
deployment a foregone conclusion.
Cisco CCNA (640-801).doc
49
Why Are We Covering History?
You are probably asking yourself, why the history lesson? After all, Exam Crams
are supposed to be "the facts, only the facts, and nothing but the facts" right?
Well, there are really two reasons for this chapter. The first is that the CCNA
exam covers far more material than can be memorized. Many of the questions
will require you to determine the best answer based on your knowledge of how
and why things work the way they do. Taking some time now to review the
reasons behind the technology will not only pay big dividends at test time, but it
will also provide a contextual framework for discussing some pretty complex
equipment in the chapters to come. The second reason for the history lesson is
that it provides a way to remember the low-level properties affecting the design
and operation of today's equipment. The alternative is just listing electrical
properties, physical design limitations, and the physics behind network operation,
which can be drier than Oklahoma dirt. So put your feet up, relax, and let's go
back to the time of short sleeve white shirts and pocket protectors.
"Give a man a fish and he will surely want a steak" is a parable that holds true for
corporations as well as individuals, and it wasn't long before organizations were
demanding even more savings from PC installations. It didn't take a rocket
scientist to realize the major cost of PC deployment was in the peripherals, not
the PCs. A letter-quality printer could cost as much as a PC and a really big hard
drive, say 5MB, could exceed the cost of a PC. With the exception of running
back and forth with 5 1/2-inch diskettes (sneaker-net) those peripherals were unshareable and grossly underutilized. Ahh, if only peripherals could be shared,
think of the savings!
Cisco CCNA (640-801).doc
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Early Bus Networks (10BASE-5 and 10BASE-2).
About this time a consortium of manufacturers working at Xerox's PARC (Pacific
Area Research Center) released a really strange device called "Ethernet" that
would do exactly what was needed—namely share PC resources. Ethernet used
signaling that was well into the radio frequency spectrum and utilized a long
coaxial cable (up to 500 meters) as a medium to connect PCs and peripherals. A
coaxial cable consists of a single copper center conductor, covered by a
dielectric material (insulator), which in turn is covered by a braid of copper wire,
all of which is covered by a polyvinyl chloride (PVC) or Teflon jacket. (See Figure
1)
Figure 1. Coaxial Cable.
It is easy to see why installers preferred 10BASE-2 cable (right) over 10BASE-5
cable (left).
This type of cable is relatively immune to radio frequency interference from the
outside, and also does a good job of containing radio frequency signals on the
inside. Without these two properties, the cable would actually become a huge
antenna, with all kinds of nasty consequences.
However, there is a downside to this type of cable, and all other cables, including
fiber optics. The downside is that an impedance mismatch will reflect a signal. An
impedance mismatch occurs where the properties of the cable change. Joining a
cable to another with different properties will create an impedance mismatch.
Nicking a cable will also create a mismatch, or we can go for the biggest
mismatch of all and just whack the thing in half. Of course, all cables must end
one way or another, so to avoid the resulting impedance mismatch, both ends of
the coaxial cable were terminated with resistors (terminators). These terminators
Cisco CCNA (640-801).doc
51
would dissipate the electrical energy rather than reflect it (see Figure 2). This
assembly in its entirety is called a backbone or bus topology.
Figure 2. Bus topology.
A bus topology provides a single transmission cable called a bus. Network nodes
connecting to the bus share its transmission capacity. When coaxial cable is
used for the bus, a terminator (resistor) must be installed at each end to eliminate
reflections. Notice how the Ethernet symbol in the lower right resembles the bus
design.
The resulting reflections from a cut or nicked coaxial cable or fiber-optic cable
can bring an entire Ethernet system down. In fact, the nick or cut is located by
launching a signal down the cable and then timing the reflection. The device
used for this is called a Time Domain Reflectometer (TDR) for copper cable and
an Optical Time Domain Reflectometer for fiber optics. Both will provide the
distance from where the device is connected to the cut or nick by timing the
reflected signal.
The backbone cable was a really good idea but without a way to attach stations
or nodes it was useless, and this is where things got messy. Originally, nodes or
stations were attached to the bus by way of a tap, which physically pierced the
cable (see Figure 3).
Cisco CCNA (640-801).doc
52
Figure 3. 10BASE-5 taps.
These taps were quickly nicknamed vampire taps for obvious reasons, and the
name has stayed with them ever since.
The tap included a transceiver (transmitter/receiver) for signaling, and was
attached to the PC by an attachment unit interface (AUI) cable. The AUI cable
was often called a drop cable and closely resembled today's serial cable. The PC
itself was provided an interface card for attaching the drop cable and a piece of
software called a redirector that routed resource requests either to the
transceiver for transmission on the bus or to a locally attached resource, such as
a printer or hard disk.
We bet you are thinking that if a nick in the cable causes an impedance
mismatch and reflections, the pins of the vampire tap piercing the cable would
also cause reflections. Absolutely! That is why cable manufacturers marked
Ethernet cable with a ring every 2.5 meters. The natural resistance of the cable
could dampen the reflections from the pins, but it took 2.5 meters of cable to
provide adequate resistance. So each tap had to be at least 2.5 meters for
neighboring taps. That is why the cable was marked every 2.5 meters. If you
always placed your taps on the marks, reflection problems would be eliminated.
The layout of a single transmission medium, like a coaxial cable, providing
connectivity to a number of stations or nodes is referred to as a bus topology
(actually, the proper name for the backbone is bus but in practice the terms are
Cisco CCNA (640-801).doc
53
used interchangeably). Although multiple stations (Multiple Access) were
connected to the bus, only one signal could traverse the bus at any one time
(Baseband).
Multiple signals were eliminated because each of the network interfaces had a
circuit that sensed voltage on the bus (Carrier Sense). If a voltage or carrier was
present, the interface would delay transmission until the voltage again dropped to
zero. So, a situation where two or more signals ended up on the bus at the same
time would be highly unlikely.
In actual operation, having multiple signals on the bus can and does occur. Two
or more interfaces, sensing zero voltage, could, in fact, transmit at the same time
causing a collision on the bus. In fact, the stations did not necessarily have to
transmit at exactly the same time.
A signal takes time to move from one end of the bus to the other, so it is quite
possible a station on one end would transmit, not knowing there was already a
signal on the other end of the bus. Two or more signals on the bus would create
an over-voltage condition, which (you guessed it) would be sensed (Collision
Detection) by the same circuit that was monitoring the voltage in the first place.
When this occurred, the network interface would send a jam signal to busy out
the entire bus, wait for a random time period of no carrier or voltage on the bus,
and then retransmit the original signal. The random period of time was to prevent
a second collision when the two or more network interfaces that originally caused
the collision retransmit. Now you know why all Ethernets are categorized as
Carrier Sense, Multiple Access, Collision Detection (CSMA/CD) networks.
Pushing Distance Limitations (Repeaters)
The network we described previously was standardized as a 10BASE-5
(10Mbps, baseband, 500 meters) network and theoretically, if you stayed within
the standards, everything would work fine. However, it was a lot cheaper to
extend the bus a little over the 500 meter limit than to install a whole new bus,
and that is what many people did. The problem was that as a signal travels down
a medium, it loses a bit of its strength (attenuates) for every meter it travels. All
standards tend to be conservative so in most cases this did not create a major
problem. As people pushed the distance more and more, or used lower quality
materials, attenuation began to cause problems. So it was not long before a nifty
device called a repeater was developed to address signal attenuation.
A repeater is a Layer 1 (Physical layer) device installed between two segments of
a bus (the bus is actually cut and then reconnected through the repeater). A
repeater does not care about addresses, frames, packets, or any of the upperlayer protocols we have discussed. A repeater simply senses a voltage or signal
on one side, rebuilds and retimes the signal, and then sends it out the other side
(repeats). Do not make the assumption, however, that repeaters eliminate
Cisco CCNA (640-801).doc
54
distance restrictions. Like railroads, all networks operate on a foundation of
timing. It takes time for a signal to move down a cable and it takes even more
time for a repeater to rebuild, retime, and retransmit a signal. So long as we stay
within the established timing standards for our type of network, everything is fine.
If we exceed those standards, things get ugly fast (see Figure 4).
Figure 4. A segment is always a subset of a network (1). Both a repeater
and a bridge will divide a network into segments (2 & 3). However, only a
device with bridging functionality will create separate collision domains
as well as segments (3).
Cisco CCNA (640-801).doc
55
TIP:
More than one question will require knowing the difference between segment and
network. Segments are part of the same network and are formed as the result of
using a Layer 1 device such as a repeater or a Layer 2 device such as a bridge.
A network is a single entity that can include several segments, but as a whole
can be identified by a single Layer 3 address (see Figure 4).
Pushing Station Limitations (Bridges)
So now we have a flexible network that can be easily expanded and provides
sharing of expensive resources. The requirements have been met and everybody
is happy. Well, not quite. The economies generated by shared resources
provided a very real and tangible incentive for adding more stations to the
network, and that is exactly what companies did. After all, an Ethernet segment
could have as many as 1,024 nodes, which should be far more than anybody
would ever need. The problem was that very few organizations made it to 1,024
nodes. Degradation in response time and throughput became a problem long
before the magic number 1,024 was ever reached. Even more disturbing were
traffic studies that revealed an incredibly high number of collisions with very little
data transiting the network.
So what was happening? Well, it turns out that every node or station added to an
Ethernet network increases the probability of a collision. When a collision occurs,
the node interface sends out a jam signal that stops all transmission on the
network. The interface then waits for a random period of silence before
retransmitting the original frame of data. All of this takes time, and although the
network is busy, very little data is moving across the network. At some point the
network reaches its capacity of 10Mbps with the majority of that capacity used for
collision recovery. Depending on the type of traffic, that ceiling is usually reached
when approximately 4Mbps of data are moving across the network. Furthermore,
if we attempt to push even more data through a saturated Ethernet, the total
capacity available to data will decrease as the number of collisions increase. In
short, Ethernet has the remarkable characteristic of providing excess capacity
when you don't need it and reduced capacity when you do.
Well, no engineer can tolerate this kind of situation so it was not long before
another nifty device called a bridge was developed. A bridge allows you to cut
the Ethernet cable and then reattach it using the bridge. The bridge, like a
repeater, has two network interfaces, with each attached to a segment of the
cable. When a frame is launched on one segment (let's call it "A"), the bridge
copies the entire frame into a buffer, reads the source address and destination
address, and performs a Cyclical Redundancy Check (CRC) to ensure the
frame is complete and accurate.
Cisco CCNA (640-801).doc
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TIP:
A repeater segments an Ethernet network but does not create separate collision
domains. A bridge both segments a network and creates separate collision
domains (see Figure 4).
A Cyclical Redundancy Check is a number attached to the end of a frame that
was derived by running the digits of the frame through a specific computation.
The bridge performs the same computation and if the resulting number is equal
to the one stored in the CRC field, then the frame is considered accurate and
complete.
Because the bridge reads the entire frame, it is considered a Store and Forward
device. The bridge then writes the source address of the frame to a reference
table for segment "A" and checks to see if the destination address has also been
logged as a source address on segment "A". If the destination address is in fact
listed in the table, the bridge then knows that both the source and destination
addresses are on segment "A" and the frame is discarded. However, if the
destination address is not already listed in the table, the bridge assumes the
address must be located on segment "B" and the frame is passed on through the
second interface to segment "B". Of course the same thing is happening at the
interface for segment "B". Within a few seconds the bridge will have compiled
tables for the stations on both segments of the network and frames will either be
checked and passed or stopped and discarded based on destination address
and completeness of the frame. The ability of bridges to automatically build and
update network tables led many to call them learning bridges.
So, what did all of this really accomplish? First, traffic that is moving between
stations on the same segment stayed on that segment and did not tie up the
resources of the other segment. It was like gaining the capacity of two networks
with all of the benefits of a single network. Secondly, because a CRC was
performed on each frame needing transit across segments, only good frames
were actually passed. This effectively limits collisions to a single segment which
also frees the other segment to carry traffic. When a network is segmented with a
bridge, each of the segments is considered a separate collision domain (see
Figure 4). Prior to segmentation, the entire network was one collision domain.
We can also add multiple bridges, and create multiple collision domains, which
would greatly expand our capacity for additional stations.
TIP:
The collision domain is another one of those concepts that may not be
questioned directly, but will be at the core of several questions. Remember that a
collision domain is a group of nodes or stations that is connected in such a way
that if any two transmit at the same time, the resulting collision will affect the
entire group. A repeater is a Layer 1 device that will rebuild, retime, and
retransmit any voltage pattern down the wire. Although a repeater does break a
network into segments, it does not create separate collision domains. A bridge is
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a Layer 2 device that also segments a network, but because it stops collisions
from passing from one segment to the other, it does create separate collision
domains. If you understand collision domains to the point where you can easily
identify the problems of cut through switches discussed later in this chapter, then
you are ready.
So, with all of these benefits, was there a downside to using bridges? Of course,
it took time for a bridge to read and analyze each frame. Multiple bridges could
easily exceed the timing restrictions of a network. When this happened, stations
or entire segments at one end of the network would be completely unaware that
stations at the other end of the network had begun transmitting. The resulting
collisions storms could and did shut down entire networks. It was also possible to
accidentally create a loop with multiple bridges that would cause frames to
endlessly race around the loop until the network got so clogged it could no longer
function. The Spanning Tree Protocol (STP) was eventually developed so that
bridges could communicate with each other to determine which bridges would be
active and which would be held in reserve. This not only eliminated loops but
also allowed for redundancy in the network. Even with these drawbacks, the
bridge solved many more problems than it created and greatly advanced the
capabilities of networking.
Layer 3 Expansion (Routers)
However there was one limitation to bridges that could not be overcome. That
limitation had to do with scalability or size. I am sure you noticed how many times
the term "frame" was used in the previous paragraphs.
You already know that in the OSI model, "frame" is the PDU for Layer 2, and
Layer 2 is where MAC addresses are defined. So it would not be unreasonable to
assume that bridge functions were based on the MAC address of the network
interface attached to stations in the network. If you made that assumption you
are absolutely correct!
TIP:
You will likely get at least one "recall type" question relating directly to Protocol
Data Units (PDUs). However, many questions will use a PDU name without
calling attention to it, much like the way we used "frame" in the previous
paragraphs. This may be your only clue as to how to answer a specific question.
So be sure you can recognize PDU names, the layer of the OSI model where
they operate, and the functions of that layer. If you have been a bit sloppy with
the way you have applied PDU names in the past (all of us have), start
disciplining yourself right now to only use the name of a PDU in exact context of
its definition. That will go a long way toward making some of the test questions
intuitively obvious.
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Bridges are Layer 2 devices and the foundation of their operation is the MAC
address. You will probably also recall that MAC addresses have a problem with
scalability. Maintaining a unique address across many networks required going to
a higher level (Layer 3) where a logical network address was defined.
The MAC address is physical because it is burned into a chip on the network
interface. There is nothing virtual about it. What is on the chip is what you get
and only what you get, period. The network address is "logical" in that it is
derived from a routing protocol and assigned to a network. The network address
is not burned into a chip or physically attached to a device in any way. It is a part
of the software in use and can be readily changed. The concept is identical to
logical drives on a PC. You may have only one physical drive, but that drive
could, and usually is, configured as several logical drives.
The need for a different address scheme was not the only problem encountered
when data was passed across or between different networks. There was almost
always a change in media type, signaling requirements, and interface hardware.
The whole issue of network overhead also became a major problem. Network
stations needed a way to identify the addresses of other stations on the network.
One popular network software package accomplished this by having each station
broadcast its MAC address every three seconds. Now imagine you bridged the
networks of two remote corporate divisions over a 56Kb leased line that costs
$100,000 a month. With every station broadcasting its address across that link
every three seconds, how much real data could get through? Some other device
was clearly needed and that device was called a router.
Routers and bridges differ in that bridges use the MAC address (Layer 2) to
perform their functions while routers use the network address (Layer 3). That,
folks, "is the difference, the whole difference, and nothing but the difference"!
Routers rely on a routing protocol for the definition and establishment of network
addresses, and there is more than one protocol.
You are already familiar with at least one routing protocol named IP, which is a
part of TCP/IP and stands for Internet Protocol. Others include Novell's IPX and
Apple's AppleTalk. However, regardless of protocol, all routers fall into one of two
types: static or dynamic. Most smaller, single site applications use static routers.
A static router, or fixed configuration router, is initially configured by the user and
then it stays that way until the user goes back and manually changes the
configuration. Configuring a router is done using a command-line interface or a
Web-based interface developed by the manufacturer. Most static routers today
have a Web-based interface with very limited options so it will be easier for the
end user to configure. Simplicity is good in a static router because most of those
end users have little if any computer training. The good news is that once a static
router is configured it will merrily chug away forever, which is great for single
location with a stable network environment. The bad news is that every time the
environment changes, somebody has to physically change the operating
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parameters of the router. The really bad news is that if the environment changes
and the organization has multiple sites, somebody, hopefully not you, has to
reconfigure each router individually. This reconfiguration can usually be done
through a utility such as telnet, but in many cases requires a personal visit. So if
you get into a situation which uses static routers in multiple locations, keep your
bags packed and be prepared to make house calls.
The limitations of static routers were a major problem for big decentralized
companies with "big bucks" budgets, so it did not take long for a new type of
router to arrive on the scene. A router that could automatically adjust to changes
in the network environment, be configured and managed remotely, and provide
even more filtering capability would be perfect, and that folks is exactly what a
dynamic router or flexible configuration router does.
A major hurtle to development of dynamic routers was finding a way to make the
router aware of changes in the network and then provide it with a method for
determining the best route to a given address. Therefore, it should not be
surprising that the advent of dynamic routers coincided with advent of routing
protocols. A routing protocol provides a way for routers to exchange information
from their routing tables and then determine the best route to a network given
that information. Each protocol handles this function slightly differently, and each
has its own set of benefits and drawbacks. RIP (Routing Information Protocol)
and IGRP (Interior Gateway Routing Protocol) are examples of protocols that use
a distance vector algorithm for determining the best route. A distance vector
routing protocol requires each router to exchange information with its direct
neighbors. In this way, information travels from router by router throughout the
network. Some refer to this approach as "routing by rumor." OSPF (Open
Shortest Path First) and IS-IS (Intermediate System to Intermediate System) are
examples of protocols that use link state routing. Link state routing requires each
router to exchange information with every other router in the network. We will be
going into each of these approaches later. However, for now it is enough to know
that:
 Routable protocols provide a framework for addressing networks and a
structure (Packet) to carry user data across networks.
 Routing protocols provide a way for routers to exchange routing table data
and a method for determining the best rout to a given address.
Configuring a static router or fixed configuration router can be intimidating, and
they are designed for simplicity. Configuration of a dynamic router or flexible
configuration router can be downright otherworldly. Initial configuration of a
dynamic router is usually done through a command-line interface. However,
instead of having a dozen or so parameters like a static router, a dynamic router
can easily have thousands. The scary part is that not only do you have to find
where a parameter is set in a complex command-line interface, but you also have
to know the ramifications that setting will have on all of the other parameters that
interact with it. We are not trying to scare you here (well maybe a little). The real
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thing we want to get across is that setting up large dynamic routers is not a task
to be taken lightly. Becoming a Cisco Certified Network Associate (CCNA) is your
first step to joining the elite few who can really handle these complex systems.
We have arrived at a point where we have large bridged coaxial cable-based
networks connected by dynamic routers that are talking to each other and
keeping the whole system running like a top. In fact, the new coaxial cable
standard called 10BASE-2 (see Figure 1) largely replaced the bulky 10BASE-5
systems. 10BASE-2 installations use a much thinner coaxial cable and replaced
the dreaded vampire tap with a simple "T" connector (see Figure 5). So now
everybody should be ecstatic, right? The problems of installation were greatly
reduced, networks could be segmented with bridges to allow more users, and
routers provided long distance connectivity. What more could possibly be
needed? The answer is something other than coax.
Figure 5. 10BASE-2 Networking.
Figure 5 shows the "T" connector used to attach the bus to the station. The leg of
the "T" (facing forward) attaches to the interface card in the station, while the top
of the "T" provides a straight through connection for the cable.
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Development of 10BASE-T Wiring.
Even though 10BASE-2 made coaxial networks a little easier to work with, the
installations were still prone to catastrophic failures when the cable was nicked,
expensive to install and maintain, and difficult to work with. However, what was
the alternative? Well, a lot of people were asking why networking could not be
more like telephones and utilize a simple pair of wires. Actually, there were some
good reasons why networks could not use paired wires. Networks operated at
frequencies that were well into the radio spectrum. At those frequencies a pair of
wires would act like a giant antenna and radiate all over the place. The pair of
wires would also receive the signals of other radio frequency devices such as
fluorescent lights, monitors, and CPU units. All in all not a good thing, and the
very reason coaxial cable was used in the first place.
It would be nice to use paired wire in networks, but it just wasn't going to happen.
And it did not happen until a couple of engineering types figured out that if the
wires were twisted the radiation would be cancelled out, and that sending two
signals down the wires 180 degrees out of phase and then measuring the
difference would make other sources of radio frequency noise irrelevant.
The world of networking changed overnight. The twisted-pair cable required by
the new network was later standardized as Category 5 cable, and the whole
configuration was standardized as 10BASE-T (10 megahertz, base band, twisted
pair). Ethernet would remain a bus topology, but the coaxial cable that formed
the bus was shrunk to about a foot long. The taps, which included repeaters,
were attached to the bus at the factory, and each tap/repeater was terminated in
a modular receptacle much like the RJ-45 jack used by the telephone company.
The whole assembly was encased in a box with the receptacles mounted on the
outside. Today we call that box a hub (see Figure 6) and its use created a
topology called a star wired bus.
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Figure 6. A typical star wired bus topology.
The new topology was called a star wired bus because the bus remained within
the cabinetry of the hub. Of course, the coaxial cable was replaced by traces on
a printed circuit board, but the functionality of the bus was still there. 10BASE-T
cables radiated out from the hub to each station on the network, which is why it is
called "star wired."
The advent of the hub and 10BASE-T wiring eliminated most of the problems
inherent in a coaxial cable based bus network. The hub cabinetry protected the
physical bus, taps, and repeaters, eliminating damage from nicks, cuts, and leaky
tap connections. The difficult job of tapping into the bus was performed and
tested at the factory, which allowed field connections to be as simple as snapping
a Category 5 connector into the jack on the hub. That plagued coaxial cablebased networks. Because each station had a dedicated cable connecting it to a
repeater in the hub, individual cable runs could be up to 100 meters with cable
faults like cuts isolated to a single station. The dedicated hub connection also
isolated damage caused by cable faults to a single station. Lastly, when
compared to coaxial cable, 10BASE-T cable was extremely easy and
inexpensive to install.
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Enter the Switch
Today, Layer 1 repeaters and hubs and Layer 3 routers are used extensively in
networking, but we do not hear much about Layer 2 bridges. The reason is that
to a large extent bridges have been replaced. Remember that bridges read the
entire frame, check it for accuracy, and then forward or drop it depending on the
bridge's address tables. Also remember that this took time, and in highly
populated networks a store and forward device like the bridge could actually
become a bottleneck. So a couple of engineering types reasoned that to perform
a bridging function it was only necessary to read the source and destination
address from the beginning of the frame.
Based on this, a decision to drop or forward could be made and address tables
could be populated. Well, the cost of high-speed memory and processors had
dropped so much that rather than apply this approach to existing bridges and
gain an incremental speed advantage, it was decided that the time was right to
come out with a whole new class of device.
The new device read the source and destination address of the frame, populated
its bridging tables, and either passed or dropped the frame based on this
information. Sounds just like a bridge doesn't it? Well, here is where the plot
thickens. Instead of connecting just two segments, the new device connected six
or more. Forwarding a frame entailed building a virtual circuit between two
segments and then once the frame was passed the circuit could be used to
connect two other segments. Now if you had six segments you would only need
to run three virtual circuits to connect all of the segments. Or, if you only had one
virtual circuit, you could switch it between segments at three times LAN speed
and accomplish the same thing, namely a non-blocking switch. (See why the
high-speed processors and memory were needed?)
The term non-blocking means a device has the capacity to forward frames
between all possible segments at the same time. In short, if there is a bottleneck
in the network it won't be the switch. Each port connecting to a segment
maintained its own bridging table and when forwarding to another segment, the
frame was moved to what is often called the switching matrix. The switching
matrix established a virtual circuit between the two segments for just enough time
for the frame to transit the matrix to the destination segment. The device was
called a Layer 2 switch and its meteoric rise in popularity was only exceeded by a
plummet in popularity of the bridge.
But was there a downside to the capacity of the Layer 2 switch? At first the
answer appeared to be no, but then it was noticed that when a switched network
began to reach capacity, its operation became strangely erratic. It turned out the
key to the erratic behavior was linked to the very thing that gave the Layer 2
switch its awesome capacity and speed.
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The bridge read the entire frame and checked the CRC to ensure the frame was
complete and accurate before passing it on. The switch, however, only read the
source and destination address from the beginning of the frame. So only the first
few bytes of the frame would need to survive a collision to be passed on to
another segment. This did not become a problem until the segment approached
saturation. As the number of collisions rose, the switch would begin passing a
significant number of damaged frames. In essence, the switch was creating a
different collision domain every time it set up a virtual circuit and those collision
domains were changing so fast it was almost impossible to diagnose.
Most switches were put in environments that would never get close to saturation,
and in these situations they performed beautifully. Unfortunately, the erratic
performance usually occurred in large complex networks and it became enough
of a problem to prompt a redesign of the switch.
The first generation of switches became known as cut-through switches. The
second generation switch implemented a full store and forward operation
identical to the original bridges and accordingly was called a store and forward
switch. However, the store and forward technology came at the expense of
speed and price. So you could have a fast and cheap switch that would work fine
in some situations or a slow expensive switch that would work in all situations.
Seems like a compromise was needed, doesn't it? The compromise, which was
developed by Cisco, is called a fragment-free switch. A fragment-free switch
reads the first 64 bytes of the frame. Statistically, there is over a 90% chance the
remainder of the frame is intact if the first 64 bytes are. Cisco takes the best of all
three approaches by offering switches that can be configured to operate in any of
the three modes.
Everybody knows a switch is a Layer 2 device. A switch works with MAC
addresses so the only thing it could be is a Layer 2 device. However, Cisco has a
very popular line of products that apply the fast switching matrix of Layer 2 to the
routing of packets at Layer 3. Do you know what Cisco calls those devices? You
guessed it, "switches"!
Terms are always evolving at Cisco. The term "switch," in this case, is moving
from the generic name of a device to the description of a technology. So be
careful of the assumptions you bring with you to the test. Your assumptions are
probably not wrong, but they may be very different from the way Cisco sees the
world. Enough said?
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Token Passing Topologies.
We have already covered a lot in this chapter, but we really can't move on
without going over one last network technology. That technology is Token Ring, a
la IBM. You will not see Token Ring questions on the CCNA test per se, but you
will need to know about wide area token passing networks, and they are easier to
understand if you know about their LAN counterparts.
The Token Ring network architecture has become closely identified with IBM and
for good reason. Way back in 1972, IBM announced a Token Ring control
method for LANs which was remarkably similar to one developed by a Mr.
Willemjin. The IBM announcement sparked a host of license and patent disputes
which resulted in Mr. Willemjin becoming a very rich man. This was an apt
beginning for IBM's long and painful journey into local area networking.
At the time, IBM owned the global mainframe computing market with few able to
compete. Others realized there was no way to take on IBM in the mainframe
market, but the new interest in distributed computing held promise. Distributed
computing utilized small computers tied together in a network and offered user
groups a level of control not possible in mainframe computing. Although IBM now
had the Token Ring Architecture free and clear sitting on a back shelf, it viewed
the whole trend toward distributed computing as detrimental to continued
expansion of the mainframe and as a result nothing happened for more than 10
years. Finally, as IBM watched companies like Digital, Network General, and
Wang grow, they decided to act. Of course IBM was not about to legitimize the
technologies these upstart companies were using, so something different was
needed, and something that was really different had been sitting on a back shelf
for over 10 years.
Token Ring was released as a whole new architecture, including special cables,
hardware, and even different terms to describe its operation. The concept was
sold to large IT departments and while the DP guys didn't especially like the idea,
it did give them a way to offer additional services to the user communities and
reclaim some of the budget and control they had lost to distributed processing.
Token ring, as the name implies, used a ring structure where each node was
physically attached to its neighbors (see Figure 8). Data passes from one node to
the next in a counterclockwise direction as it traverses the ring. Typically, IBM
type one cable was used, which was not much smaller than the old 10BAEE-5
cable. The cable contained heavy gauge twisted pairs of wires wrapped in one or
more shields of high density braid and foil. The cable was terminated in a
complex connector measuring about 2 inches square, which would allow cables
to be joined together or attached to devices such as Multi-Station Access Units
(MSAU), which provided a central attachment point for the ring.
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Figure 8. The Token in Token Ring
The operation of the ring began when the first station was attached or started.
That station would send a query over to the ring to see if any other stations were
active. If not, the station would assume the role of active monitor and release a
token (see Figure 7).
Figure 7. Token Ring Operation.
Unlike a bus where each node attaches to one shared cable, Token Ring uses a
dedicated cable between neighboring nodes. Data must flow from the upstream
neighbor, through a dedicated cable to the next downstream node. That node
repeats the frame and launches it on the cable attaching it to its next downstream
node.
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A token is like a data frame but only has a starting delimiter, access control field,
and ending delimiter (see Figure 8). It is used to notify a node that it may now
send data. If the node has data to send, it will change the ID bit in the token to
indicate it is now a data frame, attach the data, and transmit the data frame to the
next downstream neighbor (see Figures 7, 8 and 9). If there is no data to
transmit, the token will be repeated and sent to the next downstream neighbor as
is.
Figure 9. The Token Ring Data frame.
If the frame is not addressed to the next downstream neighbor, that node
retransmits it to the next downstream node. This process continues until the data
frame arrives at the node it is addressed to. That node reads the data frame,
changes the frame status field to indicate the frame has been received, and then
retransmits the updated frame on to the sending node. At the sending node, the
frame is compared to the frame that was sent originally, and if they are identical
the node releases a token frame and the whole process starts over. This is the
process followed by the standard 4 megabit Token Ring network. A variation of
this process has the receiving station release a token after it has read, updated,
and sent the original data frame. This variation is called "early token release" and
it is used in 16 megabit Token Ring networks. No matter what variation is in use,
there can only be one token on the ring at any one time. I think you can see why
IBM liked this approach: no collisions, few if any retransmits, and control of cable
quality.
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So, what happens when a cable is severed? That should stop ring operation,
shouldn't it? Well, yes, but even in this situation Token Ring offers some benefits
over Ethernet. Each node monitors traffic from its nearest active upstream
neighbor (NAUN). There is always a Token frame or Data frame on the ring so
there is always traffic. When traffic stops coming from a node's NAUN, that node
goes into beacon mode, which will be heard and repeated by all of the
downstream nodes. The presence of a beacon on a ring indicates the ring has
stopped functioning and a serious problem exists. In addition, the address of the
beaconing node indicates the problem is somewhere between it and its NAUN.
So not only are serious problems reported, but their location is also identified.
Neat eh?
Traffic that moves from one ring to another is handled somewhat differently than
Ethernet. To begin with, each ring is a network in its own right, so routing and
bridging get a bit mixed. This is one architecture that definitely stretches the OSI
model. Notice the routing information field, which is a part of the data frame in
Figure 9. When data is bridged in a Token Ring environment, a process called
source route bridging is used. The initiating node sends several special frames to
the receiving node, which echoes the frames back. The route of the frame that
returns first is added to the routing information frame of the data frame and the
frame is sent to the bridge.
Although Token Ring is a Layer 2 architecture, its frame has a large field for
routing information. In this case, the field is used to store instructions for source
route bridging.
The bridge does not have to check any tables or determine any routes because
the routing instructions are included with the data frame in the routing information
field; hence, source route bridging. Data frames can also be encapsulated in
routable protocols and follow a more traditional way of moving between
networks. This procedure would have to be adopted if the route passed across
non-Token Ring networks.
This is as far as we are going to go in Token Ring. Introducing Token Ring earlier
in the chapter would have really confused things; we mention it here because it
will help build a foundation for things to come. On the test, assume you are
dealing with Ethernet unless told otherwise. Speaking of tests, why don't you try
the following questions and see how you do?
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Exam Prep Questions
1.
Your company has upgraded all of its hubs to switches. One of the
switches appears to be working overly hard, with its overall traffic
indicator lit continuously, as are the port lights. Your boss is afraid there
is a bottleneck and dispatches you with one of the company's $70,000
protocol analyzers to diagnose the problem. However, when you plug
the analyzer into an open port, it reports extremely light and sporadic
traffic. What, if anything, is the problem?
A. Indicator lights on networking equipment are notoriously inaccurate.
If the protocol analyzer reports light traffic then the switch is well below
capacity and there is no problem.
B. The switch probably has address filtering activated on the analyzer's
port. Deactivating the filtering option will give the analyzer access to all
traffic.
C. Switches build virtual circuits between two ports. If the analyzer's
port is not part of the current circuit, it will not see activity.
D. There is no problem. Unlike a hub, activity lights on a switch should
be on constantly.
A1:
Answer C is correct. Okay, this was a nasty way to start because we
haven't even mentioned activity lights and protocol analyzers.
Nevertheless, if you know how a switch works, it should not be hard to
deduce the answer. Switches do create virtual circuits between two
ports. If a port were not part of the circuit, it would not be aware of the
activity. That makes answer C a likely candidate. Activity indicator lights
are not accurate, but if every port's indicator is lit constantly, that switch
has to be really working. Therefore, A is probably not correct. Filtering
sounds good, but even without filtering, the analyzer would still only see
activity broadcast or addressed to its port. That rules out B as a correct
answer. Lastly, if every port activity indicator is constantly lit, it would be
logical to assume there is activity. A switch only connects two ports at a
time, so having all of the port activity lights continually on is probably
not normal. Therefore D is questionable as a correct answer.
2.
Which type of switch can create multiple temporary collision domains
when segments approach saturation?
A. Cut-through switches
B. Non-blocking switches
C. Switches running in fragment-free mode
D. Store-and-forward switches
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A2:
Answer A is correct. Early cut-through switches read the source and
destination addresses and dropped or forwarded frames based on that
information alone. As segments approached saturation and the number
of collisions escalated, cut-through switches could and did pass the
remains of collisions provided the source and destination address fields
survived intact. When this occurred, both segments would essentially
be in the same collision domain connected by the switch. Answer B is
incorrect because non-blocking means the switch has the capacity to
switch frames between all segments at the same time. Answer C could
be correct because a fragment-free switch examines only the first 64
bytes of the frame. However, it has been shown that if the first 64 bytes
of a frame are correct then there is greater than a 90% chance the
remainder of the frame is also correct, so few if any damaged frames
would be passed. Answer D is incorrect because a store-and-forward
switch is the only type of switch that will stop all damaged frames by
performing a cyclical redundancy check (CRC) prior to passing the
frame on.
3.
How did the 10BASE-T standard put an end to the cumbersome bus
structure of early Ethernets?
A. 10BASE-T eliminated the bus in favor of star wiring that was far less
expensive and more reliable.
B. Networks using the 10BASE-T standard moved the signaling
frequency below the radio spectrum so common twisted-pair wire could
be used.
C. A network using the 10BASE-T standard was far more reliable than a
bus network because severing a cable only brought down a segment of
the network.
D. A network using the 10BASE-T standard is a bus network.
A3:
Answer D is correct. Networks using the 10BASE-T standard did not
require coaxial cable. The bus structure however remained as a part of
the Hub. The correct way of describing an Ethernet using the 10BASET standard is a "star wired, bus network." Answer A is incorrect
because the 10BASE-T standard did not eliminate the use of a bus.
Answer B is incorrect because signaling remained in the radio spectrum
despite the use of cabling meeting the 10BASE-T standard. Answer C
is incorrect because severing a cable would only bring down the node
or station using the station.
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4.
Your uncle has a problem with his 10BASE-2 Ethernet and he has
asked for your help. He has several geographically dispersed offices in
a shared tenant office building. There are only 10 stations connected to
the network but 2 of the stations located in adjoining offices experience
erratic network behavior when communicating with each other. With the
exception of these 2 stations, the network performs well. You take a
look at each of the problem stations and find that each station has the
network cable attached to only one side of the "T" connector. The other
side of the "T" connector has a 3-inch black plug attached. Knowing
your uncle is short on cash, what would you recommend he buy to
remedy the problem with the 2 adjoining stations?
A. A patch cable to connect the stations in the adjoining offices and
complete the network path.
B. A 10BASE-2 repeater.
C. A non-filtering bridge.
D. A static or fixed configuration router.
A4:
Answer B is correct. Okay, this question really rambles but so will some
of the questions on the exam. The key to the question is seeing the
10BASE-2 cable attached to only one side of each station's "T"
connector. The plug attached to the other side of the "T" connector
should be a giveaway. Although these stations are in adjoining offices,
they are each at the end of the network cable. Even if you have never
seen one, you could probably guess that the black plug is actually a
terminating resistor, which confirms these stations as the ends of the
network. To communicate, these stations must send data across the
entire network. While we don't know the exact length of the cable, we
do know it streams off to connect the other geographically diverse
offices and then loops back almost to the starting point. That is probably
a "pretty good distance" (technical term). As only the end stations are
having problems, this is most likely an attenuation problem, which is a
Layer 1 (Physical) issue. The most efficient way to deal with Layer 1
attenuation is with a Layer 1 repeater. Okay, there are a lot of
assumptions here and not much in the way of cold hard facts, but that's
the way it is in the real world and, of course, it did make you think.
Answer A is incorrect because it would create a loop. Signals
introduced to a loop would continue around the loop until dissipated by
attenuation, which would effectively bring down the network. Answer C
could be correct because bridges provide a Layer 1 repeater function,
but they are really designed to provide Layer 2 capabilities, which would
not be used. Besides, bridges are more expensive than repeaters and
your uncle is strapped for cash. Answer D is incorrect because routers
are even more expensive than bridges and they operate at Layer 3. Of
course routers could be made to work, but you would need a pair of
them and you would end up with two separate networks. Definitely a
square peg in a round hole approach.
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5.
How does a transmitting station on an Ethernet recognize a collision
when it takes place?
A. A CRC is performed and if results do not match then a collision has
occurred.
B. The transmitting station cannot determine that a collision has taken
place while it is transmitting. It must wait until the receiving interface
recognizes the collision and sends an error report in the form of a jam
signal.
C. The interface does not monitor network errors. That is done at Layer
2 when the frame is checked for accuracy.
D. A voltage comparator on the transmitting interface senses an overvoltage condition on the line.
A5:
Answer D is correct. This is an area where there are a lot of old wives'
tales and any one of them will get you in trouble. Collision detection is a
Layer 1 issue for Ethernet dealing with voltage levels on the line. A
voltage comparator on the interface (it is really a $.22 chip) monitors the
voltage of the line even when the interface is transmitting. So long as
the voltage stays within a predetermined range, everything is okay.
However, when two or more signals are on the line at the same time,
the combined voltage exceeds this level. The comparator senses the
over voltage and it initiates the recovery process. Answer A is incorrect
because the Cyclical Redundancy Check is performed at Layer 2 and
indicates a fault with the data, which may not have been caused by a
collision. Answer B is incorrect because the voltage is monitored during
transmission. Answer C is incorrect because the question is asking
about a Layer 1 collision, not Layer 2 error detection.
6.
What is the Protocol Data Unit (PDU) used at Layer 4?
A. Frame
B. Segment
C. Packet
D. Data
A6:
Answer B is correct. Layer 4 is the Transport layer and Segment is the
name of its PDU. Answer A, Frame, is the PDU for Layer 2, Data Link.
Answer C, Packet, is the PDU for Layer 3, Network. Answer D, Data,
generally describes the PDUs for Layers 5 through 7.
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7.
A network administrator is charged with connecting LANs from the
Memphis production site to LANs at the Detroit headquarters. The
administrator leases a 56Kb line between the locations and terminates
the line with bridges to make the link as maintenance free and as
transparent as possible. The link meets all expectations but it is carrying
far more traffic than anticipated. In fact, the administrator is growing
increasingly concerned about degradation of response times. What
would you recommend?
A. Replace the bridges with cut through switches to increase
throughput.
B. Lease a second line to cover peak loads.
C. All of the above.
D. None of the above.
A7:
Answer D is correct. The administrator is linking networks at Layer 3
with a bridge, which is a Layer 2 device. Bridges would pass all of the
administrative traffic from both networks across the link, which could
easily fill whatever bandwidth was available. Although there are special
purpose bridges that could work in this situation, the real solution would
be to use routers. Routers would eliminate Layer 2 administrative traffic
from the link and free up bandwidth for data traffic. Answer A is
incorrect because a switch would also pass administrative traffic only
faster. Answer B is incorrect because it is addressing the symptom not
the problem. And now, will the administrator and all those choosing A,
B, or C please report to your new job in Marketing tomorrow morning.
8.
Which protocols are Layer 3 routable protocols? (Choose all that apply.)
A. Internet Protocol (IP)
B. Routing Information Protocol (RIP)
C. Internet Packet Exchange (IPX)
D. AppleTalk.
A8:
Answers A, C, and D are routable protocols that carry data between
networks. Answer B is a distance-vector routing protocol that is used by
routers to exchange routing table information and determine optimum
paths for packets.
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9.
People working at the end stations of a 10BASE-5 network are
constantly complaining that information they send each other is slow
and often has errors. Which devices may alleviate the problem?
(Choose all that apply.)
A. A bridge
B. A hub
C. A repeater
D. A static or fixed configuration router
A9:
Answers A and C are correct. The most likely cause of the problem is
attenuation of the signal as it crosses the cable. The end stations would
experience a majority of the problems because they have the most
cable between them. A repeater which rebuilds, retimes, and then
retransmits the signal would be the ideal short-term solution. Although a
bridge is designed to separate collision domains, its operation includes
rebuilding, retiming, and retransmitting frames just like a repeater. The
bridge provides more than is needed, but its repeater function would fix
the problem. Hubs are not used in a 10BASE-5 network so answer B is
wrong and answer D could go either way. If you could find a router with
both ports configured for 10BASE-5 networks, it could conceivably work
in this situation by rebuilding the signal as it was sent between
networks. The user, however, would have to be willing to accept the
higher costs of the router and the need to readdress many of the
stations and configure them all to use the router as a gateway. Certainly
not an elegant solution, and if this were the test I would not select it as a
viable solution.
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10.
A wiring technician was directed to extend a 10BASE-2 network cable
to provide service to a new suite of offices. The existing cable was too
short so the technician spliced a piece of cable that looked exactly like
the network cable but had different numbers printed on the jacket.
When the network was initialized the following morning, the entire
network experienced erratic operation. What would be the most likely
problem?
A. 10BASE-2 cable cannot be cut without introducing a high level of
attenuation. This attenuation can be great enough to stop all but the
strongest signals.
B. Joining even slightly dissimilar cables (the numbers didn't match)
would almost certainly create an impedance mismatch. The resulting
reflected signals would create erratic performance and could bring the
whole network down.
C. 10BASE-2 cable is extremely tolerant of mismatches so it is doubtful
the extension cable, even with a less than perfect splice, would cause
erratic operation. A more likely culprit would be a malfunctioning
vampire tap on the new cable.
D. None of the above.
A10:
Answer B is correct. We know that even a slight impedance mismatch
will reflect signals on any cable. Dissimilar cables, joined with a splice,
would be an invitation for disaster. So answer B would be the most
likely candidate. A splice would have to be unbelievably awful to create
an attenuation problem. Impedance mismatch yes, attenuation, not very
likely, which would make answer A incorrect. No cable is tolerant of
mismatched characteristics and besides that, vampire taps are not used
on 10BASE-2 cable so C is also incorrect. Answer B is related to the
material presented in the chapter and consistent with other examples.
So answer D can be ruled out.
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Chapter 4.
Wide Area Network Protocols
Terms you'll need to understand:










Frame relay
Data Link Connection Identifier (DLCI)
Local Management Interface (LMI)
Integrated Services Digital Network (ISDN)
Basic Rate Interface (BRI)
Primary Rate Interface (PRI)
Data terminal equipment (DTE)
Data communications equipment (DCE)
Point-to-Point Protocol (PPP)
High-Level Data Link Control (HDLC)
Techniques you'll need to master:




Switched services
Point-to-point and Point-to-multipoint connections
Peer-to-peer connections
Authentication
Wide area networking is a core business at Cisco. You will need to demonstrate
knowledge of major protocols and services inherent to wide area networking
when you sit for the CCNA test. This chapter will provide an overview of the
Point-to-Point Protocol, Frame Relay network operation, and Integrated
Services Digital Network components. While these are not the only protocols
and services included in wide area networking, they are representative, and
provide a foundation for presenting the protocols and services required by the
test.
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WAN Services.
Because WANs cover long distances, organizations typically subscribe to an
outside provider for WAN services. These services (usually telephone and data)
are routed from an interface at one end of the customer's network through the
provider's network to the other end of the customer's network.
It is the provider's responsibility to provide the customer with the parameters
necessary to connect to its network. The WAN provider's network appears as a
cloud to the customer, who simply makes a point-to-point connection to the
remote site.
The main interface between the customer and provider networks occurs between
the data terminal equipment (DTE) and the data communications equipment
(DCE).
TIP:
Be sure you are comfortable with the following terms as laid out in Figure 1:
 Customer Premise Equipment (CPE): Devices that are physically located
on the subscriber's premises. These devices are usually owned by the
customer or leased from the WAN provider.
 Demarcation (Demarc): The point where CPE ends and the local loop
begins, usually in the customer's main data closet.
 Local Loop (Last Mile): Cabling that extends from the demarc to the WAN
service provider's central office.
 Central Office (CO): The WAN service provider's switching facility, which
provides the nearest point of presence (POP) for the service. The service
provider's switching facility can also be called a POP.
 Data Terminal Equipment (DTE): Usually a router or bridge at the
customer's location that connects to the local loop through the DCE.
 Data Communications Equipment: A device at the end of the local loop
that attaches to the DTE. The DCE provides clocking and conversion of
data into a suitable format for transmission across the local loop.
Examples of Data Communications Equipment include modems, terminal
adapters (TA), network termination (NT1), and channel service unit/data
service unit (CSU/DSU).
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Figure 1. Connecting to the WAN service provider's network.
The customer's router usually serves as the DTE device and performs the
packet-switching function. Sometimes, DTE devices are bridges or terminals.
The DCE attaches to the DTE and provides clocking, converts the data into a
suitable format, and switches the data across the provider's network. DCE
devices include modems, a channel service unit/data service unit (CSU/DSU),
and a terminal adapter/network termination 1 (TA/NT1). The DTE/DCE interface
serves as the boundary where responsibility for the network traffic shifts from the
customer's network to the WAN provider's network. It can support several
common types of WAN service connections when the DTE is a Cisco router.
The first type involves switched services. Switches within the provider's network
transmit data from one customer DTE to that customer's other DTEs. Frame
Relay and ISDN are examples of packet-switched and circuit-switched services,
respectively.
The second type involves connecting remote devices to a central mainframe.
Synchronous Data Link Control (SDLC) is the protocol used in these types of
point-to-point or point-to-multipoint connections. SDLC is a bit-synchronous data
link protocol that supports legacy IBM networks.
A third type involves connecting peer devices. HDLC and PPP can be used to
encapsulate the data for transmission to peer DTE devices.
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Figure 2. Placement of DTE and DCE in a wide area network.
Figure 3. Common WAN services supported by Cisco equipment.
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TIP:
This chapter is full of acronyms and you will need to know them all for the test.
We will use them repeatedly to help you remember, but it would still be a good
idea to re-read this chapter prior to the test, just to be sure you feel comfortable
with the terminology.
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HDLC Overview.
High-Level Data Link Control (HDLC) is the default encapsulation used by Cisco
routers over synchronous serial links. HDLC is an ISO standard data link
protocol. It specifies a method to encapsulate data over synchronous serial links
using frame characters and checksums.
Cisco routers use a proprietary version of HDLC. Typically, HDLC is used on
leased lines between two Cisco devices. If you need to establish a link between a
Cisco router and a non-Cisco device, you must use PPP encapsulation instead of
HDLC.
TIP:
The ISO standard HDLC does not support multiple protocols on a single link.
However, Cisco's proprietary HDLC adds a field that allows it to support multiprotocol environments.
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PPP Overview.
Point-to-Point Protocol (PPP) encapsulates Network layer information for
transmission over point-to-point links. It was designed by developers on the
Internet and is described by a series of documents called Request for Comments
(RFCs)—namely, 1661, 1331, and 2153.
TIP:
PPP consists of two main components:
 Link Control Protocol (LCP)— Establishes, configures, and tests the
connection
 Network Control Program (NCP)— Configures many different Network
layer protocols
PPP Physical Layer
PPP can operate on a variety of DTE/DCE physical interfaces, including:
 Asynchronous serial
 Synchronous serial
 High-Speed Serial Interface (HSSI)
 ISDN
Other than what is required by a particular physical interface, PPP makes no
special transmission rate requirements.
PPP Connections
It is the responsibility of the Link Control Protocol (LCP) within PPP to establish,
configure, test, maintain, and terminate the point-to-point connection. Four
phases occur during the LCP process:
 Link establishment
 Link quality determination
 Network layer protocol negotiation
 Link termination
During link establishment, LCP opens the connection and negotiates
configuration parameters. Acknowledgment frames must be sent and received
before this phase can be considered completed successfully.
The link quality determination phase involves testing the connection to determine
whether the line quality is sufficient to support the Network layer protocols.
Although this phase seems very important, it is optional.
In the third phase, the appropriate Network layer protocols are configured.
Network control programs (NCPs) configure PPP to support different Network
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layer protocols, including Internet Protocol (IP), Internetwork Packet Exchange
(IPX), and AppleTalk. The PPP devices transmit NCP packets to select and
configure one or more Network layer protocols. After each selected Network
layer protocol has been configured, data can begin to be transmitted across the
link. If the LCP terminates a link, it notifies the NCP, which takes appropriate
action.
The link termination phase can be initiated by the LCP at any time. Link
termination can occur from events such as a user request, a loss of carrier, or the
expiration of a timeout parameter.
PPP Authentication
PPP authentication occurs during the link quality determination phase; therefore,
authentication is optional. The calling side of the link must transmit information to
ensure that the sender is authorized to establish the connection. This is
accomplished by a series of authentication messages being sent between the
routers. PPP supports two types of authentication: Password Authentication
Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP).
PAP
PAP uses a two-way handshake to allow remote hosts to identify themselves.
After the link has been established and the link establishment phase is complete,
PAP performs the following steps:
1. The remote host initiates the call, sends a username and password to the
local host, and continues to send the information until it is accepted or
rejected.
2. The local host receives the call and accepts or rejects the username and
password information. If the local host rejects the information, the connection
is terminated.
CHAP
CHAP uses a three-way handshake to force remote hosts to identify themselves
after the link establishment phase. CHAP performs the following steps after the
link establishment phase is complete:
1. The local router that received the call sends a challenge packet to the remote
host that initiated the call. The challenge packet consists of an ID, a random
number, and either the name of the local host performing the authentication
or a username on the remote host.
2. The remote host must respond with its encrypted unique ID, a one-way
encrypted password, the remote hostname or a username, and a random
number.
3. The local router performs its own calculation on the response values. It
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accepts or rejects the authentication request based on whether the value it
received from the remote host matches the value it calculated.
Like PAP, CHAP terminates the connection immediately if the local host rejects
the authentication request.
TIP:
During the PAP process, the username and password information is sent from
the remote host in clear text, so PAP is not a recommended protocol. It offers no
protection from a network analyzer capturing the information and using it.
Because CHAP uses secret, encrypted passwords and unique IDs, it is a much
stronger protocol than PAP. You can choose only one type of authentication, so
CHAP is definitely recommended; however, PAP is better than no authentication
at all.
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ISDN Overview.
ISDN refers to the call-processing system that enables voice, data, and video to
be transmitted over our existing telephone system. ISDN offers several
advantages over existing analog modem lines. For example, ISDN connection
speeds begin at 64Kbps, whereas typical modem speeds hover between
28.8Kbps and 56Kbps. The call setup time for an ISDN call is also much quicker.
ISDN can transmit data packets, voice, or video. ISDN is a viable solution for
remote connectivity (telecommuting) and access to the Internet. ISDN also
supports any of the Network layer protocols supported by the Cisco Internetwork
Operating System (IOS) and encapsulates other WAN services, such as PPP.
TIP:
ISDN can be used to:
 Add bandwidth for telecommuting
 Improve Internet response times
 Carry multiple Network layer protocols
 Encapsulate other WAN services
Basic Rate Interface and Primary Rate Interface
ISDN can be ordered as either BRI or PRI. An ISDN BRI service contains two
bearer channels (or B channels) of 64Kbps and one data channel (or D channel)
of 16Kbps. The B channel carries user data, and the D channel carries signaling
and control information. The maximum throughput for BRI is 128Kbps (two B
channels at 64Kbps). In North America and Japan, an ISDN PRI service uses a
T1 line that contains 23 B channels and one D channel, enabling a maximum
throughput of 1.544Mbps. In Europe, PRI service uses an E1 line that contains
30 B channels and 1 D channel, enabling a throughput of 2.048Mbps.
ISDN, like other communications services, requires Data Terminal Equipment
(DTE) and Data Communications Equipment (DCE). In most cases you will be
connecting a router to the ISDN BRI service and that router will have an ISDN
BRI interface. The interface can either be built in to the router's circuitry or take
the form of a module added to the router. Sometimes you will see the term "TE1"
(terminal equipment one) applied to routers without an interface and "TE2" used
for routers including the interface. In either case, that interface is the Data
Terminal Equipment (DTE) and in the world of ISDN BRI it is called a Terminal
Adapter (TA). The Data Communications Equipment that connects to the local
loop of the service provider is called a Network Termination One (NT1). The NT1
provides clocking and conversion of data into a suitable format for transmission
across the local loop. In North America, the service provider usually provides the
NT1 (but not always) and the user is responsible for providing power to the NT1.
Physically, the router's Terminal Adapter connects to the NT1 via a cable and the
NT1 connects to the local loop (see Figure 4).
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Figure 4. Interface devices used with ISDN.
ISDN PRI service has 23 bearer channels so it uses a larger ISDN PRI specific
DCE called a Data Service Unit and Channel Service Unit (DSU/CSU). The DSU
provides clocking and conversion of data while the CSU splits out the channels
for use by the Data Communications Equipment.
TIP:
In North America, ISDN BRIs can be provisioned without an NT1. In this case,
the customer is responsible for providing the NT1 and power for the NT1. Unlike
analog telephone lines, if you want a BRI to stay up during a power outage, you
must supply uninterrupted power to the NT1. This is not a problem for large
companies where wiring closets are supplied with a UPS or UPS service.
However, small firms and remote offices may not have a UPS, which can be a
problem. If IP telephony is used the problem becomes major.
DCE, DTE, CSU, and DSU are generic terms that apply to many types of
services. The TA is a type of DTE specific to ISDN, just like NT1 is a type of DCE
specific to ISDN BRI. These generic terms will come up over and over again so
be sure you understand the functions of each.
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DDR
Dial-on-demand routing (DDR) works with ISDN to establish and terminate
network connections, as traffic dictates. DDR configuration commands define
host and ISDN connection information. An access list and DDR dialer group
define what type of traffic should initiate an ISDN call. You can configure multiple
access lists to look for different types of "interesting" traffic—network traffic that,
when it arrives at the router, triggers the router to initiate the ISDN connection.
When the router notices interesting traffic, it refers to its ISDN information and
initiates the setup of the ISDN call through its BRI or PRI and NT1 device. It
should also be noted here that 56Kbps dial-up interfaces can also be used with
DDR. When the connection is established, normal routing occurs between the
two end devices. After interesting traffic stops being transmitted over the ISDN
connection, the connection idle timer begins. When the idle timer expires, the
connection is terminated.
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Frame Relay.
Frame Relay is a high-speed, packet-switching WAN protocol. Packet-switching
protocols enable devices to share the available network bandwidth. As its name
implies, Frame Relay operates at Layer 2 of the Open Systems Interconnection
(OSI) model and runs on nearly any type of serial interface. Frame Relay
encapsulates packets from the upper layers of the OSI model and switches them
through the provider's network.
Frame Relay services have been streamlined to gain more throughput. Services
such as flow control, robust congestion management, and error checking are left
to upper-layer protocols such as Transmission Control Protocol (TCP); however,
Frame Relay does include some error checking and congestion management.
Frame Relay uses cyclic redundancy checking (CRC) to perform error checking
quickly. CRC produces a frame check sequence (FCS), which is appended to
each frame that is transmitted. When a node receives the frame, it calculates a
new FCS (based on the data portion of the frame) and compares it with the one
contained in the frame. If the values are different, the frame is dropped.
Frame Relay manages congestion through the use of a discard eligibility bit. This
bit is set to a value of 1 if the frame has lower importance than other frames; the
DTE device is responsible for setting the bit and sets the bit to 1 for frames that
have lower importance than other frames. Switches within the WAN provider's
network may discard frames to manage congestion.
However, the switches only discard frames with the discard eligibility bit set to 1;
frames with bits set to 0 are still transmitted. This feature protects against critical
data being dropped during periods of network congestion.
Virtual Circuits
Communication in a Frame Relay network is connection oriented, and a defined
communication path must exist between each pair of DTE devices. Virtual
circuits provide the bidirectional communication within Frame Relay networks. In
essence, a virtual circuit is a logical connection established between two DTE
devices. Many virtual circuits can be multiplexed into one physical circuit, and a
single virtual circuit can cross multiple DCE devices within the Frame Relay
network.
Virtual circuits can be grouped into two categories: switched virtual circuits
(SVCs) and permanent virtual circuits (PVCs). SVCs are temporary connections
and can be used when only sporadic data communication is necessary between
DTE devices. SVCs require the connection to be set up and terminated for each
session. Conversely, PVCs are permanent connections. They support frequent
and consistent data communications across a Frame Relay network. When the
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PVC is established, DTE devices can begin transmitting data when they are
ready. PVCs are used more widely in Frame Relay networks than SVCs.
DLCI
A data link connection identifier (DLCI) serves as the addressing scheme within a
Frame Relay network. The service provider assigns a DLCI for each PVC, and
the DLCI is locally significant within the network. In other words, the DLCI must
be unique within the network like an Internet Protocol (IP) address. Two DTE
devices that have a PVC established between them may or may not use the
same DLCI value.
TIP:
Two methods can be used to map a DLCI to a Network layer address (such as
an IP address)—dynamically via inverse ARP or manually using the map
command. Both methods are discussed later. For now it is sufficient to know that
DLCIs can be configured manually or dynamically.
LMI
Local Management Interface (LMI) is a set of enhancements to the Frame Relay
protocol specifications. Developed in 1990 by four companies (nicknamed the
"Gang of Four"), LMI extensions offer several features for better management of
complex Frame Relay networks. These extensions include global addressing,
virtual circuit status messaging, and multicasting.
The "Gang of Four" includes Cisco Systems, StrataCom, Northern Telecom, and
Digital Equipment Corporation.
The LMI global addressing extension enables a DLCI to have global instead of
local significance. With LMI, DLCI values are unique within a Frame Relay
network, and standard address resolution protocols, such as Address Resolution
Protocol (ARP) and reverse ARP (or inverse ARP), as well as discovery
protocols can be used to identify nodes within the network. Virtual circuit status
messaging improves the communication and synchronization between DTE and
DCE devices. The status messages, which are similar to hello packets, report on
the status of PVCs. LMI multicasting enables multicast groups to be assigned.
Multicasting reduces overhead by allowing route updates and address resolution
messages to be sent to specific groups of DTE devices.
TIP:
Cisco supports the following Frame Relay LMI protocol variations:
 ANSI— American National Standards Institute
 q933a— International Telecommunication Union–Telecommunication
standardization sector
 Cisco— Gang of Four
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Exam Prep Questions
1.
Which protocol is responsible for establishing, configuring, testing,
maintaining, and terminating PPP connections?
A. BRI
B. PRI
C. LCP
D. NCP
A1:
The correct answer is C. LCP has the primary responsibility for a PPP
connection. Answers A and B are incorrect because BRI and PRI are
not components within PPP. Answer D is incorrect because NCP is
responsible for the configuration supporting Network layer protocols.
2.
Which of the following is an authentication type that would be
appropriate for an environment that requires strong encrypted
passwords?
A. PAP
B. CHAP
C. LCP
D. NCP
A2:
The correct answer is B. CHAP uses encrypted passwords, making it a
much stronger protocol than PAP. Answer A is incorrect because PAP
uses clear text to send passwords. Answers C and D are incorrect
because neither is an authentication type.
3.
Which of the following physical interfaces will PPP operate on?
A. Asynchronous serial
B. Synchronous serial
C. HSSI
D. ISDN
E. All of the above
A3:
The correct answer is E. PPP can operate on a variety of DTE/DCE
physical interfaces, including asynchronous serial, synchronous serial,
HSSI, and ISDN.
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4.
Which PPP authentication protocol uses a three-way handshake?
A. PAP
B. CHAP
C. LCP
D. NCP1
A4:
The correct answer is B. The CHAP three-way handshake includes the
local host requesting authentication, the remote host sending an
encrypted response, and the local host comparing the received
information and then accepting or rejecting the connection. PAP only
uses a two-way handshake. Therefore, answer A is incorrect. LCP and
NCP1 are not authentication protocols. Therefore, answers C and D are
incorrect.
5.
If your router does not have an ISDN BRI interface, which devices will
you need to connect to ISDN services? (Choose the two best answers.)
A. NT1
B. TA
C. TE1
D. TE2
A5:
The correct answers are A and B. You need a TA to convert the serial
signal from your router into a BRI signal, and you need an NT1 to
convert the BRI signal for use by the ISDN digital line. A TE1 is a device
that has a built-in BRI and already transmits BRI signals. Therefore,
answer C is incorrect. Answer D is incorrect because a device that does
not have a built-in BRI is considered a TE2.
6.
How can you use ISDN? (Choose all that apply.)
A. To improve Internet response times
B. To encapsulate other WAN services
C. To add bandwidth for telecommuting
D. To carry multiple Network-layer protocols
A6:
The correct answers are A, B, C, and D.
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7.
DCE devices provide which of the following functions?
A. Provides a clock to the DTE
B. Converts data into a suitable format
C. Switches data across the provider's network
D. All of the above
A7:
The correct answer is D. Answers A, B, and C are all functions of DCE
devices.
8.
Frame Relay operates at which layer of the OSI model?
A. Transport
B. Network
C. Data Link
D. Physical
A8:
The correct answer is C. Frame Relay operates at the Data Link layer.
Answers A and B are incorrect because Frame Relay does not include
any specifications for Layer 4 (Transport) or Layer 3 (Network).
Although Frame Relay can operate on several different physical media,
it does not include specifications for Layer 1 (Physical). Therefore,
answer D is incorrect.
9.
Which of the following devices can serve as a DTE device? (Choose
the two best answers.)
A. Router
B. Terminal
C. Modem
D. CSU
A9:
The correct answers are A and B. Routers and terminals can be
configured to act as DTE devices. Modems and CSUs cannot be
configured as DTE devices, but they can be configured as DCE
devices. Therefore, answers C and D are incorrect.
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10.
Which of the following are common WAN services supported by Cisco?
(Choose the five best answers.)
A. ISDN
B. Frame Relay
C. PPP
D. BGP
E. HDLC
F. SDLC
A10:
The correct answers are A, B, C, E, and F. ISDN, Frame Relay, PPP,
HDLC, and SDLC are all WAN services supported by Cisco equipment.
Although BGP is supported by Cisco equipment, it is an exterior routing
protocol. Therefore, answer D is incorrect.
11.
Which of the following can be used to establish bidirectional
communication between two DTE devices? (Choose the two best
answers.)
A. CVC
B. DVC
C. PVC
D. SVC
A11:
The correct answers are C and D. A permanent virtual circuit (PVC)
remains established between two DTE devices, even when data is not
being transmitted. A switched virtual circuit (SVC) is established only
when two DTE devices need to transmit data; it is disconnected when
the transmission is over. CVC and DVC are not related to virtual circuits
between DTE devices. Therefore, answers A and B are incorrect.
12.
Which of the following serves as the addressing scheme within a Frame
Relay network?
A. DLCI
B. LMI
C. NBMA
D. SVC
A12:
The correct answer is A. A DLCI number serves as the addressing
scheme and is assigned to each PVC. LMI provides several
enhancements to Frame Relay specifications. Therefore, answer B is
incorrect. Answer C is incorrect because NBMA describes how a router
must send broadcasts within a Frame Relay network. An SVC is
established to enable DTE to communicate. Therefore, answer D is
incorrect.
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13.
Cisco supports which of the following Frame Relay LMI protocol
variations? (Choose the three best answers.)
A. IETF
B. ANSI
C. Q933A
D. Cisco
A13:
The correct answers are B, C, and D. Cisco supports LMI extensions
from American National Standards Institute (ANSI), International
Telecommunication Union–Telecommunication standardization sector
(Q933A), and Cisco's "Gang of Four." Answer A is incorrect because
IETF is a type of frame encapsulation supported by Cisco that enables
Cisco devices to communicate with non-Cisco devices across a Frame
Relay network.
14.
Frame Relay uses what mechanism to perform error checking?
A. CRC
B. LMI
C. TA/NT1
D. Inverse ARP
A14:
The correct answer is A. Frame Relay uses CRC to derive the FCS,
which is a calculated value based on the data portion of each frame. If a
device calculates an FCS value that is different from the FCS value it
receives, the frame is dropped. LMI is communicated between DTE and
DCE devices and contains the status of the virtual circuit. Therefore,
answer B is incorrect. Answer C is incorrect because a TA/NT1 is a
DCE device and has nothing to do with error checking. Answer D is
incorrect because inverse ARP is the method by which DTE devices
discover Layer 3 protocol address information about each other.
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Chapter 5.
TCP/IP
Terms you'll need to understand:
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TCP
IP
FTP
UDP
ARP
RARP
DNS
Application layer
Transport layer
Internet layer
Network Access layer
Subnetting
Dotted decimal notation
Well-known port numbers
Techniques you'll need to master:
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Subnetting
Identifying the various layers of the TCP/IP model
Identifying the different classes of IPs
Performing a conversion from binary to dotted decimal notation
The Transmission Control Protocol/Internet Protocol (TCP/IP) is the foundation of
the Internet and the single most widely used protocol suite in the world today. A
detailed working knowledge of TCP/IP is required for the CCNA exam, so it is
very important you feel comfortable with everything presented in this chapter.
TCP/IP is not just a protocol, it is an entire suite of protocols which, together,
provide comprehensive rules and standards for communications (interdependent
protocols are called a protocol suite or protocol stack). Most presentations of
TCP/IP begin by showing how these protocols fit into the OSI model. The only
problem with this approach is that TCP/IP does not fit into the OSI model.
TCP/IP was developed under a four-layer model called the Department of
Defense model or DoD model. We will show you how these two models map to
each other as well as how the protocol suite fits into either model, because you
will need to know this for the test. However, if integrating TCP/IP into the OSI
model seems a bit awkward to you, it is only because it is.
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Background and History of TCP/IP.
In the late 1960s, Stanford University received funding from the Defense
Advanced Research Projects Agency (DARPA) to create and deliver a protocol
meeting the requirements of the four-layer Department of Defense model for data
communication. The specification further required full utilization of packetswitching technology, ability to communicate between dissimilar networks, and,
as this was the height of the cold war, complete survivability despite the end of
civilization.
The project was successful and the resulting protocols (collectively called
TCP/IP) became the cornerstone of the Defense Department's data
communications network called ARPAnet. ARPAnet expanded to include
universities participating in Defense Department research, and as more people
became accustomed to efficient global data communications, the pressure to
extend the capabilities also grew. Eventually, segments of the network branched
off into non-military areas. Two of the larger branches became The National
Science Foundation network (NSFnet) and a series of loosely defined networks
called the Internet.
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Four Layers of the DoD Model and the TCP/IP Protocol
Suite
Before we get into layers and protocols, you need to know about ports, a concept
that will come up repeatedly in TCP/IP. A port number identifies a sending or
destination application. Every application running on a host uses certain ports or
ranges of ports to communicate with applications running on other hosts. It is by
these port numbers that TCP or UDP determines which application to pass the
data to in the Application layer. The well-known ports have a value between 0
and 1,023. When an application on one device wants to communicate with an
application on another device, it must specify the address of the device (IP
address) and identify the application (port number).
PORT #
21
23
25
69
80
110
PROCESS
FTP
Telnet
SMTP
TFTP
HTTP
POP3
Be on the lookout for these port numbers and applications in the following
paragraphs. You will need to have them memorized for the exam!
Also, be sure to check out: http://www.iana.org/assignments/port-numbers for
information on other port numbers.
Let's start by looking at the specific functions and protocols of each of the four
layers. In Figure 1, we will look at how those layers and protocols map to the OSI
model later in the chapter.
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Figure 1. The four layers of the DoD model and associated protocols
from the TCP/IP suite.
Process/Application Layer.
The first layer of the model is the Process/Application layer. This layer is where
applications actually have to do something with the data once it is received. It is
important to note than any software application that uses the TCP/IP suite—such
as Internet Explorer, Outlook Express, or Adobe Acrobat Reader—needs to
communicate with the correct port for that application process on a receiving
computer. That is why these processes use well-known public port numbers.
Noteworthy to mention is that the sending port and receiving port do not have to
be the same, and generally are not the same. This layer also consists of a set of
services that provides access to all types of networks. Applications utilize the
services to communicate with other devices and remote applications. A large
number of TCP/IP services is provided at the Application layer, some of which
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were mentioned previously. In the following sections, you will see a list of several
Application layer protocols and their associated port numbers.
File Transfer Protocol (FTP)
FTP is used to copy a file from one host to another host, regardless of the
physical hardware or operating system (OS) of each device. FTP identifies a
client and server during the file transfer process. In addition, it provides a
guaranteed transfer by using the services of TCP. The services that TCP
provides are explained in more detail in the "Transport Layer" section of this
chapter. FTP uses port 20 or 21 to deliver files.
Trivial File Transfer Protocol (TFTP)
TFTP was built to be a small, robust FTP service. The original goal was to
develop a protocol that could fit into the limited read-only memory (ROM) space
of diskless machines. TFTP is a connectionless protocol that uses the services of
UDP for transport. TFTP is used to copy files from one host (server) to another
host (client). In many cases, TFTP is used to copy software to a device as it
boots up. A common use of a TFTP server is to upgrade the IOS of a Cisco
router, which you hopefully have already done or will be doing soon. TFTP uses
port 69.
Telnet
The Telnet service allows users to act as though their terminals are attached to
another device. This process is referred to as terminal emulation. Telnet is a very
useful protocol in internetworking because it allows network administrators to
view and configure remote devices in the network from one location. Telnet uses
the services of TCP to provide a connection-oriented session. Telnet uses port
23.
Simple Mail Transfer Protocol (SMTP)
SMTP is used to pass mail messages between devices. It uses TCP connections
to pass the email we've all grown to love between two mail servers. SMTP uses
port 25. More specifically, SMTP is what allows email to get from the mail client
to the mail server, whereas POP3 or Post Office Protocol is what gets mail from
the mail server to the mail client.
Simple Network Management Protocol (SNMP)
SNMP is used to obtain data on remote devices, such as a configurable switch.
Typically, a network-management station uses SNMP to poll the devices in a
network and to retrieve data regarding the devices' current and past conditions.
Each of the agents maintains a management information database (MIB) locally
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that constantly stores information about that device. The manager systematically
polls each of its agents, requesting information from their databases. It then
manipulates and organizes the data into a useful format for reporting or
displaying on the network-management monitor. SNMP has become the de facto
standard for device management and is widely used today.
Domain Name Service
DNS is a service that is used to translate hostnames or computer names into IP
addresses, such as www.awsb.ca. DNS is a hierarchical database of names and
their associated IP addresses. DNS allows people to enter a word-based address
for any device on the Internet. When this occurs, that person's device requests a
DNS lookup from a DNS server. The DNS server replies with the IP address
associated with that hostname. Can you imagine if this service never existed?
You would have to know the IP address of every Web site, effectively a
nightmare, so be happy. DNS uses port 53. DNS has some security issues as
well because it uses port 53 for both UDP and TCP traffic.
Transport Layer
The next layer for us to look into is the Transport layer. The Transport layer
passes data between the Application layer and the Internet layer. It consists of
two protocols, Transmission Control Protocol (TCP) and User Datagram Protocol
(UDP). This layer provides an end-to-end connection between two devices,
otherwise referred to as host-to-host communications, during communication by
performing sequencing, acknowledgments, checksums, and flow control. The
Transport layer allows the Application layer to ignore the complexities of the
network and focus on its primary job. This layer is also responsible for sending
data that it receives from the Network layer to the appropriate application.
TCP
TCP provides a connection-oriented, reliable service to the applications that use
its services. TCP was designed to add some reliability into the world of IP
networking. A description of the main functions of TCP follows:
 Initiates connection with three-way handshake— TCP uses the concept of
the three-way handshake to initiate a connection between two devices. A
TCP connection begins with device A sending a request to synchronize
sequence numbers and initiate a connection (a SYN message). Device B
receives the message and responds with a SYN message with the
sequence number increased by one. Device A responds by sending an
acknowledgement message (an ACK) to device B, indicating that the
device received the sequence number it expected.
 Performs error and duplication checking— TCP uses a checksum to
identify packets that have changed during transport. If a device receives a
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packet with a bad checksum, it drops the packet and does not send an
acknowledgment for it. Therefore, the sending device resends the packet
(hopefully, it will not change during transport this time). In addition, any
time TCP receives a duplicate packet, it drops the duplicate.
Performs acknowledgment windowing to increase efficiency of bandwidth
use— Any time a TCP device sends data to another device, it must wait
for the acknowledgment that this data was received. To increase the
efficiency of bandwidth utilization, TCP can change the window size. If the
window size is increased to 2, the sending device requires only one
acknowledgment for every two packets sent. TCP sets the window size
dynamically during a connection, allowing either device involved in the
communication to slow down the sending data rate based on the other
device's capacity. This process is often referred to as sliding windows
because of TCP's ability to change the window size dynamically.
Segments Application layer data stream— TCP accepts data from
applications and segments it into a desirable size for transmission
between itself and the remote device. The segment size is determined
while TCP is negotiating the connection between the two devices. Either
device can dictate the segment size; however, the receiving station is
given priority.
Provides acknowledgment timers— TCP maintains timers to identify when
packets have taken too long to get to their destination. When an
acknowledgment is not received for an IP packet before the expiration of
the timer, TCP resends the packet to the destination.
Enables sequence number checking— TCP/IP uses sequence number
checking (TCP) sequence numbers to ensure that all packets sent by an
application on one device are read in the correct order by an application
on another device. The packets might not be received at the Transport
layer in the correct order, but TCP sequences them in their original order
before passing them to the Application layer.
Provides buffer management— Any time two devices are communicating,
the possibility exists that one device can send data faster than the other
can accept it. Initially, the receiving device puts the extra packets into a
buffer and reads them when it gets a chance. When this data overflow
persists, however, the buffer is eventually filled and packets begin to drop.
TCP performs some preventive maintenance called flow control to avoid
this scenario.
Do not get too bogged down and overwhelmed by the amount of information on
TCP and its functions. Merely understand what it does and that the main point to
know is that TCP is connection-oriented and a reliable service.
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UDP
UDP is a connectionless protocol that will run on top of an IP network. One of the
disadvantages of UDP is that it provides very few error recovery services.
However, one's disadvantage is another's advantage. Because there is no error
checking, UDP is considerably faster than TCP. The primary purpose of UDP is
to broadcast messages over a network. UDP simply receives data from the
Application layer, applies the proper header, and sends the datagram on its
merry way. This is why UDP is referred to as a best-effort protocol.
Internet Layer
The Internet layer is responsible for path determination and packet switching.
The Internet layer utilizes a logical addressing scheme to make intelligent
decisions regarding path determination and packet switching. The Internet layer
performs the actual relay of packets from an originating network to a destination
network in an efficient manner. Every packet is viewed by IP, which determines
its destination by using a routing table. The routing table helps establish the best
path for the packet to be sent.
IP
Internet Protocol (IP) is the transport for TCP, UDP, and Internet Control
Message Protocol (ICMP) data. IP provides an unreliable service and is
effectively a connectionless protocol. I know this is hard to imagine, but
remember that the transport layer above it does all the error checking, so this
layer does not have to worry about it. It lets the upper-layer protocols, such as
TCP, or application-specific devices worry about reliability. In addition, IP
performs as a connectionless service because it handles each datagram as an
independent entity. IP performs packet switching and path determination by
maintaining tables that indicate where to send a packet based on its IP address.
Address Resolution Protocol (ARP)
ARP is a TCP/IP protocol that is used to convert an existing IP address into a
physical address. Consider a computer that wants to know the address of
another computer. The computer sends out (broadcasts) an ARP request to the
network. The receiving computer that owns the physical address being sought
replies to the original computer that was looking for its address. Sound rather
simple? It is.
Reverse Address Resolution Protocol (RARP)
RARP provides the exact opposite type of mapping from ARP—that is, RARP
maps a known physical address to a logical address. A diskless machine that
does not have a configured IP address when started typically uses RARP. These
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devices send a broadcast requesting an IP address. In such a scenario, a device
on the same local area network (LAN) is designed to respond to this broadcast
request and supply the IP address for that physical address.
Internet Control Message Protocol (ICMP)
ICMP communicates error messages and control messages between devices.
The ICMP protocol allows devices to check the status of other devices, query the
current time, and perform other functions. The most popular use of ICMP is the
use of the PING command. The PING command uses ICMP to test an Internet
connection. The Ping command is an excellent command used for
troubleshooting, but you probably already know that by now, don't you? The most
common ICMP messages are as follows:
 Destination unreachable— Indicates that a certain device cannot be
contacted
 Time exceeded— Indicates that a certain device could not be reached
within a specified time limit
 Echo— Requests an echo reply to determine device reachability
 Echo reply— Replies to an echo request indicating that a host is
reachable
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Network Interface Layer
The Network Interface Layer does just as its name implies: It works at the
hardware level to define the physical transmission of signals along the network. It
effectively encapsulates information into frames (remember encapsulation?) that
can be transmitted across the network. This layer provides access to the LAN.
The physical addressing and network-specific protocols exist at this layer. Token
Ring, Ethernet, and Fiber Distributed Data Interface (FDDI) are some examples
of Network Interface layer protocols, as can be seen in Figure 2.
Figure 2. This graphic shows how the OSI model (left) maps to the DoD model
(right). You should be familiar with how these two models relate for the test.
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IP Addressing.
Every computer that communicates on the Internet is assigned a unique IP
address that identifies the device and distinguishes it from other computers on
the Internet. This section looks at the various classes of IP addressing and pays
great attention to examples of each, as you will be required to know the various
classes by heart for a Cisco examination.
Binary Notation
Let's start right off by making an unbelievable claim: IP addressing is a simple,
straightforward, easy-to-remember method for uniquely identifying a device to the
rest of an IP network. Nobody seems to have a problem with the part about
uniquely identifying devices, but as far as being "simple and easy to
remember"…no way! Actually, IP addressing is only complex because it is
invariably presented as a mix of base 2 math, base 10 math, a little hexadecimal
for interest, and a seemingly endless number of arbitrary rules. Instead of
adopting this approach, let's look at IP addressing as it was developed.
The people who developed IP were real geeks. They coded in base 2, were
comfortable using base 2, and, of course, the native language of computers was
base 2 machine language. Why would they develop IP in anything other than
base 2? 32 digits could be grouped into four octets, which easily fit in computer
registers and provided a reasonable range of addresses. However, 32 digits only
provided a reasonable range if organized in a hierarchical structure, and this is
where it got interesting. If all 32 digits were used in a linear address, there could
be 1 network with a little more than four trillion stations, or slightly over four trillion
networks with 1 station each.
Either scenario made a good argument for dividing the digits, with some
identifying the network and some identifying the station. The big question would
be where to make the division. If the 32 digits were allocated evenly (16 to
network address and 16 to station address), there could be up to 65,535
networks with each having up to 65,535 stations each. Sounds reasonable, but
wouldn't it be neat if the division could be variable depending on need?
Geeks like neat and these geeks worked with the Defense Department so a little
cryptography produced the ideal solution; the address would become a code
within a code. If the first bit (the leftmost or most significant bit) of the address
was zero, then the first octet would be the network address and the remaining
three octets would form the station or host address. This would yield up to 126
networks (2 are reserved for testing and broadcast) and more than 65 million
hosts on each network. If the first 2 bits were "10", then the first two octets would
be the network address and the last two octets would be the host address.
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This provided more than 16 thousand networks and more than 65,000 hosts on
each network. If the first three digits were "110" then the first three octets would
be network addresses and the last octet would be host addresses. More than 2
million network addresses, with 256 host addresses on each network, would be
provided with this structure. Of course, special use addresses are required for
any network, so addresses where the first four digits were "1110" were reserved
for multicast/broadcast, and addresses starting with "11110" were reserved for
experimentation.
This in a nutshell is IP addressing: simple, straightforward, and easy to
remember (so long as you work with it in binary). Later the four address
structures would be labeled A, B, C, and D, and binary would be converted to
base 10 and formatted as dotted decimal notation. Unfortunately, the relations
that are so easy to see in binary are unrecognizable in dotted decimal notation.
TIP:
You should be able to quickly perform conversions between decimal and binary
for the exam. If you are the least bit unsure, spend a few hours practicing before
the exam (no calculators are allowed). If you get stuck while taking the exam,
work the problem out in binary and then convert to decimal.
Dotted Decimal Notation
IP addresses are typically shown in dotted decimal notation, which was
developed so that people could easily read and write IP addresses. You already
know that an IP address in its native form is binary. You also know that the
address is composed of 32 bits that have been divided into 8-bit groups, referred
to as octets or bytes. An IP address in dotted decimal notation specifies the
decimal equivalents of each of the four octets, separated by dots. An example of
a dotted decimal IP address is 209.128.50.98.
Each octet can have a decimal value between 0 and 255. Why would there be
such a limitation, you ask? The total number of possible values for a binary
8
8
number with 8 bits can be written mathematically as 2 . Although 2 has a total
value of 256, IP addresses begin with the number 0 instead of 1; therefore, the
decimal range starts at 0 and ends with 255, for a total of 256 possible values.
IP Classes
The number of bits assigned to the network ID and the host ID depends on the
number of hosts required on a given network and the number of networks
required in an environment. Before the idea of classful addressing was in place, it
was the network administrator's responsibility to determine which bits in the 32bit address to assign to the network ID and which bits to assign to the host ID. If
the number of hosts required on a given network was enormous, the network
administrator assigned a large portion of the 32 bits available to host IDs and
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used a small portion for network IDs. If a large number of networks were required
with only a few hosts per network, the network administrator used a small portion
of the bits for host IDs and a large number for network IDs.
This method of allocating address space was inefficient, often giving small
organizations the right to a large number of IP address spaces. Therefore, IP
address space was divided into three classes in the attempt to meet the needs of
large and small organizations. (Actually, the IP address was divided into five
classes; however, we will focus on the three more commonly used classes.) With
the class system, it is possible to assign a corporation address space based on
the number of hosts and networks it requires. This system is referred to as
32
classful addressing. Classful addressing divides the 4,294,967,296 (2 )
possible IP addresses into five different classes.
The first 3 bits of the address indicate a class A, B, or C IP address. After a
while, you will only need to look at the first octet of an IP address in decimal
format to determine its class. The class of an IP address governs the number of
bits that can be used for network IDs and the number of bits that can be used for
host IDs. For example, an organization that is allocated a class B address must
use 16 bits to identify its network ID and 16 bits to identify its host ID. It is
important to note that this strict rule can be avoided, and most often is, through a
process known as subnetting.
Class A
Class A addresses are typically assigned to very large organizations,
universities, and the military. It is extremely difficult—if not impossible—to get a
class A address today. These addresses are identified in binary by the first bit
having a value of 0 or in decimal by having a value between 1 and 126. Class A
addresses use the first 8 bits to specify the network ID and the last 24 bits to
designate the host ID.
A maximum of 126 class A network IDs are available. This value is arrived at by
taking the number of bits used for the network ID to the power of 2. In this case,
7
2 equals a total of 128 (only 7 bits are available because the first bit must be 0).
However, the network ID 0.0.0.0 is reserved for the default route, and the
network ID 127.0.0.0 is reserved for the loopback function. Therefore, the range
of possible class A network IDs in decimal is 1 to 126.
Although you may never need to know the exact number, each class A network
ID can support a total of 16,777,214 (2 24–2) host IDs. The purpose of subtracting
2 from the possible number of hosts is to remove two special host IDs. Any time
every bit in the host ID portion of an IP address has a value of 1, it is considered
a broadcast IP address, meaning that all hosts in the network should read a
message sent to this address, like an ARP request. Obviously, no device should
have an address that is used for broadcasting information. The second
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consideration is when every bit in the host ID's binary value is 0. This value is
used to denote a network ID number.
Class B
Class B addresses are typically assigned to medium and large organizations.
These addresses are identified in binary by the first 2 bits having a value of 10, or
in decimal by having a value between 128 and 191. Class B addresses use the
first 16 bits to specify the network ID and the last 16 bits to designate the host
IDs. Because the first 2 bits of all class B addresses are always 10, however,
only 14 bits are available to be used for network IDs. This allows a total of 16,384
14
(2 ) class B network addresses. Each network ID supports a total of 65,534
(216–2) host IDs.
Class C
Class C addresses are typically assigned to small and medium organizations.
These addresses are identified in binary by the first 3 bits having a value of 110,
or in decimal by having a value between 192 and 223. Class C addresses use
the first 24 bits to specify the network ID and the last 8 bits to designate the host
IDs. Because the first 3 bits of a class C address are 110, however, only 21 bits
are available to be used for network IDs. This allows a total of 2,097,152 (2 21)
8
class C network addresses. Each network ID supports a total of 254 (2 –2) host
IDs.
TIP:
You will see several questions relating to classful addresses. If you memorize the
dotted decimal ranges for A, B, and C class addresses, you will be able to quickly
answer these questions. You can always work them out in binary, but the time
taken to do that cannot be used on other questions.
Other Classes
Two other classes of addresses are also available but generally not used in the
public address space; these have been reserved for specific functions. Class D
addresses are identified in binary by the first 4 bits having a value of 1110, or in
decimal by having a value between 224 and 239. Class D addresses have been
reserved to support IP multicasting, which is the process of using one address
to send a message to a group of people. The main benefit of sending a chunk of
data headed for multiple destinations is that it has to be sent between the transit
routers only once, and therefore a ton of bandwidth is conserved. Class E
addresses are identified in binary by the first 5 bits having a value of 11110, or in
decimal by having a value between 240 and 247. Class E addresses have been
reserved for experimental or research use.
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Subnetting.
One of the major goals of classful addressing is the ability to assign one and only
one address to an organization. However, few organizations can function with
just one network address. Subnetting provides a solution for this problem.
Default Mask
A default mask is a 32-bit number divided into four octets, just like an IP address.
A default mask indicates the number of bits used to identify the network ID, and
it's implied with all class A, B, and C addresses. Class A addresses imply an 8-bit
default mask because the first 8 bits in these addresses designate the network
ID. Therefore, the default mask (the number of bits that indicate the network ID)
can be represented in decimal format as 255.0.0.0.
Why do we need a default mask if we can already determine this by the class of
the IP address? As mentioned previously, organizations often have the need to
increase the number of networks in their intranet. However, when an organization
has only one block of IP addresses it can advertise to the Internet but wishes to
have many subnetworks in its environment, the organization can indicate that it
has used some of the host ID bits as network ID bits by providing a subnet mask.
Subnet Mask
A subnet mask is an extension to the default mask. It indicates the number of bits
in addition to the default mask that should be used to identify network IDs. What
does this do for an organization? It increases the number of networks an
organization can create from one class A, B, or C network ID.
For example, if an organization has a registered class C address and needs to
create two networks, it must somehow get more network IDs. The organization
can accomplish this by using some of the bits designated as host IDs as network
IDs. However, the organization must indicate that this class C address is no
longer using the default 24 bits as a network ID. The organization can indicate
this by applying a subnet mask to represent the additional bits that are to be used
as network IDs versus host IDs. The subnet mask can be represented in various
ways; in this chapter, we will refer to the subnet mask as the default mask plus
any additional bits used for network IDs.
Logical ANDing
How should the subnet mask be used to determine the network ID for an IP
address? To determine the network ID and the host ID for an IP address, it is
necessary to perform a process known as logical ANDing. When information is
sent to a router and is destined for a remote location, the router cares only about
which network to send the information to.
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The router knows the subnet mask and the destination IP, so the ANDing
process is used with these two addresses to determine the network portion of an
IP address and then a routing table is used to determine the remote network to
send the information to. This indicates which bits to use as network bits and
which bits to use as host bits when the IP address is deciphered. When the
subnet mask is applied to an IP address, each bit starting from the most
significant bit to the least significant bit is compared between the IP address and
the subnet mask. For example, the first bit of the first octet of the IP address is
compared with the first bit of the first octet of the subnet mask. The resulting
value from this bit-by-bit comparison is the network ID. The rule set to apply is
listed as follows:
 If the subnet mask and the IP address both have values of 1, the resulting
network ID bit is 1.
 If the subnet mask has a value of 1 and the IP address has a value of 0,
the resulting network ID bit is 0.
 If the subnet mask has a value of 0, the resulting network ID bit is 0.
So far, you have learned that IP addresses are divided into classes to allocate
the IP address space to varying sizes of organizations efficiently. Efficient
allocation of address space also minimizes the number of entries that need to be
maintained in the routing tables of Internet routers. Because organizations
required more networks than the InterNIC believed reasonable to assign due to
wasted IP address space, a subnet mask was created, giving organizations a
tool for increasing the number of networks they had by borrowing bits from the
host IDs of their assigned IP address space. A subnet mask uses the logical
AND process to distinguish between the network ID and the host ID of an IP
address.
Next, we'll discuss some of the items to consider when determining the number
of bits to use for the subnet mask. A bad decision on a subnet mask can place
constraints on an organization's future addressing choices.
Subnetting Consideration
Remember that the purpose of the subnet mask is to give an organization the
flexibility to increase the number of networks in its environment. So, you might
think that an organization should give itself the maximum number of networks
possible with its assigned IP address space. Any time a bit is added to the
network ID, however, a bit is removed from the host ID. Therefore, if the number
of networks is increased, the number of host IDs available per network is
decreased.
Organizations need to determine the happy medium between sufficient host IDs
and network IDs for their specific needs. The cost of changing the subnet mask
on thousands of computers because of a scaling issue is not a welcome thought
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for network administrators. Here are some of the questions that must be asked
before a subnet addressing scheme is developed:
 What is the total number of network IDs the organization needs today?
 What is the total number of host IDs the largest network requires today?
 What is the total number of network IDs the organization will need in the
future?
 What is the total number of host IDs the largest network will require in the
future?
The answers to these questions will determine how an organization subnets its
assigned IP address space. The purpose of asking about current and future
requirements is to get an understanding of what is absolutely needed today and
what should be planned for the future. To illustrate the process of classful IP
addressing, subnetting, and logical ANDing as well as IP addressing
considerations, examples using class A and C addresses are provided in the
following sections.
The next few sections will give some real good examples of subnetting. If you are
comfortable with this concept, congratulations, you may proceed to another
section. If you are not comfortable, please read on. Beware, you will be tested
extensively on this section for the CCNA exam.
Class A Network Example
This example uses a fictitious company named AWSB to illustrate the process of
determining the proper subnetting for an organization. AWSB has been allocated
the class A IP address 114.0.0.0 by the InterNIC. AWSB must determine the
proper way to use this IP address space to support its current and future needs.
To determine these needs, we must answer the four questions suggested
previously. These questions are repeated here, along with AWSB's responses to
them:
 What is the total number of network IDs AWSB needs today? Answer:
5,000.
 What is the total number of network IDs AWSB will need in the future?
Answer: 9,000.
 What is the total number of host IDs AWSB requires on its largest network
today? Answer: 1,000.
 What is the total number of host IDs AWSB will require on its largest
network in the future? Answer: 2,000.
AWSB has been assigned only one network ID; however, it needs lots more to
support its current and future requirements. AWSB plans to use subnetting to
create more network IDs. As mentioned previously, by default, 24 bits are
allocated for host IDs with a class A IP address space. We know that AWSB
requires 5,000 networks today and 9,000 in the future. Therefore, to create
enough network IDs, we have to take bits from the host IDs and use them for
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network IDs. How many bits have to be taken from the host ID bits to provide
5,000 network IDs?
AWSB requires a total of 13 bits to provide 5,000 network IDs. The number of
13
bits required can be determined by taking 2 (for a total of 8,192 possible
networks). A subnet mask of 255.255.248.0 is used to represent the 13 bits of
subnetting. However, 13 bits provide only 8,192 total possible networks, which is
not enough to support AWSB's expected growth. A total of 14 bits is required to
ensure that 9,000+ networks can be supported in the future. If AWSB uses 14
bits as the subnet mask (a subnet mask of 255.255.252.0), it has a total of
16,384 (214) possible network IDs. AWSB would prefer to use 14 bits of the host
ID to subnet the current 114.0.0.0 class A address; however, taking 13 bits from
the host ID would provide a sufficient number of network IDs (subnets) to provide
for today's needs.
AWSB must determine whether enough bits still remain to provide an adequate
number of host IDs. AWSB requires 1,000 host IDs per network today and
expects to need 2,000 host IDs per network in the future. How many bits are
required to provide 1,000 host IDs? How many bits are required to provide 2,000
host IDs? How many bits are still available to be used as host IDs?
The number of bits required for 1,000 host IDs is 10, which provides a total
10
combination of 1,022 (2 –2). Remember that we subtract 2 to represent the
broadcast (all 1s) and the zero (all 0s) value in each network. However, AWSB
requires 11 bits to provide sufficient host IDs to support its future requirement of
2,000 hosts.
AWSB has only 24 bits of host IDs in its class A 114.0.0.0 IP address to use for
both hosts and networks. To get enough host IDs for 2,000 users per network
and 9,000+ network IDs, however, it would take 14 network ID bits and 11 host
ID bits, for a total of 25 bits. AWSB is short 1 bit, so it has to decide whether to
limit the number of hosts or networks to have in the future. In this case, AWSB
would probably opt to use only 13 bits (8,192 networks) for network IDs and 11
bits for host IDs (2,046 host IDs per network). The decision can become more
difficult, however, when an organization doesn't have the luxury of owning an
entire class A IP address.
Class C Network Example
In this example, we will define the actual subnets and host IDs. If an organization
named AWSB has been assigned the IP address space 210.14.12.0, it has been
assigned a class C address with a default mask of 255.255.255.0. This
organization requires five networks today and expects to need eight in the future.
In addition, AWSB expects the largest number of hosts on a given network now
and in the future to be 30 users.
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AWSB requires more networks and must subnet the 8 bits allocated to host IDs
to provide these networks. To do so, AWSB must subnet 3 bits to provide eight
more networks (23 ). The subnet mask of this IP address is now 255.255.255.224.
The value of the last octet has changed to represent the 3 bits (128 + 64 + 32 =
224) that are now used to identify networks instead of hosts. However, AWSB
must make sure that it will have enough host IDs left to identify all 30 devices on
its largest network. AWSB has 5 bits remaining for host IDs, giving it a total of 30
(25 –2) host IDs per network.
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Summary of Subnetting.
You have seen that flexibility has been built into IP addressing via a process
known as subnetting, which allows organizations to divide up classful network
IDs into a number of other networks. Any device can determine how an IP
address is divided by looking at the IP address's subnet mask. This mask
indicates which bits have been used for subnetting and which bits are still being
used to identify hosts. Of course, each class of IP address has a default mask.
Furthermore, we identified some important questions to consider when setting up
an addressing scheme. Specifically, you need to know the number of hosts and
networks an organization requires in the present and the future.
The ability to do subnet masks on the fly for the CCNA exam is crucial. The good
news is that this ability is also crucial to being proficient at networking in general.
Therefore, feel good about spending a significant amount of time practicing the
art of subnetting.
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Exam Prep Questions
1.
The following IP address is listed in dotted decimal format. What is the
corresponding binary value of this IP address?
112.14.12.8
A. 01100000.00110000.01101111.10110111
B. 0.11.0.11
C. 01110000.00001110.00001100.00001000
D. 01110000.00001110.11000000.00110011
A1:
The correct answer is C. The conversion of these binary bits yields a
decimal value of 112.14.12.8. Answer A can be identified quickly as
incorrect by noting that the fourth octet begins with 1, but its value is not
greater than 128. Answer B can be eliminated immediately because it is
not in the format of a binary IP address. Answer D can be judged to be
incorrect by determining the decimal value of either the third or fourth
octet. It is important to note that it is not necessary to convert each one
of the possible answers into decimal format. It is much quicker to
eliminate the obviously wrong answers (such as B) and then isolate
reasons to remove other answers before converting any values.
2.
Which of the following statements is not true concerning the deciphering
of a subnet ID from an IP address and subnet mask using the ANDing
process?
A. If the subnet mask and the IP address both have values of 1, the
resulting network ID bit is 1.
B. If the subnet mask has a value of 1 and the IP address has a value
of 1, the resulting network ID bit is 0.
C. If the subnet mask has a value of 1 and the IP address has a value
of 0, the resulting network ID bit is 0.
D. If the subnet mask has a value of 0, the resulting network ID bit is 0.
A2:
The correct answer is B. It specifies that a network ID bit of 0 is the
result when comparing a subnet mask bit with a value of 1 and an IP
address with a value of 1. This is not one of the rules used to decipher
network IDs. Therefore, answer B is the correct answer. Answers A, C,
and F are the three rules presented in this chapter for deciphering
network IDs from an IP address with a subnet mask. Therefore, these
answers are incorrect.
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3.
Which of the following tools can be utilized to test IP connectivity
between two devices? (Choose the three best answers.)
A. Ping
B. Telnet
C. Traceroute
D. show ip interface
E. show ip protocol
A3:
The correct answers are A, B, and C. Ping, Telnet, and Traceroute are
all tools mentioned in this chapter for testing IP connectivity between
two devices. Answers D and E are incorrect because show ip interface
and show ip protocol are used to monitor IP addresses and the
functioning of IP within a local router.
4.
Which of the following tools will identify the address of intermediate
hops between two destinations?
A. Traceroute
B. Telnet
C. Ping
D. Rlogin
E. TCP
A4:
The correct answer is A. The traceroute command can be used to
identify the address of every intermediate hop between two locations.
Answer B is incorrect because the telnet command is used to obtain
remote control of a destination device. Answer C is incorrect because
the ping command only tells users whether they have IP connectivity.
Answer D is incorrect because rlogin is a command used for remote
access on Unix machines. Finally, answer E is incorrect because TCP
is a Layer 4 protocol, and it is not used for testing IP connectivity.
5.
Which of the following is the default mask of a class A IP address?
A. 255.0.0.255
B. 255.255.0.0
C. 255.0.0.0
D. 255.255.255.0
A5:
The correct answer is C. Class A addresses have a default mask of 8
bits, or 255.0.0.0. Answer A is incorrect because all default masks are
made up of contiguous bits. Answer B is incorrect because 255.255.0.0
is the default mask of a class B IP address, not a class A IP address.
Answer D is incorrect because 255.255.255.0 is the default mask of a
class C IP address, not a class A IP address.
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6.
Which of the following terms does not identify a layer of the TCP/IP
model?
A. Application
B. Transport
C. Presentation
D. Internet
E. Network access
A6:
The correct answer is C. Only the OSI model uses the Presentation
layer; therefore, this term does not identify a layer of the TCP/IP model.
Answers A, B, D, and E all identify separate layers of the TCP/IP model.
7.
Which of the following services exist at the Application layer of the
TCP/IP model? (Choose the best answers.)
A. SMTP
B. FTP
C. ICMP
D. ARP
E. TFTP
A7:
The correct answers are A, B, and E. SMTP, FTP, and TFTP all exist at
the Application layer of the TCP/IP model. Answer C is incorrect
because ICMP exists at the Internet layer of the TCP/IP model. Answer
D is incorrect because ARP exists at the Internet layer of the TCP/IP
model.
8.
If you wanted to locate the hardware address of a local device, which
protocol would you use?
A. ARP
B. RARP
C. ICMP
D. PING
A8:
The correct answer is A. If you know the IP address and you are trying
to find the hardware (MAC) address, ARP is the choice. Answers C and
D are incorrect because a ping command is used to verify network
connectivity and sends ICMP packets to determine this. RARP, answer
B, is incorrect because it will find the IP address, given the hardware
address.
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9.
Which of the following services is used to translate hostnames into IP
addresses?
A. SNMP
B. SMTP
C. IP
D. UDP
E. DNS
A9:
The correct answer is E. DNS is used to translate word-based
addresses into IP addresses, or vice versa. SNMP and SMTP are
TCP/IP Application layer services, but they do not perform address
translation. SNMP is used to monitor remote devices, and SMTP is
used to send email between devices. IP is not a service but rather a
protocol used for logical addressing and routing. Therefore, answers A,
B, and C are incorrect. Finally, UDP is a Transport layer protocol used
for packet sequencing, which makes answer D incorrect.
10.
Which of the following functions is not performed by TCP?
A. Flow control
B. Sequencing
C. Error checking
D. Subnetting
A10:
The correct answer is D. Subnetting is not a function performed by
TCP; it is a process used to create more networks out of classful IP
addresses. Answer A is incorrect because TCP does indeed provide
flow control in the form of sliding windows and buffer management.
Answer B is incorrect because TCP provides sequencing to ensure that
datagrams are read in the correct order on the receiving side. Finally,
answer C is incorrect because TCP provides error checking by applying
a checksum to the TCP header and encapsulated data.
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Chapter 6.
Cisco Layer 2 Switching
Terms you'll need to understand:
Spanning Tree Protocol
Store-and-forward switching
Fragment-free switching
Cut-through switching
Virtual Local Area Network (VLAN)
VLAN ID
VLAN Trunking Protocol (VTP)
Techniques you'll need to master:
Filtering and forwarding frames
Preventing loops
Discovering MAC addresses
Frame tagging
Inter-switch link
We will present switching technology, as Cisco views it. Many of the features and
protocols we will be talking about are proprietary to Cisco or pioneered by Cisco.
Therefore, even if you feel you know the technology, read this chapter carefully.
Switching is a major product technology for Cisco and you will see more than a
few questions on the test that relate directly to this chapter.
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Layer 2 Switching Technology.
Remember from earlier chapters that switches operate at Layer 2 of the Open
Systems Interconnection (OSI) model.
Cisco has applied switching technology to some of their Layer 3 and Layer 4
products. Because of this, you will sometimes hear people refer to Layer 3 and
Layer 4 switches. The CCNA exam, however, only covers Layer 2 switches.
Therefore, when you see the term "switch," assume it is a Layer 2 device.
The technology upon which Layer 2 switches operate is the same as that
provided by Ethernet bridges. The basic operation of a switch involves the
following:
Discovering Media Access Control (MAC) addresses
Filtering or forwarding frames
Preventing loops
Discovering MAC Addresses
Like a bridge, a switch monitors all frames that pass through it to learn the MAC
addresses of each device connected to its ports. This information is stored in a
database called a filter table. The switch consults the filter table each time it
receives a frame to determine whether to forward the frame to a different port or
to drop it.
When the switch is initially booted up, the filter table is empty. Forwarding or
filtering decisions cannot be made with an empty database, so initially each
incoming frame is forwarded through all the switch's ports. This is called flooding
the frame. As flooding occurs, the switch begins to learn the MAC addresses and
associate them with one of its ports.
This address-learning process is a continual operation of the switch. Each MAC
database entry is stored in memory and is valid only for a preset interval. If a new
frame does not refresh the entry, the entry is discarded.
Filtering and Forwarding
Each time the switch receives a frame, it examines the destination MAC address.
If this address exists in the MAC database, the frame is forwarded only through
the switch port associated with the address. This process frees all the segments
connected to different ports of the excess bandwidth taken by the frame. This is
known as frame filtering.
Whenever the destination MAC address is unknown, the frame is flooded to all
switch ports. This is undesirable because it wastes bandwidth.
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Preventing Loops
Both bridges and switches introduce the possibility of creating a bridged network
with multiple paths to a single destination. Typically, this type of redundancy is
considered favorable, but for switches and bridges it can cause problems in the
form of bridging loops, which occur when circular connections exist in a bridged
network. Figure 1 illustrates a bridged network with bridging loops.
Figure 1. Switches and bridges can create loops if improperly positioned.
Bridges and switches provide a bridging function. Although we will use the term
"bridge" in this discussion, the concept of bridging loops applies equally to
switches.
For example, if someone sends a broadcast message from segment 2, the
message would be forwarded to physical segment 3 by bridges B and C. Bridge
A would then receive two broadcasts and forward both broadcasts to physical
segment 1. Bridge D would have forwarded this broadcast to physical segment 1
as well. Subsequently, bridge D will receive the two broadcasts forwarded by
bridge A and forward these frames to physical segment 2. This continuous
forwarding of broadcast packets wastes bandwidth. With more complex bridged
networks, the broadcast packets can be forwarded exponentially, leading to what
is termed a broadcast storm. This occurs when so many broadcasts are being
continuously forwarded that they consume all the available bandwidth. The
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Spanning Tree Protocol, which implements an algorithm that removes all circular
connections in a bridged network, eliminates bridging loops.
Spanning Tree Protocol
The Spanning Tree Protocol creates a loop-free network topology by placing
connections that create loops in a blocking state. It is important to note that this
protocol does not eliminate loops but rather only blocks the connections that
create the loops. Loops in a network often provide needed redundancy in the
case of a physical connection being disconnected. The Spanning Tree Protocol
maintains the benefits of redundancy while eliminating the disadvantages of
looping. To illustrate how the Spanning Tree Protocol functions, we will use the
bridged network shown earlier in Figure 1.
The Spanning Tree Protocol selects a root bridge in the network (in this case,
bridge A).
Determining the Root Bridge
When a network using multiple bridges and spanning tree protocol starts, the
bridges automatically broadcast their ID numbers. The ID number is actually a
combination of the MAC address and an assigned priority value. In most cases,
the bridge with the lowest priority number assumes the role of root bridge. If two
or more bridges have the same priority number, the one with the lowest MAC
address becomes the root bridge.
Next, every other bridge selects one of its ports with the least path cost to the
root bridge. The least path cost is the sum of the cost to traverse every network
between the indicated bridge and the root bridge. The root path cost can be
determined in multiple ways; in this case, we have arbitrarily assigned costs to
each path. Next, designated bridges are determined. A designated bridge is the
bridge on each LAN with the lowest aggregate root path cost. It's the only bridge
on a LAN allowed to forward frames. Figure 2 illustrates our network with the root
path cost assigned to each bridge interface.
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Figure 2. The root path cost for each bridge interface.
By applying the Spanning Tree Protocol, we block the connection between bridge
C and physical segments 2 and 3, because bridge D and bridge B both have
lower aggregate root path costs to the root bridge (bridge A). We also block the
connection between bridge D and physical segment 2, because bridge B has a
lower root path cost than bridge D. Figure 3 illustrates our bridged network after
the Spanning Tree Protocol has been applied. Note that the connections
between bridge C and physical segments 2 and 3 are blocked, as well as the
connection between bridge D and physical segment 2.
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Figure 3. A bridged network with Spanning Tree Protocol.
We now have no circular routes in our network, but we maintain redundancy,
because the Spanning Tree Protocol is applied whenever a bridge is powered up
or a topology change occurs. Therefore, if the connection between bridge B and
physical segment 2 is broken, the Spanning Tree Protocol would run and the
connection between bridge D and physical segment 2.
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Cisco LAN Switching Methods.
All the switching methods used by Cisco switches provide increased throughput
in comparison to bridges. The hardware-based architectures of switches allow
them to make decisions at wire speeds. The primary difference between the
various methods is the process each uses to switch frames.
Frames have been consistently used to represent Layer 2 data messages in this
chapter. The term cells can also be used to identify Layer 2 data messages. This
term is used when referring to data traffic using the Asynchronous Transfer Mode
(ATM) technology. The CCNA exam does not cover this technology, so only
frames have been presented in this chapter to simplify the concepts.
Store-and-Forward Switching
In store-and-forward switching mode, the switch reads the entire incoming frame
and copies the frame into its buffers. After the frame has been completely read,
the switch performs the Layer 2 cyclical redundancy check (CRC) to determine
whether an error occurred during transmission. If the frame has an error, the
switch drops the frame. If no error is identified, the switch checks its forwarding
table to determine the proper port (in the case of a unicast) or ports (in the case
of a multicast) to which the frame must be forwarded.
Store-and-forward switches have the highest latency of any switching mode,
because the switch must read the entire frame before making a forwarding
decision. The added error checking of store-and-forward switching, however,
reduces the number of erred frames that are forwarded.
Cut-Through Switching
Cut-through switches introduce a lower level of latency during the switching
process than store-and-forward switches do, mainly because the frame is
forwarded as soon as the destination address and outgoing interface are
determined. They achieve increased performance by eliminating the error
checking and making forwarding decisions based only on the first six bytes of the
incoming frame. (These first six bytes contain the destination MAC address of the
frame.) Cut-through switches read the destination address of the incoming frame
and immediately check the forwarding table to determine the proper destination
ports. This increased performance does, however, allow erred frames to be
forwarded more often than store-and-forward switches do.
Fragment-Free Switching
Fragment-free switching is a modification to the cut-through switching method.
Like cut-through switches, fragment-free switches read only a portion of the
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free switches read the first 64 bytes, which is enough to check the frame for
collisions. This allows for better error checking than with cut-through switches,
with a minimal loss in latency.
TIP:
Cisco has incorporated switching technology into devices operating at layers
other than Layer 2. Be very careful when answering exam questions to determine
how the term "switch" is used. The features and functions we are presenting in
this chapter apply to Cisco layer two switches exclusively.
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Virtual Local Area Networks (VLANs).
A VLAN is a group of switched ports that acts as a separate, isolated LAN. There
can be several VLANs defined on a single switch (see Figure 4). A VLAN can
also span multiple switches. Workstations in separate VLANs will never
encounter traffic from or share bandwidth with other VLANs unless the data is
routed. In other words, a router or switch with routing capabilities is required if
devices on different VLANs need to communicate. It should be noted that VLAN
configuration is done through the switch and its software.
Figure 4. This figure shows a 12-port switch that has been divided into two
VLANs. Ports 1 through 6 are VLAN 1, and ports 7 through 12 are VLAN 2.
Remember from earlier chapters that one of the main benefits to switches is that
they segment a network into many collision domains. Each port represents a
single collision domain, and devices share bandwidth only with other devices on
the same switch port. Unless a switch is segmented into VLANs, however, all the
devices on the switch are still in the same broadcast domain; that is, all
broadcasts are sent to each port throughout the switching fabric.
VLANs introduce a way to limit the broadcast traffic in a switched network (a job
normally associated with routers). When you create a VLAN by defining which
ports belong to it, you are really just creating a boundary for broadcast traffic.
This has the effect of creating multiple, isolated LANs on a single switch.
TIP:
It is important to understand the need for routers in a switched network. If
devices on different VLANs need to communicate, routing is required to facilitate
this exchange of data. Many of today's network systems are collections of routers
and switches.
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What happens when a device on one VLAN needs to communicate with a device
on another VLAN? Because a VLAN is a closed Layer 2 network, traffic must
cross a Layer 3 device to communicate with other VLANs.
This means a router is required to facilitate the exchange of packets between
VLANs.
It is possible for a device to participate in more than one VLAN by using a special
type of network card that performs ISL, which is discussed later in this chapter.
The real benefit to using VLANs is that they can span multiple switches. Figure 5
shows two switches that are configured to share VLAN information.
Figure 5. VLANS can span multiple switches.
A large campus network may have hundreds of switches spread throughout
several buildings. Users can be put on the appropriate VLANs easily, no matter
where they are physically located. Users on the same VLAN do not have to be
connected to the same device. Therefore, LANs are no longer tied to the physical
location of users but rather can be assigned based on department, functional
area, or security level. By isolating users according to department or functional
area, network administrators can keep the majority of data traffic within one
VLAN, thereby maximizing the amount of traffic switched at hardware speeds
versus what is routed at slower software speeds.
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The ability to assign a user to a VLAN on a port-by-port basis makes adding,
moving, or deleting users simple. For example, let's say a user changes from the
accounting department to the marketing department. If the network administrator
designed the network and VLANs by functional department, this user would have
changed VLANs. To accommodate this change, the administrator only has to
make a software configuration change in the switch by assigning that user's port
to the new VLAN.
In addition, VLANs provide the flexibility necessary to group users by security
level. This can greatly simplify applying a security policy to a network. In
summary, here are the benefits of VLANs:
 They simplify security administration.
 They allow users to be grouped by functional area versus physical
location.
 They simplify moving and adding users.
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Frame Tagging
Frame tagging is the method used by Cisco switches to identify to which VLAN a
frame belongs. As a frame enters the switch, the switch encapsulates the frame
with a header that "tags" the frame with a VLAN ID. Any time a frame needs to
leave one switch for another, the tagged frame is sent throughout the switching
fabric. When the frame arrives at the destination switch, the tag tells the switch to
which VLAN the frame belongs. This process is illustrated in Figure 6 using the
VLAN IDs 10, 20, and 30.
Figure 6. Frame tagging in a VLAN environment.
The tag is stripped off of the frame before the frame is sent out to the destination
device. This process gives the illusion that all ports are physically connected to
the same switch.
TIP:
Be sure to understand the function of frame tagging, which "tags" a frame with a
user-defined VLAN ID.
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Trunk Connections.
Under normal circumstances, a switch port can carry traffic for a single VLAN
only. For VLANs to span multiple switches, a trunk connection must be created.
This trunk connection transports data from multiple VLANs. Trunk connections
allow VLANs to be used throughout the switching fabric of large networks.
Any Fast Ethernet or Asynchronous Transfer Mode (ATM) port on a switch can
be designated as a trunk port. This port typically connects to another switch via a
crossover 100BASE-T cable in the case of a Fast Ethernet trunk.
For the trunked port to transport multiple VLANs, it must understand frame tags.
Interswitch Link (ISL)
ISL is a technology developed by Cisco that allows a single Ethernet interface to
participate in multiple VLANs. When a trunk connection is made on a Catalyst
switch's Ethernet port, ISL is used. ISL is also available on Ethernet cards that
can be used in servers or routers.
A device utilizing an ISL Ethernet card will appear to have many physical cards,
each connected to a different segment. ISL allows this single Ethernet card to
have many logical (virtual) addresses. The user must configure each logical
interface with an address that reflects the VLAN to which it belongs.
ISL works by allowing the frame-tagging information to be passed along to the
Ethernet card. The Ethernet card then reads the frame tag, which identifies the
VLAN to which the frame belongs. Conversely, the ISL Ethernet card creates the
frame tags when transmitting frames.
ISL is a technology proprietary to Cisco and, therefore, is not supported on
equipment made by other vendors. However, in mid-1998, the Institute of
Electrical and Electronics Engineers (IEEE) standardized a frame-tagging
process similar to Cisco's ISL. The new standard is a protocol called 802.1Q.
With 802.1Q, switches from multiple vendors can coexist in the same switching
fabric.
VLAN Trunking Protocol (VTP)
VTP is a protocol used between switches to simplify the management of VLANs.
Configuration changes that are made to a VTP server are propagated across
trunks to all connected switches.
All switches that are to be managed in this way must be members of the same
management domain. A VTP management domain is the entire group of
switches that share configuration information.
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For example, when you add a new VLAN to a member switch, the VLAN is
available in all the network switches automatically. VTP allows switched networks
to scale to larger environments; otherwise, VLAN configuration would have to be
maintained manually on individual switches.
By default, Catalyst switches are set to a no-management-domain state. The
switches remain in a no-management state until a user configures the
management domain or the switches receive an advertisement for a domain over
a trunk link.
VTP Modes
When it has a management domain, a switch operates in one of three VTP
modes: server, client, or transparent. The default mode is server.
In VTP server mode, a switch can create, modify, or delete VLAN and other
configuration parameters for the entire VTP domain. VTP messages are sent
over all trunk links, and configuration changes are propagated to all switches in
the management domain.
In VTP client mode, the switch receives VTP messages and applies configuration
changes made from any VTP server. However, a client cannot create, change, or
delete VLAN information.
In VTP transparent mode, the switch forwards all VTP messages to other
switches in the domain but does not use the configuration from VTP
advertisements. A VTP transparent switch can create, modify, or delete VLANs,
but the changes apply only locally and are not transmitted to other switches.
VTP Pruning
VTP can detect whether a trunk connection is carrying unnecessary traffic. By
default, all trunk connections carry traffic from all VLANs in the management
domain. In many cases, however, a switch does not need a local port configured
for each VLAN. In this event, it is not necessary to flood traffic from VLANs other
than the ones supported by that switch (see Figure 7). VTP pruning enables the
switching fabric to prevent flooding traffic on trunk ports that do not need it.
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Figure 7. VTP pruning.
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Configuring VLANs.
Three methods can be used to assign a switch port to a particular VLAN: portcentric, static, and dynamic. In a port-centric configuration, all nodes that are
connected to ports within the same VLAN are given the same VLAN ID. In this
type of configuration, the network administrator's job is much easier because of
the ease of administering the VLAN. In a static VLAN configuration, the ports on
a switch are hard-coded and remain in effect until the administrator changes
them. This type of configuration is typical of a network that is very well monitored
and where changes are unlikely. The third type of port configuration is dynamic.
This type of configuration involves more overhead on setup for the administrator
because of the database configuration. The ports on these switches
automatically determine their assigned VLAN. The VLAN assignment is
determined by the type of protocol (within a frame), MAC address, and logical
addressing. A major benefit of this type of configuration is that the administrator
will notice when any unauthorized or new user is on the network. If a workstation
happens to be connected to a port that is unassigned, the switch will record the
MAC address of the workstation and check its database to determine which
VLAN to assign the workstation to.
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Exam Prep Questions
1.
What is maintained in a switch's forwarding table?
A. A device's IP address and the IP network on which the device
resides
B. A device's MAC address and the physical segment on which that
device resides
C. The MAC addresses and the best interfaces to use to forward a
frame to a destination MAC address
D. The IP network and MAC address of devices
A1:
The correct answer is C. Forwarding tables maintain MAC addresses.
In addition, forwarding tables maintain the best interfaces to use to
forward a frame to a destination MAC address. Answer A is incorrect
because a bridge does not maintain IP addresses in its forwarding
table. IP is a Layer 3 protocol and is used by routers, not bridges.
Answer B is a trick answer because it is partially correct. However,
bridges do not maintain the physical segment on which a device
resides. Bridges only maintain the next physical segment to forward a
frame en route to the device's physical segment. In some cases, the
device will exist on this physical segment, but not in all cases. Answer D
is incorrect because bridges do not maintain IP network information.
2.
What is the name of the protocol used to eliminate loops?
A. Switching
B. ISL
C. Frame tagging
D. Spanning Tree Protocol
A2:
The correct answer is D. The Spanning Tree Protocol is used to remove
circular routes in bridged and switched networks. Answer A is incorrect
because switching is a Layer 2 technology, not a protocol. Answer B is
incorrect because interswitch link (ISL) is used to allow VLANs to span
multiple physical switches. Answer C is incorrect because frame
tagging is a process used to identify the VLAN of a frame between
switches.
3.
Which of the following switching methods provides the greatest frame
throughput?
A. Store-and-forward switching
B. Frame-tag switching
C. Cut-through switching
D. ISL switching
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A3:
The correct answer is C. Cut-through switching provides highthroughput frame switching because it reads only a portion of the frame
before making the forwarding decision. Cut-through switching does not
provide error checking. Answer A is incorrect because store-andforward switching has slower frame throughput rates than cut-through
switching because of its error-checking capabilities and because it
reads the entire frame before making a forwarding decision. Answer B
is incorrect because frame-tag switching does not exist; frame tagging
is a process used to identify a frame's VLAN between switches. Answer
D is incorrect because it is used to allow VLANs to span multiple
switches as well.
4.
Which of the following are advantages of VLANs? (Choose the two best
answers.)
A. They reduce switching overhead.
B. They increase switching throughput.
C. They simplify the adding, moving, and changing of users.
D. They allow users to be grouped by functional area, not physical
location.
A4:
The correct answers are C and D. VLANs increase the flexibility of
assigning users to LANs. This increased simplicity allows users to be
grouped by functional area rather than physical location, because
VLANs can span multiple switches. Answer A is incorrect because
VLANs do not reduce the amount of overhead required to switch a
frame. Answer B is incorrect because VLANs do not provide any
increased switching throughput.
5.
What must you do to allow a VLAN to span two or more switches?
A. Set up a VTP domain.
B. Set up a trunk connection.
C. Configure the duplex setting on the ports.
D. Configure port security on the switch.
A5:
The correct answer is B. A trunk connection must be established in
order for a VLAN to span multiple switches. Trunk ports recognize
frame tags and are therefore able to carry information on multiple
VLANs. Answer A is incorrect because a VTP domain is not necessary
for switches to share VLAN information. Answer C is incorrect because
the duplex setting does not have to be configured manually to connect
two switches. Answer D is incorrect because port security is not
necessary for a VLAN to span switches.
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6.
Which of the following are advantages of using VTP in a switching
environment? (Choose the two best answers.)
A. It enables VLANs to span multiple switches.
B. It simplifies the management of VLANs.
C. It simplifies the scalability of the switched network.
D. It allows switches to read frame tags.
A6:
The correct answers are B and C. VTP simplifies the management of
VLANs because configuration information is propagated automatically
throughout the switching fabric when changes are made. Without VTP,
each switch would have to be configured manually; therefore, VTP
makes it easier to scale to a larger switched environment. Answer A is
incorrect because VTP is not necessary for VLANs to span multiple
switches. Answer D is incorrect because VTP does not allow the switch
to read frame tags.
7.
What is ISL used for?
A. To allow an Ethernet interface to understand frame tags
B. To make two Ethernet interfaces appear as one
C. To connect an Ethernet switch with a high-speed core switch such as
ATM
D. To allow simultaneous routing and switching
A7:
The correct answer is A. ISL allows an Ethernet interface to understand
frame tags, which identify the VLAN to which a packet belongs. For this
reason, an ISL interface can participate in multiple VLANs, which is
necessary for a trunk connection. Answer B is incorrect because ISL
can actually have the opposite effect of this—a single Ethernet interface
may appear to be several by having multiple Layer 3 addresses.
Answers C and D are incorrect because these are not functions of ISL.
8.
What is the purpose of VTP pruning?
A. To detect loops in the switching fabric
B. To disable a trunk connection that creates a bridging loop
C. To simplify the management of VLANs
D. To prevent flooding unnecessary traffic across trunk connections
A8:
The correct answer is D. VTP pruning is used to prevent flooding of
unnecessary traffic across trunk connections. Answer A is incorrect
because this is a function of the Spanning Tree Protocol. Answer B is
incorrect because this is not the purpose of VTP pruning. Answer C is
incorrect because this is the purpose of the VTP, not VTP pruning.
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9.
When a network has multiple bridges and is using Spanning Tree
Protocol, how is the root bridge determined?
A. The first bridge to initiate service becomes the root bridge.
B. The bridge with the lowest ID number assumes the root bridge role.
C. The bridge with the lowest MAC address is always the root bridge.
D. The bridge with the highest serial number is the root bridge.
A9:
The correct answer is B. The bridge's ID number is a combination of its
MAC address and its assigned priority number. The bridges broadcast
their ID numbers and the one with the lowest ID becomes the root. If
two bridges have the same priority number then the one with the lower
MAC address becomes the root. Answer A is not correct because the
first bridge to enter service may or may not be an appropriate root
bridge. C is incorrect because the root bridge is determined ID number,
which is a combination of the MAC address and priority number.
Answer D is incorrect for the same reason.
10.
A network administrator wants to pass traffic between two VLANs on
the same switch. What will he need to accomplish this?
A. Nothing. If VLANs are on the same switch, the administrator can
simply turn on cross filtering by MAC address.
B. A bridge running Spanning Tree Protocol.
C. A router.
D. A second switch connecting the two VLANs.
A10:
Answer C is correct. A router is required for two VLANs to pass traffic,
even if they are on the same switch. Answer A is incorrect because
there is no cross filtering option on a Layer 2 switch. Answer B is
incorrect because a single bridge in this configuration would pass all
traffic between the two VLANs, negating the entire purpose of the
VLANs. The spanning tree protocol would make no difference where
only one bridge is employed. Answer D is incorrect for the same reason
answer B is incorrect.
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Chapter 7.
Cisco Layer 3 Routing
Terms you'll need to understand:








Routing protocols
Routing algorithms
Distance vector
Link state
Network discovery
Routing metrics
RIP
IGRP
Techniques you'll need to master:
 Understand path determination
 Determine strengths of link state and distance vector protocols in differing
configurations
 Describe ways of increasing stability of link state and distance vector
protocols
 Describe the goals of routing protocols
 List routing protocols and path determination
 Describe convergence as impacted by different protocols
 Be able to compare and contrast the following types of routing protocols:
 Static versus dynamic
 Single path versus multi-path
 Flat versus hierarchical
 Interior versus exterior
 Distance vector versus link state
Now that you have mastered the art of IP addressing and subnetting, it is time to
take you to a new level: the wonderful world of routing. Cisco is a company that
has the world's most famous routers, but you already know that and this is why
you want to be successful when taking your CCNA exams. In a nutshell, routing
occurs in the Network layer (Layer 3) of the OSI reference model. By sending
packets from the source network to the destination network, the Network layer
gives its best effort in the delivery of end-to-end services. In this chapter we will
be describing the intricacies of that process.
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Routing Activities.
Getting packets to their next hop requires a router to perform two basic activities:
path determination and packet switching. These activities are very basic, but you
need to have a thorough understanding of how they are accomplished.
Path determination involves reviewing all available paths to a destination network
and choosing the optimal route on which to send a packet. Network topology
information used to determine optimal routes is collected and stored in routing
tables, which contain information such as the destination network, the next hop,
and an associated metric (the cost of sending packets to that next hop).
Packet Switching involves changing a packet's physical destination address to
that of the next hop. However, the packet's destination logical address remains
constant during the packet-switching process.
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Routing Algorithms and Protocols.
Routers choose the optimal or best route based on the available route
information. A routing algorithm aids in the collection of route information and the
determination of the best path. These algorithms may vary in several aspects.
They may differ based on the goals they were designed to achieve within an
internetwork. In addition, several types of routing algorithms exist to suit specific
internetwork requirements. The metrics used by different routing algorithms also
vary.
A routing protocol is a standard method of implementing a particular routing
algorithm. For the purpose of our discussions, routing protocols mean the routing
algorithms or the protocols that implement them. Please do not confuse them
with routed protocols; they are very different.
Goals of Routing Protocols.
Technology and internetworks change on a regular basis and because of this
change, new needs arise and thus new routing protocols are created. For
example, a routing protocol that functioned well in a small internetwork two years
ago may certainly experience problems in the large internetworks in use today.
Routing protocols have been designed to meet one or more of the following
design goals:
 Flexibility
 Optimization
 Rapid convergence
 Robustness
 Simplicity
Flexibility
A routing protocol has to be flexible. It should be able to adapt quickly to its everchanging network environment. If a network segment goes down, a flexible
routing protocol is able to detect that event and determine the next best path to
use while the segment is down. When the network segment becomes available,
the routing protocol should also update its route table to reflect that event.
Flexible routing protocols can also adapt to changes in network variables, such
as network bandwidth and delay.
Optimization
The optimization of a routing protocol gauges its capability to choose the best
route correctly. The metrics used by the protocol affect its optimality. For
example, one protocol may heavily weight the number of hops as its metric,
whereas another may use a combination of a number of hops and network delay.
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Rapid Convergence.
Convergence occurs when all routers within an internetwork agree on the optimal
routes through the internetwork. In other words, an update has been
disseminated throughout the internetwork and all routers are working with the
same updated table.
Network events, such as routes going down or becoming available, cause routers
to recalculate optimal paths and distribute update messages about network
routes. These messages permeate the entire network until all routes converge
and agree on optimal routes. Slow convergence of the routing protocol can cause
problems, such as a routing loop.
A routing loop occurs when two or more routers have not yet converged and are
broadcasting their inaccurate route tables. In addition, they are most likely still
switching packets based on their inaccurate route tables. Figure 1 illustrates this
case. An event has just occurred within the network—router A lost its path to
network 5. While router A is updating its route table, it receives an update from
router B that says network 5 is one hop away.
Figure 1. Illustration of a potential routing loop.
Router A increases the counter by 1 and adds this new information to its route
tables. In turn, router A broadcasts its updated route table to router C, which
updates its table and broadcasts the erroneous information to router D. Router D
updates its table and propagates the misinformation to router B.
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This cycle will continue ad infinitum. If packets traversing the network are
destined for network 5, they will loop between router A and router B until the
packet becomes too old and is discarded. Figure 2 illustrates this situation.
Figure 2. Illustration of the end result of a routing loop.
Robustness
Robust and stable routing protocols perform correctly during unusual and
unpredictable network events. High utilization, hardware failures, and incorrect
configurations can create significant problems within a network. A robust routing
protocol is stable during a variety of network situations.
Simplicity
The simplicity of a routing protocol refers to its ability to operate efficiently.
Because routing protocols collect and store route information, a protocol is
competing for the router's limited physical resources. A routing protocol must
perform its functions with minimal administrative overhead.
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Types of Routing Protocols
It is very common in technology reference materials for routing protocols to be
categorized by type. The type of routing protocol deployed within an internetwork
should be based on the organizational requirements.
Types of routing protocols include:
 Static or dynamic
 Single path or multipath
 Flat or hierarchical
 Interior or exterior
 Distance vector or link state
Static or Dynamic
A network administrator configures a static route manually. When defining a
static route, the administrator configures the destination network, next hop, and
appropriate metrics. The route does not change until the network administrator
changes it. Static routes function well in environments where the network is
simple and network traffic is predictable.
Dynamic routes change and adjust to changes within the internetwork
environment automatically. When network changes occur, routers begin to
converge by recalculating routes and distributing route updates. The routeupdate messages permeate the network, which causes more routers to
recalculate their routes. This route-update process continues until all routers
have converged.
Occasionally, static routes augment dynamic routes. In a dynamically routed
environment, a router discards a packet if the destination network does not
appear in the route table. To avoid this, a static route called a default route can
be configured. The default route points to a router that has been specifically
configured to receive and process packets that do not have routes listed in the
routing tables.
Single Path or Multipath
When calculating the optimal path for a particular network, some routing
protocols simply choose the best single path to a destination network. Others
allow more than one optimal path if the paths have equal metric values. A
multipath protocol enables traffic load-balancing using the multiple paths and
offers additional advantages over single-path protocols, such as reliability.
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Flat or Hierarchical
A routing environment is considered flat if all routers are peers to each other.
Routers that use a flat routing protocol may communicate with any other router in
the network as directly as possible. Like static routing, a flat routing protocol
functions well in simple and predictable network environments.
Alternatively, a hierarchical routing environment contains several routers that
compose a backbone. Most traffic from non-backbone routers usually traverses
the backbone routers (or at least travels to the backbone) in order to reach
another non-backbone router. Within a hierarchical routing environment,
autonomous systems (sometimes referred to as domains or areas) can be
established. Being part of the same autonomous system enables a group of
routers to share network topology information with each other, but that same
information is not shared outside the group. Although several layers or tiers may
exist within the hierarchy, the routers at the highest level comprise the backbone.
Cisco, as of publication of this book, is eager to promote a three-tier system. The
Cisco system has a backbone, distribution, and access layer. Equipment is being
manufactured and marketed according to these layers. The backbone must
provide the fastest throughput possible, without making any routing decisions (or
as few as possible). Those are high-end expensive and complex routers and
switches. Distribution level is where most of the routing is happening. Those are
mid-level boxes. Access level is where hosts are connected to the network, and
they are mostly 2000 series of switches and routers.
TIP:
While it is not very important to know the model numbers for the CCNA exam,
the three-level architecture that Cisco uses is a must-know for any Cisco test.
Typically, the network backbone comprises its own autonomous system or
domain.
Interior or Exterior
An interior routing protocol operates within a single autonomous system or
domain. These protocols are typically implemented within an organization's
private network. Routers that are running interior routing protocols are
considered Intradomain routers; they only need to know about other routers
within their domain. Conversely, an exterior routing protocol conveys routing
information between domains. Exterior routing protocols are in use within the
Internet. Interdomain routers need to know how to route traffic between
autonomous systems and can protect against errors or problems with one
domain affecting another.
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Distance Vector or Link State.
Distance vector protocols require each router to send all or a large part of its
route table to its neighboring routers. Link state protocols require each router to
send the state of its own interfaces to every router in the internetwork. Distance
vector protocols are simple and straightforward, but they converge slowly and
consume a significant amount of bandwidth because they have to send updates
every set amount of time, and they send entire tables as opposed to the updated
entries, which can cause routing loops. Link state protocols converge quickly, but
they require more of the router's central processing unit (CPU) and memory
resources.
Each routed protocol can be implemented in one or more routing protocols. The
routing protocols (or standard set of rules) actually enable the router to determine
the best path. Common routing protocols include:
 Routing Information Protocol (RIP)
 Interior Gateway Routing Protocol (IGRP)
 Open Shortest Path First (OSPF)
 Enhanced Interior Gateway Routing Protocol (EIGRP)
 Border Gateway Protocol (BGP)
 Exterior Gateway Protocol (EGP)
Table 1. Interior Routing Protocols.
Routing
Protocol
RIP
Static or SingleFlat
or
Dynamic
Path
or Hierarchical
Multipath
Dynamic
Single-path Flat
Interior
or
Exterior
Interior
IGRP
Dynamic
Multipath
Flat
Interior
OSPF
EIGRP
Dynamic
Dynamic
Multipath
Multipath
Hierarchical
Flat
Interior
Interior
Distance
Vector
or
Link State
Distance
vector
Distance
vector
Link state
Advanced
distance
vector
IGRP and EIGRP are Cisco proprietary routing protocols. They are only
supported on Cisco routers.
Routing Metrics
Routing protocols use many different metrics to determine the optimal route.
These variables can be used individually or in combination with one another to
create the metric defined within a given routing protocol.
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Metrics used in routing protocols include:
 Bandwidth
 Delay
 Load
 Path length or hops
 Reliability
Bandwidth
The available capacity of a network link is known as its bandwidth. Typically, a
10Mbps Ethernet link is preferable to a 56Kbps Frame Relay link. However, if
other metrics such as delay are considered, the Ethernet link may not be the
optimal path.
Delay
Network delay refers to the amount of time necessary to move a packet through
the internetwork from source to destination. Delay is a conglomeration of several
other variables, including physical distance between source and destination,
bandwidth and congestion of intermediate links, and port queues of intermediate
routers.
Load
Load is an indication of how busy a network resource is. CPU utilization and
packets processed per second are two valuable factors when calculating the
load.
Path Length
In some routing protocols, path length refers to the sum of the costs of each link
traversed up to the destination network. Other routing protocols refer to path
length as the hop count, which is the number of passes through a router that a
packet makes on its way to the destination network.
Reliability
This metric allows the network administrator to assign a numeric value arbitrarily
to indicate a reliability factor for the link. Some network links go down more than
others do; some are easily repaired and become available relatively quickly. The
reliability metric is simply a method used to capture an administrator's experience
with a given network link.
TIP:
A routed protocol such as IP is concerned with the movement of user traffic. A
routing protocol such as RIP or OSPF is concerned with maintaining route tables.
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Distance Vector Versus Link State.
This section highlights the similarities and differences between two types of
widely used routing protocols: distance vector and link state.
Distance Vector Overview
A distance vector routing protocol sends all or part of its route table across the
network, but only to its neighbors. The route table contains the distance and
direction to any network within its domain. Figure 3 provides an overview of the
distance vector process.
Figure 3. Illustration of the distance vector process.
Periodically, router A broadcasts its entire route table to its neighbors, router B
and router C. Router B updates the route information it received by increasing
the metric value, which is usually the hop count, by 1. Router B then compares
the route information it just received and updated with the existing route
information from its route table. Router B replaces existing route information with
an updated entry only if the updated route information has a lower calculated
metric. Router B then broadcasts its route table to its direct neighbors, router D
and router A. This process occurs regularly and in all directions for all directly
connected neighbors. Although this process enables routers to accumulate
network distance information, the routers do not know the network's exact
topology.
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Link State Overview.
A link state routing protocol (sometimes referred to as shortest path first) sends
only the state of its own network links across the network, but it sends this
information to every router within its domain. This process enables routers to
learn and maintain full knowledge of the network's exact topology and how it is
interconnected. Figure 4 provides an overview of the link state process.
Figure 4. Illustration of the link state process.
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Link state routing protocols rely on several components to acquire and maintain
knowledge of the network. The following process is typical of routers using a link
state protocol:
A router broadcasts and receives link state packets to and from other routers
via the network. Link state packets contain the status of a router's links or
network interfaces.
The router then builds a topology database of the network.
After building a topology database the router runs a Shortest Path First (SPF)
algorithm against the database to generate an SPF tree of the network,
with itself as the root of the tree.
Lastly, the router populates its route table with optimal paths and ports to
transmit data through to reach each network.
Network Discovery
When a router starts up, it must undergo a network discovery process, which
enables the router to begin communicating with other routers on the network.
Figure 5 illustrates the network discovery process for distance vector protocols.
Router A has just started up and is configured to run a distance vector.
Figure 5. Illustration of the network discovery process.
Router A begins the discovery process by identifying its neighbor, router B.
Router A begins populating its route table with its directly connected networks,
networks 1 and 2, which receive a metric of 0. It passes its route table to router B
and receives router B's entire route table. Router A increases the distances of
each entry by one hop. After the distances have been updated, router A will
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already have better routes to networks 1 and 2, but not network 3. Router A
increases the distance to network 3 by one hop and stores this in its route table.
The network discovery process for link state protocols is similar to that of
distance vector protocols. Instead of route tables, routers exchange link state
packets and use that information to build their topology databases, SPF trees,
and route tables.
Regardless of whether a router uses a distance vector or link state routing
protocol, the router dynamically discovers its network environment. It can then
use its route table to perform the packet-switching function.
Topology Changes.
After the router has discovered the network, it must also keep up with network
topology changes. Depending on the protocol used, a router transmits route
information periodically or when a network event occurs. Routers detect changes
in the network topology via these updates.
Most distance vector protocols handle topology changes through regularly
scheduled updates. After a specified interval, a router broadcasts its route table
to its neighbor. Route recalculation occurs, if necessary, and updates in the
network topology are broadcast. The route distribution timers are not
synchronized across routers.
Link state protocols rely on network events to address topology changes. If a
router detects a network event (such as one of its neighbors is no longer
reachable or a new neighbor appears), it triggers an update. The router
broadcasts the state of its links to all other routers within the domain. Upon
receiving the update, other routers update their topology database and broadcast
the state of their links also. When all updates have been received, each router
updates its SPF tree and route tables accordingly. At this point, the network has
converged. Event-triggered updates have a ripple effect within a network.
Distance Vector Problems
The fact that route updates with a distance vector protocol occur after a specified
interval can become problematic. With RIP, route updates are broadcast every
30 seconds by default. As a result, distance vector protocols converge slowly.
Routing loops and the problems they create were discussed previously in this
chapter. Routing loops create a condition known as counting to infinity, where
the distance metric is continually increased because the network has not fully
converged.
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Distance Vector Remedies.
One technique to remedy a count-to-infinity situation involves a maximum hop
count. Although this count will not prevent a routing loop, it does reduce the time
that the routing loop exists. A maximum hop count, when reached, forces a
router to mark a network unreachable rather than increase the distance metric.
Routing loops also occur when information that contradicts information sent
previously is broadcast back to a router. Router A sends information about
network 5 to router B. Split horizon prevents a router from sending information it
received about a network back to the neighbor that originally sent the
information. For example, split horizon prohibits router B and router C from
sending any information about network 5 back to router A.
Route poisoning occurs when a router detects that a network is down and
immediately marks it as unreachable. This route update is broadcast throughout
the network. While the other routers slowly converge, the router maintains this
poisoned route in its route table and ignores updates from other routers about
better routes to the network. The poisoned route is removed after several update
cycles. Route poisoning works well with hold-down timers.
A hold-down timer indicates that no updates to a particular route should be
accepted until the timer expires. A hold-down condition is triggered when a router
receives an update from its neighbor indicating that a reachable network has just
gone down. The router marks the network as unreachable and starts its holddown timer. While the timer is active, updates from any other router are ignored.
Updates about the unreachable network are accepted only from the neighboring
router that initially indicated the unreachable network while the timer is active. If
the neighboring router indicates that the network is reachable again, the router
stops the hold-down timer and updates its route table. When the hold-down timer
expires, the router marks the network reachable and receives updates from any
router.
Link State Problems
Because link state routing protocols have knowledge of the entire network and
converge quickly, they do not suffer from the same problems as distance vector
protocols. One problem that affects link state protocols is the significant memory
and processor resources required from the router itself when acquiring and
maintaining full knowledge of large networks. As updates move through the
network, each router must receive the update, recalculate its information, and
send its own link information. Of course, this type of overhead affects the ability
of the router to move user data packets through the network.
A second shortcoming of link state protocols is the amount of network bandwidth
that can be consumed while the network converges. Routers flood updates about
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the state of their links to every other router in the network, so the amount of
bandwidth consumed is significant. As routers collect link information from each
other, the amount of bandwidth available for end-user communications is
reduced. This high level of bandwidth utilization typically occurs on initialization of
the network or when several routers start up simultaneously.
Additional problems can occur during the link state update process itself. It is
imperative that each router receive all the packets in a timely manner and that
the updates are synchronized. For example, if one part of the network receives
route information before another part, convergence may take longer, or SPF
trees and route tables may store inaccurate information. Additionally, as routers
attempt to move link state packets through the network, they may be doing so
without fully constructed SPF trees or route tables.
Link State Remedies
One remedy for link state problems involves minimizing the resources required to
build and maintain route tables. The time between periodic updates can be
lengthened to reduce the processing resources required. Also, routers can be
identified to serve as border routers. The border routers can then exchange route
summaries with other border routers and each core router to reduce the
bandwidth consumed during the update process, and to isolate update processes
to hierarchical areas. The border router then passes updates to the routers within
its area.
Another technique involves coordinating link state updates. Timestamps and
sequence numbers can be attached to the link state packet. Routers then realize
when they receive inaccurate or old link state packets.
The following techniques help to stabilize link state protocols:
Minimize router resource usage by lengthening the update frequency or
exchanging route summaries.
Coordinate updates with timestamps or sequence numbers.
Both distance vector and link state routing protocols have demonstrated their
worth over time. Each has advantages that may suit a particular network design
perfectly. Several factors must be considered when choosing a routing protocol,
including business policies and operational issues. Table 2 provides a quick
comparison of distance vector and link state routing protocols.
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Table 2. Distance Vector Versus Link State Routing Protocols
Distance Vector
Link State
Sees the network from its neighbor's Sees the entire network from its own
perspective
perspective
Distance metrics accumulate from Calculates shortest path to other routers
router to router
Route updates occur periodically
Route updates are event-triggered
Convergence is slow
Convergence is fast
Broadcasts entire route table to Broadcasts link status information to all
neighbors
other routers
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Exam Prep Questions
1.
Which of the following are basic functions of a router? (Choose the two
best answers.)
A. Packet switching
B. Packet filtering
C. Path determination
D. Rapid convergence
A1:
The correct answers are A and C. Routers packet switch when they
have determined the best path. Path determination is the process of
choosing the best network path from all available network paths. Packet
filtering is a technique used to control inbound and/or outbound packets
to or from a router. Therefore, answer B is incorrect. Rapid
convergence is a design goal of some routing protocols. Therefore,
answer D is incorrect.
2.
Network routing information distributed among routers is stored in which
of the following?
A. Flash memory
B. Route table
C. Metric table
D. NVRAM
A2:
The correct answer is B. Route tables contain information about
destination networks and the next hop along the optimal path to get
there. Flash memory contains the operating system images used by the
router. Therefore, answer A is incorrect. Metric information is contained
within a router's route table. Therefore, answer C is incorrect. NVRAM
contains the router's active configuration files. Therefore, answer D is
incorrect.
3.
Which of the following conditions is a problem experienced by distance
vector routing protocols?
A. Split horizon
B. Route poisoning
C. Counting to infinity
D. Maximum hop count
E. Hold-down timers
A3:
The correct answer is C. Counting to infinity can result from the slow
convergence inherent in distance vector protocols. Split horizon, route
poisoning, maximum hop count, and hold-down timers are
techniques/items used to reduce the occurrence and impact of the
counting-to-infinity situation. Therefore, answers A, B, D, and E are
incorrect.
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4.
Which of the following routing protocols communicates route
information by sending the state of its links to all routers in its domain?
A. BGP
B. OSPF
C. IGRP
D. RIP
A4:
Answer B is correct. The question is describing a link state protocol and
OSPF is an excellent example. Both RIP and IGRP are distance vector
protocols, so answers C and D are incorrect. BGP is an exterior routing
protocol optimized for passing routing information between domains.
Therefore answer A is correct.
5.
Which of the following help to mitigate the shortcomings of link state
protocols? (Choose the two best answers.)
A. Maximum hop count
B. Minimize router resource usage
C. Coordinate updates
D. Route poisoning
A5:
The correct answers are B and C. Lengthening the update frequency or
exchanging router summaries at specific border routers helps to
minimize router resource usage. Therefore, answer B is correct. Also,
attaching timestamps or sequence numbers on link state packets helps
to coordinate update information between routers. Therefore, answer C
is correct. A maximum hop count and route poisoning address problems
with distance vector protocols. Therefore, answers A and D are
incorrect.
6.
Which of the following are not problems inherent to link state routing
protocols? (Choose two.)
A. High router resource usage
B. Split horizon
C. High network bandwidth consumption
D. Hold-down timers
E. Unsynchronized updates
A6:
The answer is B and D. Split horizons and hold down timers are
techniques used to reduce problems in distance vector protocols. High
network bandwidth usage and router resource usage are typical of link
state protocols when packets are flooding the network during
convergence. Therefore, answers C and A are not correct. If link state
updates are not synchronized inaccurate SPF trees and route tables
can result. This would make answer E incorrect.
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7.
A friend of yours is implementing a "Just in Time" inventory policy and
linking her company network to the networks of several suppliers.
Based on just this information, which of the following protocols would
you recommend using?
A. EIGRP
B. OSPF
C. BGP
D. IP
A7:
Answer C is correct. The key to this question is your friend's decision to
connect autonomous domains. Exterior routing protocols are optimized
for this task and the only exterior routing protocol available is answer C,
Border Gateway Protocol (BGP). Answers A and B are incorrect
because they are interior routing protocols. Answer D is incorrect
because IP is a routable protocol, not a routing protocol.
8.
A large company network is operating at or near capacity. The
administrator is about to change routing protocols from EIGRP to OSPF
to gain the additional efficacies of a hierarchical protocol. Based on just
this information, is this a good idea?
A. Yes, EIGRP is a flat routing protocol and not optimized for large
implementations.
B. Yes, a multipath routing protocol would balance loads in a saturated
network and better utilize the bandwidth available.
C. No, OSPF typically uses more bandwidth and processor power than
EIGRP.
D. No, a hierarchical routing protocol is not efficient.
A8:
The correct answer is C. OSPF is a link state routing protocol. Link
state protocols are notorious for using large amounts of bandwidth and
processor power when coming to convergence. When a network is
running at or near capacity, bandwidth and processor power are usually
not available. Therefore, transitioning from a distance vector protocol
like EIGRP, which uses bandwidth and processing power efficiently, to
a link state protocol like OSPF would not be advisable in this situation.
Answers A, B, and D are incorrect for the same reason.
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9.
Why is IP one of the most popular routing protocols available?
A. IP provides a flexible addressing structure that is highly scalable.
B. IP is the routing protocol of the Internet. As such, its use reduces
compatibility issues faced by other routing protocols.
C. IP uses a four-layer process which is more efficient than the OSI's
seven-layer process.
D. None of the above.
A9:
Answer D is correct. IP is not a routing protocol. It is a routable protocol.
Therefore, A, B, and C are incorrect and answer D is the only
acceptable option.
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PART TWO:
Interconnecting Cisco Networking
Devices
(Exam 640.811)
CHAPTER 8.
HARDWARE CONFIGURATION
Terms you'll need to understand:











Random Access Memory (RAM)
Non Volatile Random Access Memory (NVRAM)
Read-only memory (ROM)
Flash electrically erasable programmable memory (flash memory or flash
EEPROM)
Startup configuration file
Running configuration file
User mode
Privileged mode
Global configuration mode
Setup mode
Rxboot mode
Techniques you'll need to master:




Connecting to routers
Learning the startup sequence
Understanding the update process
Understanding the configuration change process
Although Cisco has added many products and technologies through acquisition,
they do attempt to maintain a uniform philosophy of design. Nowhere is this
philosophy more pronounced than in their core product area of routers. This is a
very short, but important chapter because it covers the operational design of
Cisco routers. You will be expected to know each memory area, the type of
memory used, and the function of programs stored in that memory region. You
will also need to know which operational mode provides access to a given region
or function.
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Router Memory Components
Cisco routers utilize four different types of memory, with each type providing
different functions. RAM, NVRAM, Flash memory, and ROM are the four types of
memory used. Their functions are discussed in the following sections (see Figure
1).
Figure 1. Standard memory configuration for a Cisco router.
RAM
RAM serves as a working storage area for the router and contains data such as
routing tables, various types of cache and buffers, as well as input and output
queues. RAM also provides temporary memory for the router's active IOS and
configuration file (the running configuration file). However, all the contents of
RAM are lost if the router is powered down or restarted.
NVRAM
Unlike RAM, nonvolatile RAM (NVRAM) retains its contents when the router is
powered down or restarted. NVRAM stores permanent information, such as the
router's backup configuration file. The startup configuration file is retrieved from
NVRAM during startup, at which time it is loaded into RAM.
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Flash
Flash memory stores the Cisco IOS image and associated microcode. Flash
memory is erasable, electronically reprogrammable ROM that retains its contents
when the router is powered down or restarted. Flash memory allows software to
be upgraded without chips being added, removed, or replaced.
ROM
Like Flash memory, ROM contains a version of IOS—usually an older version
with minimal functionality. It also stores the bootstrap program and power-on
diagnostic programs. However, software upgrades can be performed only by
replacing the ROM chip.
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Types of Configuration Files
Cisco IOS software uses and requires a configuration file to determine how a
router is to function. Typically, network administrators enter the commands
needed by the configuration file. Only two types of configuration files exist for the
context of the CCNA exam:
 The running configuration file exists in RAM and contains the commands
that Cisco IOS uses to drive the actions of the router.
 The startup configuration file exists in NVRAM and is the backup for the
running configuration file. Startup configuration files reside in NVRAM;
running configuration files exist in RAM.
As noted previously, RAM is erased when a router is powered down. Therefore,
the running configuration file is erased as well
The router will always use the running configuration file to execute. However, any
time a router is restarted (cycling power or reloading the software), the running
configuration file is erased and the startup configuration file is the only remaining
configuration file. Therefore, during the boot sequence of a router, the router
copies the startup configuration file to the running configuration file (NVRAM to
RAM). Therefore, it is paramount that any time a change is made to a running
configuration, the change is also copied to the startup configuration.
Be sure to know the following main operating files and where they reside:
Operating File
Memory
Basic IOS
ROM
Boot Strap
ROM
Diagnostics
ROM
Current IOS
FLASH
Startup configuration [*]
NVRAM
Running configuration
RAM
[*]
Also called backup configuration file
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Router Modes.
Accessing a router can be done through a console port, a modem connection, or
through one of the operational interfaces. Once accessed, a router can be placed
in one of five primary modes:
 User
 Privileged
 Setup
 Rxboot
 Global configuration
There are more than five operational modes. However, additional modes are
used for very specific functions and are invariably lumped together in a category
called "other." The CCNA exam will only cover the five primary modes.
Each of these modes provides access to specific memory areas and functions,
as described in the following sections.
User Mode
User mode provides a display-only environment. You can view limited
information about the router but you cannot change the configuration of the
router.
Privileged Mode
Privileged mode enables you to perform an extensive review of the router. This
mode supports testing commands, debugging commands, and commands to
manage the router configuration files.
Setup Mode
Setup mode is triggered on router startup when no configuration file resides in
nonvolatile random access memory (NVRAM). This mode executes an
interactive prompted dialog box to assist in creating an initial router configuration.
RXBOOT Mode
A router's maintenance mode is called RXBOOT mode or ROM monitor mode.
This mode facilitates recovery functions when the router password is lost or the
IOS file stored in Flash memory has been erased or is corrupt. Pressing the
Break key (from a console terminal directly connected to the router) within the
first 60 seconds of startup also allows you to place the router in this mode.
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Global Configuration Mode
You perform simple configuration tasks that permeate all aspects of the router in
global configuration mode. For example, router names, router passwords, and
router banners are all configured in this mode.
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Exam Prep Questions
1.
Which of the following router components contain versions of the
router's configuration file? (Choose the two best answers.)
A. Flash memory
B. NVRAM
C. RAM
D. ROM
A1:
The correct answers are B and C. NVRAM contains the backup
configuration file for the router, whereas RAM contains the router's
active configuration file. Flash memory and ROM do not contain a
configuration file; they contain the router's IOS image files. Therefore,
answers A and D are incorrect.
2.
Where does the running configuration file exist in a Cisco router?
A. NVRAM
B. ROM
C. RAM
D. Flash memory
A2:
The correct answer is C. The running configuration file exists in RAM.
This file is erased when a router is reloaded or its power is cycled.
Answer B cannot be correct because ROM is a read-only device, and
configuration files are constantly being updated. Answer A is incorrect
because NVRAM is used to maintain the startup configuration file, not
the running configuration file. Answer D is incorrect because Flash
memory stores a copy of the IOS software, not the running
configuration files.
3.
What mode is triggered when a router is powered up for the first time?
A. User Mode
B. Priority Mode
C. Startup Mode
D. Setup Mode
A3:
Answer D is correct. A router goes into setup mode when power is
applied for the first time. Once the administrator has entered the basic
configuration requirements, a running configuration file is generated,
which in turn provides the user mode and priority mode for additional
configuration. Therefore, answers A and B are incorrect. Startup Mode
sounds correct, but there is no startup mode in the five basic modes of
operation.
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4.
What are three possible ways to connect to a router?
A. Through a console port
B. Remotely via a modem
C. Through the maintenance interface
D. Through an active router interface
A4:
Answers A, B, and D are correct. You can connect locally through a
serial cable connected to the console port or Telnet through an active
interface from a terminal. Most routers also allow for a modem
connection when the network is down and you cannot physically go to
the router location. There is no maintenance interface on a router.
5.
Power is restored after a major power outage. Your router, however,
has lost all of the configuration updates you made over the past month.
What has most likely happened?
A. The battery powering NVRAM could not maintain memory for the
length of the power outage.
B. The running configuration file did not have sufficient time to back
itself up to NVRAM when the power failed.
C. Power fluctuations inherent in power outages probably purged the
flash memory.
D. You forgot to save your changes.
A5:
Answer D is correct. When you change a running configuration file, you
must also save the changes to the startup configuration file in NVRAM.
Otherwise, when power is restored, the startup configuration file will be
copied to RAM and your changes will be lost. The running configuration
file does not back itself up. Therefore, B is incorrect. Answer A is
incorrect because NVRAM does not use a backup battery. Flash
memory could be purged as a result of power fluctuations, but it is a
very remote possibility. If flash memory were purged, the router would
use the IOS version from ROM, which would be very noticeable.
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6.
What, if any, are the differences between the IOS stored in ROM and
the IOS stored in EEPROM?
A. They are both the same; the ROM version is a backup for the version
in EEPROM.
B. The EEPROM version is a full version of IOS. The ROM version
contains only the basics required for initial operation.
C. The EEPROM version contains all of the configuration changes input
by the administrator. The ROM version is a basic unmodified version of
IOS.
D. ROM contains the running version of IOS, EEPROM contains
downloaded updates for the IOS.
A6:
Answer B is correct. The EEPROM contains the most current full
version of IOS used for day-to-day operation. ROM contains a scaled
down version of the IOS, which will get the router running in the event
no other operating system is available. Answer A is incorrect because
the versions are very different. Answer C is incorrect because "flashing"
and then downloading another version of IOS is the only way to change
the IOS version in EEPROM. The administrator cannot make changes
to the IOS configuration in EEPROM. Lastly, answer D is incorrect
because the current or running version of IOS resides in EEPROM.
7.
Why do Cisco routers maintain a basic version of IOS in ROM?
A. ROM is easy to change and provides an ideal way of updating the
router software.
B. Storing IOS in ROM prevents the users from modifying or stealing
the non-compiled version of IOS.
C. ROM contains the core operating code for IOS. Without it, the router
could not function.
D. ROM does not require power to maintain data. Therefore, if all else
fails, the scaled down version of IOS stored in ROM is capable of
getting the router up and running with basic functionality.
A7:
Answer D is correct. A basic version of IOS is stored in ROM so that the
router will always be able to be started with basic functionality. Answer
A is not correct because downloading to an EEPROM is far easier than
distributing and installing ROM chips. Answer B is incorrect because the
code in ROM is compiled and theft and/or tampering is really not a
concern. Lastly, C is not correct because the EEPROM stores a
complete version of IOS. The ROM version is a scaled down backup.
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8.
After four hours of work, you finally have the new Cisco router running
perfectly. When you return from lunch your boss mentions he made a
few simple changes and now it does not work. What would be the best
way to rectify the situation?
A. Purge the memories and start over.
B. Flash the EEPROM, download a clean IOS, and rebuild the running
configuration file.
C. Walk your boss back through what he remembers of the changes
and try to undo each change.
D. Turn the router off and then turn it on again.
A8:
Answer D is correct. Your boss has changed the running configuration
file. Chances are very good he did not save the running configuration
file to the startup file in NVRAM. Therefore, turning the router off and
then on again will erase the running configuration file and replace it with
a copy of the startup file. So long as you saved your work (you did save
your work, didn't you?), the router should come back up and work just
like it did before lunch. Answer A is incorrect because if you purged the
memories, you would lose the startup file and any hope of recovering
your prior work. Answer B is incorrect because your boss's actions only
affected the running configuration file. He could not compromise the
operating system so nothing would be accomplished by reloading the
IOS. Answer C is incorrect because he would probably not remember
exactly what he did, and even if he did, cycling the power would be
much faster and easier.
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9.
With regard to the situation in question 8, you must have done one of
the following for the situation to develop as it did. What would that most
likely be?
A. Went to lunch and left the console running in user mode.
B. Left the console running in global mode when you went to lunch.
C. Left the console running in setup mode while you went to lunch.
D. Went to lunch and left the console running in privileged mode.
A9:
Answer D is correct. Question 8 states that the router was running
perfectly prior to going to lunch. The router needs a running
configuration file to operate. The presence of a running configuration file
indicates setup mode had completed and will not run again until both
the running configuration file and startup file are lost. Answer C is
therefore eliminated as an option. User mode is a display only mode, so
if the console was left in that mode, your boss could only view parts of
the configuration, not change it. Therefore, answer A is incorrect. Global
mode only provides access to non-critical parameters, not configuration
files so B could not be correct. That leaves A as the correct answer.
Only privileged mode provides access to the running configuration file.
You must have gone to lunch and left the console running in privileged
mode.
10.
Now that the router in question 8 is up and running again, your boss
confides that what he was really trying to do was name the router after
his wife. He is now too embarrassed to try it himself so he asks you to
rename the router. What mode must the router be in to change its
name?
A. Global mode
B. Privileged mode
C. Setup mode
D. RXBOOT mode
A10:
Answer A is correct. The name of a router is one of those global
parameter changes that really does not affect the configuration files.
Answer C is a possibility, but the router is already running, so you are
not going to have access to setup mode. Privileged mode, answer B, is
for access to the configuration files. Router name is really not a part of
the configuration. Lastly, RXBOOT mode is maintenance and recovery,
not setting global parameters.
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TIP:
The exam will ask about the five modes of operation and the settings
that can be accessed in each mode. Although the previous three
questions make it sound like there is an underlying logic behind these
terms, they are in reality arbitrary. For you to answer these questions
correctly on the test you are probably going to have to memorize the
modes and their subsets. We will be going into the modes and their
subsets in more detail in the configuration chapters that follow.
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Chapter 9.
Configuring a Cisco Switch
Terms you'll need to understand:




Virtual local area network (VLAN)
Trunking
Inter-switch link (ISL)
VLAN Trunking Protocol (VTP)
Techniques you'll need to master:





Configuring a Cisco Switch
Creating and configuring VLANs
Assigning a VLAN to switched ports
Establishing a trunk connection between switches
Understanding and enabling VTP
A skill that few people possess is the ability to correctly configure a Cisco switch.
As you already know, newer applications increase demand for a switched
network. In this chapter, we walk you through the process of configuring a switch.
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Switch Startup.
The startup process for a Cisco switch can be monitored in the following ways:
 Observing the light-emitting diodes (LEDs) on the switch chassis
 Examining the Cisco Internetwork Operating System (IOS) output by
connecting a terminal to the switch's console port
Cisco catalyst switches have several LEDs that give a convenient visual indicator
of the switch's operational status. These LEDs are green when the switch is
functioning properly and amber when there's any sort of problem.
The Catalyst 1900 series switch executes a power-on-self-test (POST) each time
the switch is powered on, which can be monitored by watching the LEDs on the
switch chassis. The typical sequence is as follows:
1. Initially, all LEDs are green.
2. Each LED is associated with a specific POST. Each LED turns off after its
task is complete or turns amber if there's a problem.
3. The system LED turns amber if any test fails.
4. When the POST is complete, the LEDs blink, then turn off.
In addition to monitoring LEDs, any errors encountered during startup can be
checked by attaching a terminal to the console port of the switch and observing
the text output. The initial output from a Catalyst 1900 switch with no errors looks
similar to the following:
Catalyst 1900 Management Console
Copyright (c) Cisco Systems, Inc.1993-1999
All rights reserved.
Standard Edition Software
Ethernet address: 00-E0-1E-7E-B4-40
PCA Number: 73-2239-01
PCA Serial Number: SAD01200001
Model Number: WS-C1924-A
System Serial Number: FAA01200001
--------------------------------User Interface Menu
[M] Menus
[K] Command Line
[I] IP Address
[P] Console Password
Enter Selection:
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Configuring the Switch.
There are three different options for configuring a new Catalyst 1900 switch:
 Menu-driven interface
 Command-line interface (CLI) (only available on Enterprise Edition IOS
software)
 Web-based interface
These configuration options may vary depending on which model of switch you
have and which version of software it is running. Using the menu-driven interface
may seem like the easiest and quickest way to get your switch running. It is
important, however, that you learn how to configure the switch through the CLI as
well.
TIP:
The CLI is the standard interface used to configure any Cisco device running the
IOS, Cisco's proprietary OS. In addition, Cisco simulates some commands
through the CLI in the certification exam so beware.
The Web-based interface is another easy visual way to monitor and configure the
switch. It is important to note, however, that before you can use the Web-based
interface, the switch must have a valid Internet Protocol (IP) address. For this
reason, you must first configure at least an IP address using one of the other two
configuration methods.
Default Configuration
Cisco switches come with a default configuration that is actually usable in many
cases without any additional customization. Table 1 shows the default
configuration settings of a Catalyst 1900 switch. For most situations, you will
want to configure at least some basic options on the switch, such as an IP
address, default gateway, and duplex options. An example of where you would
use the default configuration would be an environment where VLANs, port
filtering, and so on are not an issue and you merely want the functionality of a
switch, albeit an expensive one.
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Table 1. Catalyst 1900 Default Configuration
Option
IP Address
CDP
Switching mode
100BASE-T port
10BASE-T port
Spanning tree protocol
Console password
Default Value
0.0.0.0
Enabled
Fragment-free
Auto-negotiate duplex mode
Half duplex
Enabled
None
Using the Menu-Driven Interface
Using the menu-driven interface to configure a Catalyst 1900 switch is a simple
and straightforward process. You must first connect to the switch through the
console port using a PC with terminal emulation software or Telnet into the
switch. As soon as the switch starts up, a menu that you use to select the option
to configure appears. The initial management console logon screen looks like
this:
User Interface Menu
[M] Menus
[K] Command Line
[I] IP Address
[P] Console Password
Enter Selection:
You may want to give the switch a password by pressing P and following the
instructions about setting the console password. You can enter the IP
Configuration menu by pressing I. You will see this once you enter the IP
Configuration menu:
Catalyst 1900 - IP Configuration
Ethernet Address:00-E0-1E-7E-B4-40
----------Settings---------[I] IP address
0.0.0.0
[S] Subnet mask
0.0.0.0
[G] Default gateway
0.0.0.0
[B] Management Bridge Group1 (fixed)
[M] IP address of DNS server 1
0.0.0.0
[N] IP address of DNS server 2
0.0.0.0
[D] Domain name
[R] Use Routing Information Protocol Enabled
----------Actions---------[P] Ping
[C] Clear cached DNS entries
[X] Exit to previous menu
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Enter Selection:
You can access the Management Console Main Menu by pressing M, which
shows you the following:
Catalyst 1900 - Main Menu
[C] Console Settings
[S] System
[N] Network Management
[P] Port Configuration
[A] Port Addressing
[D] Port Statistics Detail
[M] Monitoring
[B] Bridge Group
[R] Multicast Registration
[F] Firmware
[I] RS-232 Interface
[U] Usage Summaries
[H] Help
[X] Exit Management Console
Enter Selection:
Almost every option that you may need to configure for a Catalyst switch has an
associated menu command.
Using the CLI
The Command Line Interface (CLI), while slightly more difficult to learn than the
menu-driven interface, is important to know because it is used for configuration
across the entire Cisco product line. The CLI is available on switches that are
running the Enterprise Edition of Cisco's IOS. From the initial management
console logon screen, press K to enter the CLI. You will get a prompt that looks
similar to the following:
1900>
Enter privileged mode by using the enable command. Then, enter configuration
mode by using the config terminal command.
1900>enable
Enter Password: <enable password>
1900#config terminal
1900(config)#
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Configuring TCP/IP Options
Giving the switch an IP address is one of the first things that should be done. The
command used to do so is ip address {ip address} {subnet mask}. The default
gateway should also be specified by using the ip default-gateway {ip address}
command. The following is an example:
ip address 192.168.1.10 255.255.255.0
ip default-gateway 192.168.1.1
You may also need to configure a domain name for the switch and tell it how to
resolve names by giving it a name-server address, as shown in the following:
ip domain-name cisco.com
ip name-server 192.168.1.20
Now, we can view the TCP/IP information by using the show ip command:
hostname# show ip
IP Address:192.168.1.10
Subnet Mask:255.255.255.0
Default Gateway:192.168.1.1
Management VLAN: 1
Domain name: cisco.com
Name server 1:192.168.1.20
Name server 2:198.92.30.32
HTTP server :Enabled
HTTP port : 80
RIP :Enabled
In the previous code, you will see various components of a TCP/IP configured
device with all the relevant information such as the address, subnet mask,
gateway, and also that there is a Web server configured for port 80.
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VLANs.
A VLAN is a group of switched ports that acts as a separate, isolated LAN. There
can be several VLANs defined on a single switch. A VLAN can also span multiple
switches. Workstations in separate VLANs will never encounter traffic or share
bandwidth from other VLANs unless the data is routed. In other words, a router
or switch with routing capabilities is required if devices on different VLANs need
to communicate. It should be noted that VLAN configuration is done through the
switch and its software.
Remember that one of the main benefits of switches is that they segment a
network into many collision domains. Each port represents a single collision
domain, and devices share bandwidth only with other devices on the same
switch port. Unless a switch is segmented into VLANs, however, all of the
devices on the switch are still in the same broadcast domain; that is, all
broadcasts (and multicasts) are sent to each port throughout the switching fabric.
VLANs introduce a way to limit the broadcast traffic in a switched network (a job
normally associated with routers). When you create a VLAN by defining which
ports belong to it, you are really just creating a boundary for broadcast traffic.
This has the effect of creating multiple, isolated LANs on a single switch.
Figure 1 shows a 12-port switch that has been divided into two VLANs. Ports 1
through 6 are VLAN 1, and ports 7 through 12 are VLAN 2.
Figure 1. Simple VLAN.
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TIP:
It is important to understand the need for routers in a switched network. If
devices on different VLANs need to communicate, routing is required to facilitate
this exchange of data. Many of today's network systems are a collection of
routers and switches.
What happens when a device on one VLAN needs to communicate with a device
on another VLAN? Because a VLAN is a closed Layer 2 network, traffic must
cross a Layer 3 device to communicate with other VLANs. This means that a
router is required to facilitate the exchange of packets between VLANs.
The behavior we're describing here is that of Layer 2 switching. There are Layer
3 switches on the market that perform routing, but these are beyond the scope of
this E-Book.
It is possible for a device to participate in more than one VLAN by using a special
type of network card that performs ISL (Inter-switch link). ISL is discussed further
in the "ISL" section in this chapter.
The real benefit to using VLANs is that they can span multiple switches. Figure 2
shows two switches that are configured to share VLAN information.
Figure 2. VLANs spanning multiple switches.
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A large campus network may have hundreds of switches spread throughout
several buildings. A user can be put on the appropriate VLAN easily, no matter
where he or she is physically located. Users on the same VLAN do not have to
be connected to the same device. Therefore, LANs are no longer tied to the
physical location of users, but can be assigned based on department, functional
area, or security level. By isolating users according to department or functional
area, network administrators can keep the majority of data traffic within one
VLAN, thereby maximizing the amount of traffic switched at hardware speeds
versus what is routed at slower software speeds.
The ability to assign a user to a VLAN on a port-by-port basis makes adding,
moving, or deleting users simple. For example, let's say a user changes from the
accounting to the marketing department. If the network administrator designed
the network and VLANs by functional department, this user would have changed
VLANs. To accommodate this change, the administrator only has to make a
software configuration change in the switch by assigning that user's port to the
new VLAN.
In addition, VLANs provide the flexibility necessary to group users by security
level. This can greatly simplify applying a security policy to a network. In
summary, the benefits of VLANs are that they:
 Simplify security administration.
 Allow users to be grouped by functional area versus physical location.
 Simplify moving and adding users.
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Frame Tagging.
Frame Tagging is the method used by Cisco Catalyst switches to identify to
which VLAN a frame belongs. As a frame enters the switch, the switch
encapsulates the frame with a header that "tags" the frame with a VLAN ID. Any
time a frame needs to leave one switch for another, the tagged frame is sent
throughout the switching fabric. When the frame arrives at the destination switch,
the tag tells the switch to which VLAN the frame belongs. This process is
illustrated in Figure 3 using the VLAN IDs 10, 20, and 30. The tag is stripped off
of the frame before the frame is sent out to the destination device. This process
gives the illusion that all ports are physically connected to the same switch.
Figure 3. ISL and frame tagging.
TIP:
Be sure to understand the function of frame tagging, which "tags" a frame with a
user-defined VLAN ID.
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Trunk Connections.
Under normal circumstances, a switch port can carry traffic for a single VLAN
only. For VLANs to span multiple switches, a trunk connection must be created.
This trunk connection transports data from multiple VLANs. Trunk connections
allow VLANs to be used throughout the switching fabric of large networks.
Any FastEthernet or asynchronous transfer mode (ATM) port on a Catalyst
switch can be designated as a trunk port. This port typically connects to another
switch via a crossover 100BASE-T cable in the case of a Fast Ethernet trunk.
For the trunked port to transport multiple VLANs, it must understand frame tags.
ISL
ISL (Inter-switch link) is a technology developed by Cisco that allows a single
Ethernet interface to participate in multiple VLANs. When a trunk connection is
made on a Catalyst switch's Ethernet port, it utilizes ISL. ISL is also available on
Ethernet cards that can be used in servers or routers.
A device utilizing an ISL Ethernet card will appear to have many physical cards,
each connected to a different segment. ISL allows this single Ethernet card to
have many logical (virtual) addresses. The user must configure each logical
interface with an address that reflects the VLAN to which it belongs.
ISL works by allowing the frame-tagging information to be passed along to the
Ethernet card. The Ethernet card then reads the frame tag, which identifies the
VLAN to which the frame belongs. Conversely, the ISL Ethernet card creates the
frame tags when transmitting frames.
ISL is a technology proprietary to Cisco and, therefore, is not supported on
equipment made by other vendors. However, in mid-1998, the Institute of
Electrical and Electronics Engineers (IEEE) standardized a frame-tagging
process similar to Cisco's ISL. The new standard is a protocol called 802.1Q.
With 802.1Q, switches from multiple vendors can coexist in the same switching
fabric.
VTP
VTP (VLAN Trunking Protocol) is a protocol used between switches to simplify
the management of VLANs. Configuration changes that are made to a VTP
server are propagated across trunks to all connected switches.
All switches that are to be managed in this way must be members of the same
management domain. A VTP management domain is the entire group of
switches that share configuration information.
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For example, when you add a new VLAN to a member switch, the VLAN is
available in all of the network switches automatically. VTP allows switched
networks to scale to larger environments; otherwise, VLAN configuration would
have to be maintained manually on individual switches.
By default, Catalyst switches are set to a no-management-domain state. The
switches remain in a no-management state until a user configures the
management domain or they receive an advertisement for a domain over a trunk
link. The default VTP configuration parameters are shown in Table 2.
Table 2. Default VTP Configuration
Option
VTP Domain Name
VTP Mode
VTP Password
VTP Pruning
VTP Trap
Default Value
None
Server
None
Disabled
Enabled
VTP Modes.
When it has a management domain, a switch operates in one of three VTP
modes: server, client, or transparent. The default mode is server.
In VTP server mode, a switch can create, modify, or delete VLAN and other
configuration parameters for the entire VTP domain. VTP messages are sent
over all trunk links, and configuration changes are propagated to all switches in
the management domain.
In VTP client mode, the switch receives VTP messages and applies configuration
changes made from any VTP server. However, a client cannot create, change, or
delete VLAN information.
In VTP transparent mode, the switch forwards all VTP messages to other
switches in the domain, but does not use the configuration from VTP
advertisements. A VTP transparent switch can create, modify, or delete VLANs,
but the changes apply only locally and are not transmitted to other switches.
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VTP Pruning
VTP can detect if a trunk connection is carrying unnecessary traffic. By default,
all trunk connections carry traffic from all VLANs in the management domain. In
many cases, however, a switch does not need a local port configured for each
VLAN. In this event, it is not necessary to flood traffic from VLANs other than the
ones supported by that switch. VTP pruning enables the switching fabric to
prevent flooding traffic on trunk ports that do not need it. This is illustrated in
Figure 4.
Figure 4. VTP pruning.
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Configuring VLANs.
There are three methods that can be used to assign a switch port to a particular
VLAN. They are port-centric, static, and dynamic. In a port-centric configuration,
all nodes that are connected to ports within the same VLAN are given the same
VLAN ID. In this type of configuration, the network administrator's job is much
easier because of the ease of administering the VLAN.
In a static VLAN configuration the ports on a switch are hard coded and remain in
effect until the administrator changes them. This type of configuration is typical of
a network that is very well monitored, where changes are unlikely.
The third type of port configuration is dynamic. This type of configuration involves
more overhead on setup for the administrator because of the database
configuration. The ports on these switches automatically determine their
assigned VLAN. The VLAN assignment is determined by the type of protocol
(within a packet), MAC address, and logical addressing. A major benefit of this
type of configuration is that the administrator will notice any unauthorized or new
user is on the network. If a workstation happens to be connected to a port which
is unassigned, the switch will record the MAC address of the computer and check
its database to determine which VLAN to assign the workstation to.
In the rest of this chapter, we look at the Cisco commands used to configure,
monitor, and maintain VLANs and trunk connections.
Before you begin creating VLANs, you must determine whether the switch will
participate in a VTP domain that will synchronize VLAN configuration with the
rest of the network. Also, if you want to use VLANs across multiple switches, a
trunk connection must be made to interconnect the switches.
The steps required to configure VLANs are as follows:
1. Enable VTP (optional).
2. Enable trunking (optional).
3. Create VLANs.
4. Assign VLANs to ports.
Enabling VTP
When adding a new switch to an existing domain, it is good practice to add it in
VTP client mode initially. This way, you can prevent the switch from propagating
incorrect VLAN information to other switches. In the following example, however,
we are setting up a new VTP domain and will place the switch into server mode.
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The commands to do so are as follows:
1900#conf terminal
Enter configuration commands, one per line. End with CNTL/Z
1900(config)#vtp server
1900(config)#vtp domain ccnalab
To verify VTP information, use the show vtp command from EXEC privileged
mode:
hostname# show vtp
VTP version: 1
Configuration revision: 3
Maximum VLANs supported locally: 1005
Number of existing VLANs: 5
VTP domain name : ccnalab
VTP password
: vtp_server
VTP operating mode : Server
VTP pruning mode : Enabled
VTP traps generation : Enabled
Configuration last modified by: 0.0.0.0 at 00-00-0000 00:00:00
Enabling Trunking
The next step is to create a trunk connection to other switches that will be
sharing VLAN information. In the following example, assume that we are
connecting two Catalyst 1900 switches via their 100BASE-T ports using a
crossover category 5 Ethernet cable. We are using the FastEthernet ports known
in the IOS as f0/26.
The TRunk command has five options: on, off, desirable, auto, and nonnegotiate. Table 3 shows the function of each trunk mode.
Table 3. Trunk Command Options
Option
On
Off
Desirable
Auto
NonNegotiate
Function
Port goes into permanent ISL trunk mode. Negotiates with the
connected device to convert the link to a trunk.
Disables trunking on this port. Negotiates with the connected
device to convert the link to non-trunk.
Port will enter trunk mode if the connected device is set to on,
desirable, or auto; otherwise, port is a non-trunk.
Port will enter trunk mode if the connected device is set to on or
desirable; otherwise, port is a non-trunk.
Port goes into permanent ISL trunk mode, but no negotiation takes
place with the connected device.
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To enable trunking on a port, enter interface configuration mode for the desired
port first, and then use the trunk command with the appropriate option, as shown
here:
1900#conf terminal
Enter configuration commands, one per line. End with CNTL/Z
1900(config)#interface f0/26
1900(config-if)#trunk on
The same configuration must be executed for the appropriate port on the
connected device. Because we set the trunk to on mode in the previous example,
the corresponding port must be set to on, auto, or desirable for the trunk
connection to be established.
To verify the trunk operation, use the show trunk command. Its syntax is as
follows:
show trunk [a | b]
A Catalyst 1900 switch has two FastEthernet ports that can act as trunk
connections. They are known as interfaces f0/26 and f0/27. When using the
show trunk command, option A refers to the first trunk port (in this case, f0/26).
Option B is for port f0/27. So, to see the trunking status for FastEthernet port A
(f0/26), use the following command:
1900#show trunk a
DISL state: On, Trunking: On, Encapsulation type: ISL
Creating VLANs.
To create a new VLAN, use the vlan command from global configuration mode.
This command has several options that can be specified, but for our purposes, all
we need to have is a four-digit number to identify the VLAN and a name for it.
Each VLAN must have a unique numeric ID, which can be any number from 1 to
1005.
We will create a VLAN called Engineering and make it VLAN 2:
hostname(config)# vlan 2 name Engineering
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To verify the configuration of the VLAN, use the show vlan vlan# command:
1900#show vlan 2
VLAN Name
Status Ports
-------------- ----2 Engineering Enabled
------------- ------VLAN Type SAID MTU Parent RingNo BridgeNo Stp Trans1 Trans2
--------- ---- --- ------ ------ -------- --- ------ -----2 Ethernet 100009 1500
0
1
1
Unkn
0
0
Assigning VLAN to Ports
Now that the VLAN has been created, you can statically assign which ports will
be members of the VLAN. A port can belong to only one VLAN at a time. By
default, all ports are members of VLAN 1.
To assign a VLAN to a port, enter interface configuration mode for the
appropriate port, then use the vlan-membership command:
1900#conf terminal
Enter configuration commands, one per line. End with CNTL/Z
1900(config)#interface ethernet 0/8
1900(config-if)#vlan-membership static 2
To verify VLAN membership and to see which ports belong to what VLAN, use
the show vlan-membership command:
hostname# show vlan-membership
Port VLAN Membership Type Port
VLAN Membership Type
---- ------------------ ---- ---- --------------1
1
Static
14
2
Static
2
1
Static
15
2
Static
3
1
Static
16
2
Static
4
1
Static
17
2
Static
5
1
Static
18
2
Static
6
1
Static
19
2
Static
7
1
Dynamic
20
2
Static
8
1
Dynamic
21
2
Static
9
1
Dynamic
22
2
Static
10
1
Dynamic
23
2
Static
11
1
Dynamic
24
2
Static
12
1
Dynamic
AUI 2
Static
13
1
Dynamic
A
1
Static
B
2
Static
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Using the Web Interface
Catalyst 1900 and 2820 switches come with a built-in Web server that can be
used for monitoring and configuring the switch. It is very visually oriented and
allows you to change configuration options in a point-and-click environment. All
you have to know is the IP address of the switch, and you can point your Web
browser to the switch's IP address. If the switch has been configured with a
password, you will have to enter it to use the Web interface.
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Exam Prep Questions
1.
What must be done to allow a VLAN to span two or more switches?
A. Set up a VTP domain
B. Set up a trunk connection
C. Configure the duplex setting on the ports
D. Configure port security on the switch
A1:
Answer B is correct. A trunk connection must be established in order for
a VLAN to span multiple switches. Trunk ports recognize frame tags
and are therefore able to carry information on multiple VLANs. Answer
A is incorrect because a VTP domain is not necessary for switches to
share VLAN information. Answer C is incorrect because the duplex
setting does not have to be configured manually to connect two
switches. Answer D is incorrect because port security is not necessary
for a VLAN to span switches.
2.
What is ISL used for?
A. To allow an Ethernet interface to understand frame tags
B. To make two Ethernet interfaces appear as one
C. To connect an Ethernet switch with a high-speed core switch such as
ATM
D. To allow simultaneous routing and switching
A2:
The correct answer is A. ISL allows an Ethernet interface to understand
frame tags, which identify the VLAN to which a packet belongs. For this
reason, an ISL interface can participate in multiple VLANs, which is
necessary for a trunk connection. Answer B is incorrect because ISL
can actually have the opposite effect of this—a single Ethernet interface
may appear to be several by having multiple Layer 3 addresses.
Answers C and D are incorrect because these are not functions of ISL.
3.
What is the purpose of VTP pruning?
A. To detect loops in the switching fabric
B. To disable a trunk connection that creates a bridging loop
C. To simplify the management of VLANs
D. To prevent flooding unnecessary traffic across trunk connections
A3:
The correct answer is D. VTP pruning is used to prevent flooding of
unnecessary traffic across trunk connections. Answer A is incorrect
because this is a function of the spanning tree protocol. Answer B is
incorrect because this is not the purpose of VTP pruning. Answer C is
incorrect because this is the purpose of the VTP, not VTP pruning.
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4.
Which of the following is a valid command to create a VLAN on a
Catalyst 1900 switch and name it Accounting?
A. switch(config)#create vlan 10 name Accounting
B. switch#create vlan 10 name Accounting
C. switch(config)#vlan 10 name Accounting
D. switch#vlan 10 name Accounting
A4:
The correct answer is C. The correct syntax to create a VLAN in
command mode is vlan {number}name {name} from global configuration
mode. Answers A and B are incorrect because the word "create" is not
a part of this command. Answer D has the correct syntax for the
command, however, the switch is not in configuration mode; therefore,
answer D is incorrect.
5.
Which of the following commands will assign Ethernet port 9 on a
Catalyst 1900 to VLAN 20?
A. interface Ethernet 0/9 and vlan-membership static 20
B. vlan-membership interface Ethernet 0/9 static 20
C. interface Ethernet 0/9 and vlan 20
D. vlan 20 interface Ethernet 0/9
A5:
The correct answer is A. To assign an interface to a VLAN, you must
first enter port configuration mode by using the interface Ethernet 0/9
command from global configuration mode. Then, use the vlanmembership command to assign a VLAN to the port. Answers B, C, and
D are all invalid syntax.
6.
Which VLAN port configuration option requires
administration because of database configuration?
A. Static
B. Port-centric
C. Dynamic
D. Dynamic-relational
A6:
The correct answer is C. The dynamic configuration requires more initial
overhead because the administrator has to configure the switches
database. Answer A is incorrect because static is also labor intensive
up front, but not as much as dynamic. Answer B is incorrect because
port-centric is the easiest of the three to administer. Answer D is
incorrect because there is no such thing as a dynamic-relational
configuration for Cisco's switch ports. The only configuration options are
static, port-centric, and dynamic.
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more
up-front
7.
Which VLAN port configuration option states that no other packets will
flow over into other workstation's domains?
A. Static
B. Port-centric
C. Dynamic
D. Static filtered
A7:
The correct answer is D. Port-centric is the correct choice because of
the ability to assign VLAN IDs to ports in the same VLAN. Answer A,
static, and B, dynamic, are incorrect because neither has the capability
of assigning IDs to specific ports within the same VLAN. Answer D is
incorrect because static filtered is not a VLAN port configuration option.
8.
Which of the following commands could be used to assign an IP
address to a Catalyst 1900 switch?
A. ip-address 10.1.1.10 255.0.0.0
B. ip address 10.1.1.10 and subnet-mask 255.0.0.0
C. ip 10.1.1.10/255.0.0.0
D. ip address 10.1.1.10 255.0.0.0
A8:
The correct answer is D. The command for assigning an IP address to a
switch from the command prompt is ip address {address}{subnet-mask}.
Answers A and C are incorrect because these are invalid commands.
Answer B is incorrect because subnet-mask is not a valid command.
9.
What command can be used on a Catalyst 1900 switch to view it's
TCP/IP configuration information?
A. show tcp/ip
B. show ip
C. show network
D. display network
A9:
The correct answer is B. The show ip command will display information
about the TCP/IP settings the switch is using. Answers A, C, and D are
all invalid commands.
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10.
A marketing department has 15 stations on the fourth floor connected to
a Cisco 1900 switch. The department has an additional 12 stations on
the second floor connected to a second Cisco 1900 switch. The two
switches are connected via standard 100BASE-T ports using a
crossover cable. The department head has stated that she wants
everybody on the same department LAN. Which trunk command option
would you use for the port connected to the crossover cable on the fifth
floor to ensure communications between the two groups?
A. On
B. Off
C. Desirable
D. Auto
A10:
Answer B is correct. Trunking is used when VLANs span more than one
switch. In this case, the department head wants a single LAN so
trunking would not be needed or desired. Traffic will automatically flow
across the crossover cable as needed. Answer A is not correct because
it would force the port into permanent ISL trunk mode. Answer C is not
correct because if the port on the second floor were set to anything
other than "off", both ports would immediately go into trunk mode.
Answer D is not correct because if the port on the second floor was set
to "desirable" or "on", both ports would again go into trunk mode.
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Chapter 10.
Configuring a Cisco Router
Terms you'll need to understand:












Running and startup configuration files
TFTP (Trivial File Transfer Protocol)
Configuration register
Standard access Lists
enable secret password command
service password-encryption command
Boot field
Link Control Protocol (LCP)
Point-to-Point Protocol (PPP)
ISDN (Integrated Services Digital Network)
Frame relay
IP extended access lists
Techniques you'll need to master:
 Copying and moving configuration files
 Configuring a router during initial setup
 Identifying main Cisco IOS commands for router startup
 Loading and backing up of Cisco IOS
 Configuring a router to use PPP, ISDN, and/or frame relay
 Configuring routing protocols
 Configuring standard and extended access list for IP
If you ever wanted some hands-on experience to help you in your CCNA
preparation (of course you do), then this chapter is for you. This chapter focuses
on a number of very important and often-applied skills in networking. The ability
to manage configuration files, to load and copy Cisco software, and to
understand the impact of these types of commands is vital for your success.
More importantly, you need to master these crucial skills to avoid causing a
disaster in your company's network and pass the exam of course. Understanding
the many password types and security levels used on Cisco routers is equally
important. Finally, this chapter describes and illustrates the steps required to set
up a router via the initial setup sequence. However, let's start with a review of key
concepts from when we first introduced router configuration.
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Router Elements.
This section describes the various interface modes in which you can work on a
router. It also provides an overview of the different components within a router
and explains how to examine the status of each of those components.
Router Modes
Regardless of how you access a router (through the console port, a modem
connection, or a router interface), you can place it in one of several modes. Other
router modes exist beyond the user and privileged modes in previous chapters.
Each router mode enables specific functions to be performed. The different types
of router modes include user, privileged, setup, RXBOOT, global configuration,
and other configuration modes, as shown in Table 1.
Table 1. Router Modes
Mode
Function
User
Limited display
Privileged Display,
testing,
debugging,
configuration
file
manipulation
Setup
Create initial router
configuration
RXBOOT
Global
Others
How Accessed
Prompt
Log in to the router
Router>
From user mode, enter Router#
theenable command
During router startup, if
the configuration file is
(console dialog)
Perform
router Press the Break key
recovery
during router startup
(console access only)
Perform
simple From EXEC privileged
configuration
mode,
enter
the
configure command
Perform complex and From
within
global
multiline configuration configuration mode, the
command
entered
varies
Interactive dialog
missing
from
NVRAM prompts
>
Router (config)#
Router (config<mode>)#
User Mode
As stated earlier, user mode provides a display-only environment. You can view
limited information about the router but cannot change the configuration.
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Privileged Mode
Privileged mode enables you to perform an extensive review of the router. This
mode supports testing commands, debugging commands, and commands to
manage the router configuration files.
Setup Mode
Setup mode is triggered on router startup when no configuration file resides in
nonvolatile random access memory (NVRAM). This mode executes an
interactive prompted dialog box to assist in creating an initial router configuration.
RXBOOT Mode
A router's maintenance mode is called RXBOOT mode or ROM monitor mode.
This mode facilitates recovery functions when the router password is lost or the
IOS file stored in Flash memory has been erased or is corrupt. Pressing the
Break key (from a console terminal directly connected to the router) within the
first 60 seconds of startup also allows you to place the router in this mode.
Global Configuration Mode
You perform simple configuration tasks in global configuration mode. For
example, router names, router passwords, and router banners are configured in
this mode.
Other Configuration Modes
You perform complex router-configuration tasks in several other configuration
modes. You enter interface, subinterface, controller, and routing protocol
configurations from within these other modes. Table 2 provides a summary of the
syntax for each router mode.
Table 2. Router Configuration Summaries
Configuration Mode
Interface
Subinterface
Router
IPX-Router
Line
Controller
Map-List
Router-Map
Cisco CCNA (640-801).doc
Router Prompt
NFLD(config-if)#
NFLD(config-subif)#
NFLD(config-router)#
NFLD(config-ipx-router)#
NFLD(config-line)#
NFLD(config-controller)#
NFLD(config-map-list)#
NFLD(config-route-map)#
197
Router Components
Every router contains several components that compose its configuration. These
components are RAM, NVRAM, Flash memory, ROM, and interfaces.
RAM
RAM serves as a working storage area for the router and contains data such as
routing tables, various types of cache and buffers, and input and output queues.
RAM also provides storage for temporary memory for the router's active IOS and
configuration file (the running configuration file). However, all the contents of
RAM are lost if the router is powered down or restarted.
NVRAM
Unlike RAM, nonvolatile RAM (NVRAM) retains its contents when the router is
powered down or restarted. NVRAM stores permanent information, such as the
router's backup configuration file. The startup configuration file is retrieved from
NVRAM during startup and loaded into RAM.
Flash
Flash memory stores the Cisco IOS image and associated microcode. Flash
memory is erasable, electronically reprogrammable ROM that retains its contents
when the router is powered down. Several copies or versions of an IOS image
can be contained in Flash memory. Flash memory allows software to be
upgraded without chips on the processor being added, removed, or replaced.
ROM
Like Flash memory, ROM contains a version of IOS—usually an older version
with minimal functionality. It also stores the bootstrap program and power-on
diagnostic programs. However, software upgrades can be performed only by
replacing the ROM chip itself.
Interfaces
Interfaces provide the network connections where packets move in and out of the
router. Depending on the model of router, interfaces exist either on the
motherboard or on separate, modular interface cards.
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Router Status
Routine administration of a router involves examining the status of the router.
The show command enables you to view the status of the router's components.
You can execute show from either user or privileged mode. However, the
keywords used with the show command are different in the user and privileged
modes.
Figure 1 illustrates some of the more common show command keywords and the
router components with which they are associated
Figure 1. The show command's and associated router components.
The show version command displays hardware and software version numbers
relating to a specific router, as shown here:
NFLD#show version
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-IS-L), Version 11.3(7)T,
RELEASE SOFTWARE (fc1)
Copyright (c) 1986-1998 by Cisco Systems, Inc.
Compiled Tue 01-Dec-98 10:21 by ccai
Image text-base: 0x0303A9D8, data-base: 0x00001000
ROM: System Bootstrap, Version 11.0(10c)XB1, PLATFORM SPECIFIC
RELEASE SOFTWARE
(fc1)
Cisco CCNA (640-801).doc
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BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R),
Version 11.0(10c)XB1, PLATFORM
SPECIFIC RELEASE SOFTWARE (fc1)
NFLD uptime is 2 days, 7 hours, 17 minutes
System restarted by reload
System image file is "flash:c2500-is-l_113-7_T",
booted via flash
cisco 2500 (68030) processor (revision M) with
6144K/2048K bytes of memory.
Processor board ID 06972781, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
1 Ethernet/IEEE 802.3 interface(s)
1 Token Ring/IEEE 802.5 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2102
NFLD#
The show memory command displays statistics about the router's memory, as
shown here:
NFLD#show memory
Head Total(b) Used(b)
Processor 87510 5733104 809476
I/O 600000 2097152 488444
Free(b) Lowest(b) Largest(b)
4923628
4872780
4890708
1608708
1476032
1532904
Processor memory
Address
87510
87968
884C8
89420
89C1C
89E48
8AA2C
8AA84
8AEDC
8AF60
8AFE4
8B068
8B0EC
8B520
8B934
Bytes Prev. Next Ref PrevF NextF Alloc PC What
1068 0
87968 1
31A0B86 List Elements
2868 87510 884C8 1
31A0B86 List Headers
3884 87968 89420 1
314B0E0 TTY data
2000 884C8 89C1C 1
314D52E TTY Input Buf
510 89420 89E48 1
314D55E TTY Output Buf
3000 89C1C 8AA2C 1
31B31BA Interrupt Stack
44 89E48 8AA84 1
36C16D8 *Init*
1068 8AA2C 8AEDC 1
31A0B86 messages
88 8AA84 8AF60 1
31AFBAC Watched Boolean
88 8AEDC 8AFE4 1
31AFBAC Watched Boolean
88 8AF60 8B068 1
31AFBAC Watched Boolean
88 8AFE4 8B0EC 1
31AFBAC Watched Boolean
1032 8B068 8B520 1
31B796A Process Array
1000 8B0EC 8B934 1
31B7D1C Process Stack
480 8B520 8BB40 1
31B7D2E Process
Cisco CCNA (640-801).doc
200
8BB40
108 8B934 8BBEC
8BBEC
44 8BB40 8BC44
8BC44
1068 8BBEC 8C09C
--More--
1
1
1
31AFDBC Process Events
36C16D8 *Init*
31A0B86 List Elements
The show protocols command displays the Network layer protocols and
addresses that are configured on the router, as shown here:
NFLD#show protocols
Global values:
Internet Protocol routing is enabled
Ethernet0 is up, line protocol is up
Internet address is 172.16.57.1/24
Serial0 is administratively down, line protocol is down
Serial1 is administratively down, line protocol is down
TokenRing0 is administratively down, line protocol is down
NFLD#
The show running-config command displays the active configuration file. Use the
write terminal command if the router's IOS version is 10.3 or earlier. The write
terminal command is also supported in later versions of the IOS:
NFLD#show running-config
Building configuration...
Current configuration:
!
version 11.3
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname NFLD
!
interface Ethernet0
description Engineering LAN Segment
ip address 172.16.57.1 255.255.255.0
!
interface Serial0
no ip address
no ip mroute-cache
shutdown
no fair-queue
!
interface Serial1
no ip address
shutdown
!
interface TokenRing0
no ip address
shutdown
!
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ip classless
!
!
line con 0
line aux 0
line vty 0 4
login
!
end
NFLD#
The show startup-config command displays the backup configuration file. Use the
show configuration command if the router's IOS version is 10.3 or earlier. The
show configuration command is also supported in later versions of the IOS:
NFLD#show startup-config
Using 424 out of 32762 bytes
!
version 11.3
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname NFLD
!
interface Ethernet0
description Engineering LAN Segment
ip address 172.16.57.1 255.255.255.0
!
interface Serial0
no ip address
no ip mroute-cache
shutdown
no fair-queue
!
interface Serial1
no ip address
shutdown
!
interface TokenRing0
no ip address
shutdown
!
ip classless
!
!
line con 0
line aux 0
line vty 0 4
login
Cisco CCNA (640-801).doc
202
!
end
NFLD#
The show interface command displays statistics for all the interfaces on the
router or a specific interface, if one is defined:
NFLD#show interface ethernet 0
Ethernet0 is up, line protocol is up
Hardware is Lance, address is 00e0.1e60.9d9f
(bia 00e0.1e60.9d9f)
Description: Engineering LAN Segment
Internet address is 172.16.57.1/24
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set, keepalive set (10 sec)
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output 00:00:03, output hang never
Last clearing of "show interface" counters never
Queueing strategy: fifo
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
42 packets input, 9697 bytes, 0 no buffer
Received 42 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 input packets with dribble condition detected
80 packets output, 16167 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out
NFLD#
The show flash command displays information about the Flash memory device,
as shown here:
NFLD#show flash
System flash directory:
File Length Name/status
1 7181580 c2500-is-l_113-7_T
[7181644 bytes used, 1006964 available, 8388608 total]
8192K bytes of processor board System flash (Read ONLY)
NFLD#
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Managing Configuration Files.
The process of managing configuration files is straightforward; however, it is
increasingly difficult because of the different versions of Cisco software and the
wide variety of architectures used in Cisco hardware. This section will bring light
to these subjects; present an overview of the different types of configuration files
and the commands used to move, display, and copy these files; and, finally,
highlight some of the areas that can cause confusion when managing
configuration files.
Types of Configuration Files
Cisco IOS software uses and requires a configuration file to determine how a
router is to function. Typically, network administrators enter the commands
necessary for their environment into a router configuration file. Only two types of
configuration files exist for the context of the CCNA exam:
 The running configuration file exists in RAM and contains the commands
that Cisco IOS uses to drive the actions of the router.
RAM is erased during power cycles or software reloads. Therefore, the
running configuration file is erased as well. Startup configuration files,
which provide a backup for the running configuration files, reside in
NVRAM and are not erased with a power down.
 The startup configuration file exists in NVRAM and is the backup for the
running configuration file.
The router will always use the running configuration file to execute. However, any
time a router is restarted (cycling power or reloading the software), the running
configuration file is erased and the startup configuration file is the only remaining
configuration file. During the boot sequence of a router, the router copies the
startup configuration file to the running configuration file (NVRAM to RAM).
Therefore, it is paramount that any time a change is made to a running
configuration, the change is also copied to the startup configuration. The many
ways of preventing the loss of changes made are discussed in this chapter.
Displaying the Running and Startup Configuration Files.
The purpose of displaying a running or startup configuration file is to determine
the configuration commands being executed on a router. Use the show runningconfig and show startup-config commands to show the running configuration and
startup configuration files, respectively. Displaying the running configuration file
shows the commands being executed at the time that the show command is
executed, as shown here:
Router#show running-config
Building configuration...
Current configuration:
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204
Last configuration change at 03:25:38 UTC Sat Jan 1 2000
version 11.2
no service password-encryption
no service udp-small-servers
no service tcp-small-servers
hostname Router
enable secret 5 $1$2uUP$2I.L0xxD3wnX.7WDMHzb60
enable password cisco
no ip domain-lookup
interface Serial0
ip address 138.144.2.2 255.255.255.0
encapsulation frame-relay
bandwidth 2000
frame-relay lmi-type cisco
interface Serial1
no ip address
shutdown
!
interface TokenRing0
ip address 138.144.3.1 255.255.255.0
ring-speed 16
!
interface TokenRing1
ip address 138.144.4.1 255.255.255.0
ring-speed 16
!
router igrp 1
network 138.144.0.0
!
no ip classless
!
snmp-server community public RO
!
line con 0
line aux 0
line vty 0 4
password cisco
login
!
end
The Router# prompt indicates that the command is initiated from the EXEC
privileged (enable) command line. It is important to know in what mode a
command should be executed
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Configuring the Running and Startup Configuration Files
The running configuration file often requires changes while the router is
functioning. Cisco IOS is designed to accept changes to a running or startup
configuration file without restarting (reloading) or cycling the power of the router.
The following commands are used to manipulate the configuration files:
 Router# configure terminal— Allows a user to add, change, or delete
commands in the running configuration file while the router is executing.
 Router# configure memory— Allows a user to add, change, or delete
commands in the startup configuration file.
Making changes to the running configuration file will immediately affect the
behavior of a router.
Backing Up and Restoring Configuration Files
Configuration files are copied and moved constantly in most networks. One
common method of copying files is with the use of a Trivial File Transfer Protocol
(TFTP) server. Most Unix machines have built-in TFTP support. Also, TFTP
server programs are available for Windows-based PCs. Cisco makes a TFTP
server program that is available to registered users on its Web site at the
following Web address: www.cisco.com/pcgi-bin/tablebuild.pl/tftp. Cisco routers
use a TFTP server to load IOS and to copy software and configuration files. To
copy a file using TFTP, one device needs to be executing TFTP server software
and the other device needs to be executing the client software. Cisco routers are
equipped with both functions. Network administrators often need to back up a
running or startup configuration file on a central server. The following command
sequence accomplishes this goal:
Router# copy running-config TFTP
Remote host []? 172.15.10.2 (IP Address of TFTP Server)
Name of configuration file to write [router-confg]? <Return>
Write file Router-confg on host 172.15.10.2? [confirm] <Return>
Building configuration...
Writing Router-confg !!!!!!!!!!!!!!!!![OK]
TIP:
Pay attention to the order and syntax of commands during the test. The function
of a command can completely change, depending on the syntax. Also be aware
that Cisco networking devices accept the short form of commands, for example
config t instead of configure terminal. We use the long forms exclusively in this
book because they are easier to remember.
The reverse process occurs when a configuration file is copied from a central
server to an executing router. This process is most often used when a router has
gone dead or someone has accidentally deleted the configuration file on the
router. If the running configuration was backed up on a TFTP server, it is really
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206
simple to restore the configuration file. The first step for restoring the
configuration file on a router is to determine Internet Protocol (IP) connectivity
from the central server to the router. This might require the use of a ping test
and/or the configuration of an IP address on the router. The following command
sequence is used for restoring a running configuration file:
Router# copy TFTP running-config
Host or network configuration file [host]? <Return>
Address of remote host [255.255.255.255]? 172.15.10.2 (TFTP
Server)
Name of configuration file [Router-confg]?Router-confg (File name)
Configure using Router-confg from 172.15.10.2? [confirm] <Return>
Loading Router-confg from 172.15.10.2 (via serial 1): !!!!!
[OK - 875/32723]
Router#
Exercise caution when performing configuration file changes across networks,
especially to remote sites. Visit the Cisco Web site (www.cisco.com) and utilize
the search engine to identify anything you might need to be aware of while
performing configuration file backups or restores in your network. Always be sure
to find hardware-specific features before changing configuration files or Cisco
IOS software.
Another method of backing up a running configuration is to save it to NVRAM.
You should complete this process after every change to the running configuration
file, unless a good reason exists to keep the startup configuration different. By
copying the running configuration to NVRAM, you are ensuring that if the router
is reloaded or the power is cycled, it will boot with the same configuration you are
currently executing. The following command sequence is required for this
process:
Router#copy running-config startup-config
Building configuration...
[OK]
The startup configuration file can also be copied into RAM, thereby overwriting
the running configuration file, by performing the following command:
Router# Copy startup-config running-config
TIP:
It is necessary to know all the backup and restore commands for the CCNA
exam. Be sure to pay special attention to the syntax of these commands. It is
easy to forget the sequence of words for the different commands.
Finally, the startup configuration file can be completely erased. When this occurs,
the router boots into setup mode the next time it is reloaded:
Router#erase startup-config
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207
Router Passwords
The router passwords on the Cisco router provide security against unwanted
users; Cisco IOS passwords were never intended to resist a determined,
intelligent attack. Many programs exist (Cisco is aware of these programs) that
can crack the MD5 encryption algorithm Cisco IOS employs. Cisco always
recommends that some type of user-authentication protocol be used to enhance
the security of Cisco routers. RADIUS and TACACS are two of the more popular
authentication methods that major corporations use today. Cisco routers utilize
five different password types to provide security.
The enable password and enable secret Password Commands
The enable password and enable secret password commands are designed to
provide an additional layer of security for passwords. Both commands allow you
to establish an encrypted password that requires users to enter access enable
mode. The enable secret command was developed to use an improved
encryption algorithm. The enable secret password overrides the password for
enable password when it is present. An enable secret password can be entered
by issuing the following command:
Router(config)#enable secret NFLD
Router#
The enable password and enable secret commands also provide for security
levels. These options are not part of the objectives set by the CCNA exam and
are not, therefore, presented in this E-Book.
The console and auxiliary Password Commands.
The console and auxiliary password commands restrict user mode access via the
console or auxiliary ports on the router:
Router(config)#line aux 0
Router(config-line)#login
Router(config-line)#password NFLD
The login command designates that you want users to have to enter their
passwords every time they connect to the router via the auxiliary port. The login
command can be added to the console port to require a password login as well.
The console password is set with the same command format as the aux
password, except that the keyword aux is changed to con.
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208
The virtual terminal Password Command
The virtual terminal (or vty) password restricts user modes accessed via a Telnet
session. The virtual terminal password must be set; otherwise, a user will not be
able to log in to the router with a Telnet session. Multiple virtual terminal sessions
can be engaged at one time. A separate password can also be specified for each
virtual terminal session, as shown in the following:
Router(config-line)#line vty 0 4
Router(config-line)#login
Router(config-line)#password NFLD
The Cisco IOS allows five simultaneous Telnet connections. Notice that the
syntax is line then line type and line number. Cisco interface numbers always
start with 0. For this example, we are specifying all five ports, numbers 0 through
4, to designate five virtual terminals that all use the password "NFLD."
Of the five different types of passwords, only the enable secret password is
encrypted by default. For the remaining passwords, you must use the service
password-encryption command. This command encrypts the enable, console,
auxiliary, and virtual terminal passwords:
Router(config)#service password-encryption
Passwords that have already been set in the configuration file will not become
encrypted; only passwords that are entered after the service passwordencryption command has been entered will be encrypted. The service passwordencryption command does not provide a high level of network security, but it
helps to keep unauthorized individuals from viewing a password in a
configuration file.
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Router Identification and Banner.
A router's name is referred to as the hostname. The default hostname for all
Cisco routers is "Router." You can change the hostname of a router in global
configuration mode by entering the hostname command. The hostname is
changed with the following commands:
Router(config)#hostname NFLD
NFLD(config)#
Notice that the hostname changed from "Router" to "NFLD" immediately after
executing the command.
The banner motd command allows you to display a message-of-the-day (MOTD)
banner every time you log in to the router. Even though the banner message was
designed to convey day-to-day messages, it is typically used for displaying
security messages for legal reasons:
NFLD(config)#banner motd * Authorized Access Only,
All Violations Will Be Prosecuted *
NFLD(config)#
The asterisk (*) before the word "Authorized" and after the word "Prosecuted"
represents the start and finish of the text to be displayed as the banner.
In this scenario, the next time you Telnet into the router, the MOTD banner will
display the following message:
Authorized Access Only, All Violations Will Be Prosecuted.
User Access Verification
Password:
A description can be added to every interface using the description command.
Typically, an interface description, which is limited to 80 characters, is used to
describe the function of the interface, as shown in the following:
NFLD(config)#interface s0
NFLD(config-line)#description 56K between NFLD and San Diego
NFLD(config-line)#
The next time someone views the running configuration file, she will see the
following description:
interface Serial0
description 56K connection between NFLD and San Diego
ip address 138.144.2.2 255.255.255.0
encapsulation frame-relay
bandwidth 2000
frame-relay lmi-type cisco
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210
Initial Configuration of a Cisco Router.
The first time a Cisco router is powered on, the startup configuration file is blank,
so it will boot into the initial configuration dialog. This dialog is designed to walk a
novice through the basic steps and requirements of configuring a Cisco router.
The initial configuration dialog is a menu-driven command-and-response query
designed to configure a router with a bare-bones configuration. The dialog will
start anytime a configuration file is not found in NVRAM during the boot
sequence, as described previously. The two instances in which a configuration
file will not exist in NVRAM are when the router is powered on for the first time
and when the router is reloaded subsequent to the startup configuration file being
erased.
The following code is a sample initial router configuration phase:
Would you like to enter the initial configuration
dialog? [yes] <Return>
First, would you like to see the current interface
summary? [yes] <Return>
Any interface listed with OK? Value "NO" does not have a
valid configuration
Interface
IP-Address
OK?
Method
Status
Protocol
Serial 0
unassigned
NO
not set
up
down
Serial 1
unassigned
NO
not set
up
down
Ethernet 1
unassigned
NO
not set
up
down
Ethernet 2
unassigned
NO
not set
up
down
Configuring global parameters:
TIP:
Notice that in the configuration dialog, many of the questions have answers in
brackets following them. These are the default values or answers for the
questions. To accept a default value, simply press Enter and move on to the next
question. If you don't want to use the default value, simply enter your own. Also,
if at any time you are stumped as to the proper syntax to use, you can always
type ? at the prompt for help or press the Tab key, which will finish your syntax
for you.
The preceding interface summary indicates that the router has two serial and two
Ethernet interfaces. In this example, we will configure both serial interfaces and
neither of the Ethernet interfaces. None of the four interfaces has been assigned
an IP address, which is indicated by the "unassigned" designation, listed under
the IP-Address column. The status of the interface is set to "up" because this is
the default value. We must manually shut down the interface to turn it off.
However, the protocol is listed as "down" because no active connections are on
the interface. After the interface summary is displayed, the next step in the initial
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configuration dialog is to configure the hostname, passwords, routing protocols,
and IP addressing, as shown here:
Enter host name [Router] NFLD
The enable secret is a one-way cryptographic secret used instead
of the enable password when it exists.
Enter enable secret: NFLD
The enable password is used when no enable secret exists and when
Using older software and some boot images.
Enter enable password: Cisco
Enter the virtual terminal password: Telnet
Configure SNMP Network Management? [yes]: no
Configure IP? [yes] <Return>
Configure IGRP Routing? [yes]: no
Configure RIP Routing? [yes]: no
Configure Interfaces:
Configuring interface Ethernet 0:
Is this interface in use? [yes] no
Configuring interface Ethernet 1:
Is this interface in use? [yes] no
Configuring interface Serial 0:
Is this interface in use? [yes] <Return>
Configure IP on this interface? [yes] <Return>
Configure IP unnumbered on this interface? [no] : <Return>
IP Address for this interface: 172.29.3.4
Number of bits in subnet field [8]: <Return>
Class B network is 172.29.0.0, 8 subnet bits; mask is
255.255.255.0
Configuring interface Serial 1:
Is this interface in use? [yes] <Return>
Configure IP on this interface? [yes] <Return>
Configure IP unnumbered on interface? [no] : <Return>
IP Address for this interface: 172.29.4.3
Number of bits in subnet field [8]: <Return>
Class B network is 172.29.0.0, 8 subnet bits; mask is
255.255.255.0
Now we have configured the two serial interfaces, set up our passwords, and
chosen any routing protocols we want to utilize. For the sake of simplicity,
however, we did not turn on either the Routing Information Protocol (RIP) or the
Interior Gateway Routing Protocol (IGRP). The router will then show us the
configuration that we created:
The following configuration command script was created:
Hostname NFLD
Enable secret 5 09371034073401823
Enable password Cisco
Line vty 0 4
Password Telnet
No snmp-server
!
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ip routing
!
interface Ethernet 0
Shutdown
No ip address
Interface Ethernet 1
Shutdown
No ip address
Interface Serial 0
Ip address 172.29.3.4 255.255.255.0
Interface Serial 1
Ip address 172.29.4.3 255.255.255.0
!
end
Use this configuration? [yes/no]: yes
We have now completed the initial configuration dialog and successfully
configured the NFLD router with IP addressing.
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PPP Overview.
Point-to-Point Protocol (PPP) encapsulates Network layer information for
transmission over point-to-point links. It was designed by developers on the
Internet and is described by a series of documents called Request for Comments
(RFCs)—namely, 1661, 1331, and 2153. Figure 2 shows how PPP's layered
architecture relates to the Open Systems Interconnection (OSI) model.
Figure 2. The OSI reference model and PPP.
PPP consists of two main components:
 Link Control Protocol (LCP)— Establishes, configures, and tests the
connection
 Network Control Program (NCP)— Configures many different Network
layer protocols
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Configuring PPP
Configuring PPP on a Cisco router requires that both global and interface
configuration commands be executed on both the local and remote routers.
Figure 3 presents an example of two routers that need to establish a PPP link.
Figure 3. Point-to-Point Protocol (PPP).
A username and password must be set, so the following global configuration
command must be executed:
Username name password secret-password
In this command, name and secret-password indicate the name of the remote
host and the password to use for authentication. The password must be the
same on both the local and remote routers. Table 3 lists the interface commands
that must be executed to configure PPP. Figure 4 presents the global and
interface configuration commands for router A and router B.
Figure 4. PPP configuration.
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Monitoring PPP.
You can monitor PPP activity with the show interface and debug ppp chap
commands. The show interface command enables you to view PPP, LCP, and
NCP information. The following output shows an example of PPP activity on an
interface:
TIP:
Notice that the "show interface" in the following example is abbreviated to "sh
int". Almost all Cisco commands can be abbreviated. However, we recommend
you use the full command until you are comfortable with all aspects of
configuration. The abbreviations are hard to remember at first, but fairly easy to
recognize once written. You will not be asked to provide any abbreviation on the
test and you will probably not see any. However, we want to make sure you know
they exist and will include some as we go along so you can see what they are
like.
RouterA#sh int s0
Serial0 is up, line protocol is up
Hardware is HD64570
Internet address is 172.16.1.1/16
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
rely 255/255, load 1/255
Encapsulation PPP, loopback not set, keepalive set (10 sec)
LCP Open
Open: IPCP, CDPCP
Last input 00:00:06, output 00:00:06, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0 (size/max/drops); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/2/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
34 packets input, 1303 bytes, 0 no buffer
Received 34 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
72 packets output, 2819 bytes, 0 underruns
0 output errors, 0 collisions, 14 interface resets
0 output buffer failures, 0 output buffers swapped out
41 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
RouterA#
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The debug ppp chap command displays the CHAP packet exchanges and PAP
exchanges. The following output displays an example of the authentication
handshake sequence:
RouterA# debug ppp chap
Serial0: Unable to authenticate. No name received from peer
Serial0: Unable to validate CHAP response.
USERNAME pioneer not found.
Serial0: Unable to validate CHAP response.
No password defined for USERNAME pioneer
Serial0: Failed CHAP authentication with remote.
Remote message is Unknown name
Serial0: remote passed CHAP authentication.
Serial0: Passed CHAP authentication with remote.
Serial0: CHAP input code = 4 id = 3 len = 48
The debug ppp chap command displays the reason why the CHAP request
failed.
Once you have finished examining the debug output, use the no debug all
command to turn off the debugging feature.
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ISDN Overview.
ISDN refers to the call-processing system that enables voice, data, and video to
be transmitted over our existing telephone system. ISDN offers several
advantages over existing analog modem lines. For example, ISDN connection
speeds begin at 64Kbps, whereas typical modem speeds hover between
28.8Kbps and 56Kbps. The call setup time for an ISDN call is also much quicker.
ISDN can transmit data packets, voice, or video. ISDN is a viable solution for
remote connectivity (telecommuting) and access to the Internet. ISDN also
supports any of the Network layer protocols supported by the Cisco Internetwork
Operating System (IOS) and encapsulates other WAN services, such as PPP.
Configuring ISDN
You must perform both global and interface configuration tasks when configuring
a router for ISDN. Global configuration tasks include specifying the type of ISDN
switch your router connects to at the provider's central office (CO) and defining
what type of traffic is interesting. Table 4 lists the ISDN global configuration
commands.
Table 4. ISDN Global Configuration Commands
Command
Description
ISDN
switch-type Defines an ISDN switch type
switch-type
dialer-list dialer-group Defines or restricts (permits or denies)
protocol
protocol permit
Defines any specific protocol traffic as interesting for
a particular dialer group
Table 5 shows the ISDN commands that must be configured on an interface.
Table 5. ISDN Interface Configuration Commands
Command
interface bri interface
number
encapsulation ppp
dialer-group number
dialer map protocol
next hop
address
name
hostname speed
number dial-string
dialer
idle-timeout
number
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Description
Chooses the router interface acting as a TE1 device
Chooses PPP framing
Assigns an interface to a specific dialer group
Maps a Layer 3 protocol to a next hop address with a
specific name
Defines the connection speed
Defines the telephone number to dial
Defines the number of seconds of idle time before
the ISDN connection is terminated
218
Figure 5 presents a simple ISDN DDR configuration for router A and router B.
Figure 5. DDR configuration example.
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Monitoring ISDN
The commands listed in this section enable you to monitor the activity and
operation of ISDN and DDR configurations.
You can monitor ISDN and DDR configurations with the following commands:
 show controller bri
 show interface bri
 show dialer
Use the show controller bri command to display detailed information about the B
and D channels. The following output displays an example of the show controller
command:
RouterA# show controller bri 0
BRI unit 0
D Chan Info:
Layer 1 is ACTIVATED
idb 0x32089C, ds 0x3267D8, reset_mask 0x2
buffer size 1524
RX ring with 2 entries at 0x2101600 : Rxhead 0
00 pak=0x4102E8 ds=0x410444 status=D000 pak_size=0
01 pak=0x410C20 ds=0x410D7C status=F000 pak_size=0
TX ring with 1 entries at 0x2101640: tx_count = 0,
tx_head = 0, tx_tail = 0
00 pak=0x000000 ds=0x000000 status=7C00 pak_size=0
0 missed datagrams, 0 overruns, 0 bad frame addresses
0 bad datagram encapsulations, 0 memory errors
0 transmitter underruns
B1 Chan Info:
Layer 1 is ACTIVATED
idb 0x3224E8, ds 0x3268C8, reset_mask 0x0
buffer size 1524
RX ring with 8 entries at 0x2101400 : Rxhead 0
00 pak=0x421FC0 ds=0x42211C status=D000 pak_size=0
01 pak=0x4085E8 ds=0x408744 status=D000 pak_size=0
02 pak=0x422EF0 ds=0x42304C status=D000 pak_size=0
03 pak=0x4148E0 ds=0x414A3C status=D000 pak_size=0
04 pak=0x424D50 ds=0x424EAC status=D000 pak_size=0
05 pak=0x423688 ds=0x4237E4 status=D000 pak_size=0
06 pak=0x41AB98 ds=0x41ACF4 status=D000 pak_size=0
07 pak=0x41A400 ds=0x41A55C status=F000 pak_size=0
TX ring with 4 entries at 0x2101440: tx_count = 0,
tx_head = 0, tx_tail = 0
00 pak=0x000000 ds=0x000000 status=5C00 pak_size=0
01 pak=0x000000 ds=0x000000 status=5C00 pak_size=0
02 pak=0x000000 ds=0x000000 status=5C00 pak_size=0
03 pak=0x000000 ds=0x000000 status=7C00 pak_size=0
0 missed datagrams, 0 overruns, 0 bad frame addresses
0 bad datagram encapsulations, 0 memory errors
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0 transmitter underruns
B2 Chan Info:
Layer 1 is ACTIVATED
idb 0x324520, ds 0x3269B8, reset_mask 0x2
buffer size 1524
RX ring with 8 entries at 0x2101500 : Rxhead 0
00 pak=0x40FCF0 ds=0x40FE4C status=D000 pak_size=0
01 pak=0x40E628 ds=0x40E784 status=D000 pak_size=0
02 pak=0x40F558 ds=0x40F6B4 status=D000 pak_size=0
03 pak=0x413218 ds=0x413374 status=D000 pak_size=0
04 pak=0x40EDC0 ds=0x40EF1C status=D000 pak_size=0
05 pak=0x4113B8 ds=0x411514 status=D000 pak_size=0
06 pak=0x416ED8 ds=0x417034 status=D000 pak_size=0
07 pak=0x416740 ds=0x41689C status=F000 pak_size=0
TX ring with 4 entries at 0x2101540: tx_count = 0,
tx_head = 0, tx_tail = 0
00 pak=0x000000 ds=0x000000 status=5C00 pak_size=0
01 pak=0x000000 ds=0x000000 status=5C00 pak_size=0
02 pak=0x000000 ds=0x000000 status=5C00 pak_size=0
03 pak=0x000000 ds=0x000000 status=7C00 pak_size=0
0 missed datagrams, 0 overruns, 0 bad frame addresses
0 bad datagram encapsulations, 0 memory errors
0 transmitter underruns
Both B channels and the D channel are active.
Use the show interface bri command to display BRI status, encapsulation, and
counter information. The following output displays an example of the show
interface command:
RouterA# show interface bri 0
BRI0 is up, line protocol is up (spoofing)
Hardware is BRI
Internet address is 172.16.67.1, subnet mask is 255.255.255.0
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,
rely 255/255, load 1/255
Encapsulation PPP, loopback not set, keepalive set (10 sec)
Last input 0:00:07, output 0:00:00, output hang never
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
Five minute input rate 0 bits/sec, 0 packets/sec
Five minute output rate 0 bits/sec, 0 packets/sec
16263 packets input, 1347238 bytes, 0 no buffer
Received 13983 broadcasts, 0 runts, 0 giants
2 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 2 abort
22146 packets output, 2383680 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets, 0 restarts
1 carrier transitions
The encapsulation type is PPP, and two errors were received on the BRI.
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Use the show dialer bri command to display general diagnostic information for
serial interfaces configured to support DDR. The following output displays an
example of the show dialer command:
RouterA# show dialer interface bri 0
BRI0 - dialer type = IN-BAND NO-PARITY
Idle timer (900 secs), Fast idle timer (20 secs)
Wait for carrier (30 secs), Re-enable (15 secs)
Time until disconnect 838 secs
Current call connected 0:02:16
Connected to 8986
Dial String
8986
8986
Successes Failures
0
0
8
3
Last called
never
0:02:16
Last status
Success
Default
Default
"IN-BAND" indicates that DDR is enabled and the router is currently connected.
The Dial String table provides a history of logged calls.
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Configuring Frame Relay.
Configuring a Cisco router to serve as a DTE (Data Terminal Equipment) device
within a Frame Relay network involves configuring interfaces on the router. Table
6 lists the commands you must execute to configure Frame Relay on an
interface.
Table 6. Frame Relay Basic Configuration
Command
Description
encapsulation frame- Enables Frame Relay encapsulation; default setting is
relay [cisco | ietf]
"cisco"; "ietf" (see RFC 1490) enables connections to
non-Cisco equipment
frame-relay
lmi-type Sets the Local Management Interface (LMI)
[ansi | cisco | q933a]
type;default setting is "cisco"
In configurations where inverse ARP is not used to dynamically discover network
protocol addresses on the virtual circuit, the frame-relay map command must be
used to map the Layer 3 protocol address to the Layer 2 DLCI.
Configure the frame-relay map command as follows:
Frame-relay map protocol protocol-address dlci [broadcast]
[cisco | ietf]
In this example, protocol is a supported protocol, such as IP or IPX, protocoladdress is the destination protocol address, and dlci is the DLCI number used to
connect to the specified protocol address on the interface. Also, broadcast
(optional) forwards broadcasts to this address (although this is optional, it's
usually a good idea to include it), and ietf (optional) uses the Internet Engineering
Task Force (IETF) form of Frame Relay encapsulation (use this parameter when
the router or access server is connected to another vendor's equipment across a
Frame Relay network). Finally, cisco (optional) is the Cisco encapsulation
method.
NonBroadcast MultiAccess.
Because Frame Relay connections are established by direct Permanent Virtual
Circuits (PVCs), Frame Relay cannot support broadcast transmissions. If
broadcast services are required, a router must copy the broadcast and then
transmit it on each of its PVCs. The term that describes this behavior is
NonBroadcast MultiAccess (NBMA). NBMA simply describes any multiaccess
Layer 2 protocol that does not provide a mechanism for broadcasting messages
(such as route updates between routers). For broadcast messages to be
communicated in an NBMA network, each router within the network serves as a
peer and is part of the same subnet. In a Frame Relay network, broadcast
messages must be duplicated and then send out each PVC to each peer.
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Subinterfaces
A single, physical serial interface can be configured with several virtual interfaces
called subinterfaces. These subinterfaces can be configured on a serial line;
different information is sent and received on each serial subinterface. Using
subinterfaces, a single router can support PVCs to several other routers. Figure 6
depicts a simple Frame Relay network with subinterfaces.
Figure 6. A simple frame relay network.
Before configuring a subinterface for a Frame Relay network, the Frame Relay
configuration on the physical interface must be complete. Execute the following
command to create a subinterface and assign it a DLCI value:
Interface type .subinterface point-to-point
Frame-relay interface-dlci dlci [broadcast]
In this command, type is the physical serial interface number, subinterface is the
subinterface number, dlci is the DLCI number used to connect to the specified
protocol address on the interface, and broadcast (optional) forwards broadcasts
to this address. A common practice in choosing subinterface numbers is to use
the same number as the DLCI value.
TIP:
The proper syntax for creating and accessing a subinterface is the interface
number followed by a period (.) followed by the subinterface number. For
example, serial 0.11 indicates subinterface 11 on serial interface 0.
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Monitoring Frame Relay.
After the Frame Relay configuration is complete, you can use the show interface
and debug frame-relay commands to monitor and troubleshoot the configuration.
The following output shows the results of the show interface command:
Router# show interface serial 0
Serial0 is up, line protocol is up
Hardware is MCI Serial
Internet address is 172.59.1.1,
subnet mask is 255.255.255.252
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 249/255,
load 1/255
Encapsulation FRAME-RELAY, loopback not set,
keepalive set (10 sec)
LMI enq sent 4, LMI stat recvd 0, LMI upd recvd 0,
DTE LMI UP
LMI enq recvd 268, LMI stat sent 264, LMI upd sent 0
LMI DLCI 1023 LMI type is CISCO frame relay DTE
Last input 0:00:09, output 0:00:07, output hang never
Last clearing of "show interface" counters 0:44:57
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
Five minute input rate 0 bits/sec, 0 packets/sec
Five minute output rate 0 bits/sec, 0 packets/sec
309 packets input, 6641 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants
0 input errors, 0 CRC, 0 frame, 0 overrun,
0 ignored, 0 abort
0 input packets with dribble condition detected
268 packets output, 3836 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets,
0 restarts
180 carrier transitions
Use the show frame-relay pvc command to display the status of the virtual circuit,
as shown in the following:
RouterA#show frame-relay pvc
PVC Statistics for interface Serial0 (Frame Relay DTE)
DLCI = 222, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE,INTERFACE =
Serial0
input pkts 50
output pkts 20
in bytes 11431
out bytes 1474
dropped pkts 2
in FECN pkts 0
in BECN pkts 0
out FECN pkts 0
out BECN pkts 0
in DE pkts 0
out DE pkts 0
pvc create time 04:14:10, last time pvc status changed 00:39:06
RouterA#
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Use the show frame-relay lmi command to determine whether LMI is being
transmitted successfully:
RouterA#show frame-relay lmi
LMI Statistics for interface Serial0
(Frame Relay DTE) LMI TYPE = CISCO
Invalid Unnumbered info 0
Invalid dummy Call Ref 0
Invalid Status Message 0
Invalid Information ID 0
Invalid Report Request 0
Num Status Enq. Sent 292
Num Update Status Rcvd 0
RouterA#
Invalid Prot Disc 0
Invalid Msg Type 0
Invalid Lock Shift 0
Invalid Report IE Len 0
Invalid Keep IE Len 0
Num Status msgs Rcvd 292
Num Status Timeouts 0
Use the show frame-relay map command to display mappings among protocol,
protocol address, and DLCI, as shown in the following:
RouterA#show frame-relay map
Serial0 (up): ip 172.59.1.1 dlci 222(0xDE,0x34E0), dynamic,
broadcast, status defined, active
RouterA#
The debug frame-relay command enables you to monitor the Frame Relay
activity closely. The debug frame-relay lmi command enables you to monitor LMI
activity on a router closely. The following output shows sample output from the
debug frame-relay lmi command.
RouterA#debug frame-relay lmi
Frame Relay LMI debugging is on
RouterA#
Serial0(out): StEnq, myseq 20, yourseen 67, DTE up
datagramstart = 0x23A3820, datagramsize = 13
FR encap = 0xFCF10309
00 75 01 01 01 03 02 14 43
Serial0(in): Status, myseq 20
RT IE 1, length 1, type 1
KA IE 3, length 2, yourseq 68, myseq 20
RouterA#
Serial0(out): StEnq, myseq 21, yourseen 68, DTE up
datagramstart = 0x23A3820, datagramsize = 13
The sequence counters for the LMI transmission are being increased properly.
Enabling a single debug command on a router does not use much of the router's
system resources; however, enabling several debug commands may severely
affect the router's ability to perform its functions. The no debug all command
quickly disables all debug commands on a router.
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Upgrading Cisco IOS Software.
Cisco IOS is constantly being revised to add new features or to fix bugs in
previous versions. The process of upgrading software on a Cisco router can be
broken down into three main steps:
1. Back up the current Cisco IOS.
2. Copy the new Cisco IOS to the router.
3. Reload the Cisco router and verify the new IOS.
Backing Up the Current IOS
The first part of backing up the current IOS involves determining what version of
IOS is running on the router and the filename of the software image. It is also
necessary to note the size available in Flash memory. The new version of IOS
must not be larger than the total Flash memory on the router. The show version
command displays this information, as shown here:
NFLD#sh vers
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-J-L), Version 11.2(13),
RELEASE SOFTWARE (fc1)
Copyright (c) 1986-1998 by cisco Systems, Inc.
Compiled Tue 31-Mar-98 10:27 by tlane
Image text-base: 0x0303F1E4, data-base: 0x00001000
ROM: System Bootstrap, Version 11.0(10c)XB1,
PLATFORM SPECIFIC RELEASE SOFTWARE (fc1)
BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R),
Version 11.0(10c)XB1,
PLATFORM SPECIFIC RELEASE SOFTWARE (fc1)
NFLD uptime is 7 minutes
System restarted by reload
System image file is "flash:11-2-13.img", booted via flash
cisco 2500 (68030) processor (revision L)
with 2048K/2048K bytes of memory.
Processor board ID 07110268, with hardware revision 00000000
Bridging software.
SuperLAT software copyright 1990 by Meridian Technology Corp.
X.25 software, Version 2.0, NET2, BFE and GOSIP compliant.
TN3270 Emulation software.
2 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2102
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From the preceding command listing, we can determine that we have 16,384KB
of Flash memory available. Therefore, we can copy any software image less than
or equal to 16,384KB to this device. The name of the file is provided as "11-213.img." After the memory requirements and the filename have been determined,
we need to copy the old image to a TFTP server. This step gives us a fallback
procedure in case the new software image is corrupt:
TIP:
In the following example, the exclamation mark indicates the system is working.
In other examples, you will see the letter "e" (erasing) repeated as the system
works on a command. The repeated letters simply mean you should be patient
and let the system complete the current command before entering another one.
NFLD#copy flash TFTP
System flash directory:
File Length Name/status
1 7969232 11-2-13.img
[7969296 bytes used, 8807920 available, 16777216 total]
Address or name of remote host [255.255.255.255]? 172.16.24.134
Source file name? 11-2-13.img
Destination file name [11-2-13.img]? <Return>
Verifying checksum for '11-2-13.img' (file # 1)... OK
Copy '11-2-13.img' from Flash to server
as '11-2-13.img'? [yes/no]y
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Upload to server done
Flash copy took 00:04:36 [hh:mm:ss]
Upgrading the IOS
After the current IOS has been backed up to a TFTP server and the available
memory on the router has been checked, we can proceed with the upgrade of
the IOS. The new IOS must reside on the TFTP server, as shown here:
NFLD#copy TFTP flash
Proceed? [confirm]<Return>
System flash directory:
File Length Name/status
1 7969232 11-2-14.img
[7969296 bytes used, 8807920 available, 16777216 total]
Address or name of remote host [172.16.24.134]?<RETURN>
Source file name? 11-2-14.img
Destination file name [11-2-14.img]?<RETURN>
Accessing file '11-2-14.img' on 172.16.24.134...
Loading 11-2-14.img from 172.16.24.134 (via Ethernet1): !
[OK]<RETURN>
Erase flash device before writing? [confirm]<RETURN>
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Flash contains files. Are you sure you want to erase?
[confirm]<RETURN>
System configuration has been modified. Save? [yes/no]: <RETURN>
% Please answer 'yes' or 'no'. Y
System configuration has been modified. Save? [yes/no]: y
Building configuration...
[OK] <RETURN>
Copy '11-2-14.img' from server
as '11-2-14.img' into Flash WITH erase? [yes/no]y
%SYS-5-RELOAD: Reload requested
%SYS-4-CONFIG_NEWER: Configurations from version 11.2 may not be
correctly understood.
%FLH: 11-2-14.img from 172.16.24.134 to flash ...
System flash directory:
File Length Name/status
1 7969232 11-2-14.img
[7969296 bytes used, 8807920 available, 16777216 total]
Accessing file '11-2-14.img' on 172.16.24.134...
Loading 11-2-14.img from 172.16.24.134 (via Ethernet1): ! [OK]
Erasing device...
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
...erased
Loading 11-2-14.img from 172.16.24.134 (via Ethernet1): !!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
[OK - 7969232/16777216 bytes]
Verifying checksum... OK (0xF865)
Flash copy took 0:07:00 [hh:mm:ss]
Reloading the Router
Depending on what type of router mode we have, when we copy a new version
of software to the router, the router will either reload itself or return with the
Router# prompt. If the router returns with a prompt, we use the Router# reload
command to restart the router and load the new software. The router reload
command is as follows:
Router# reload
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Routing Protocol Configuration and Review.
This section highlights the basic router commands necessary to add the RIP and
IGRP to a router configuration.
RIP
Table 7 lists the configuration commands necessary to enable RIP on a router.
Table 7. RIP Configuration Commands
Task
Router Command
RouterA#configure terminal
Enter global configuration mode
Enter RIP configuration mode
RouterA (config)#router rip
Configure network 172.16.0.0 to be RouterA
(config-router)#network
advertised
172.16.0.0
Exit configuration mode
RouterA (config-router)#<CTRL>Z
The show IP protocol command displays detailed information about each IP
routing protocol that has been configured on the router.
The following output displays the results of the show IP protocol command after
RIP has been configured:
RouterA#show ip protocol
Routing Protocol is "rip"
Sending updates every 30 seconds, next due in 2 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Redistributing: rip
Default version control: send version 1, receive any version
Interface
Send Recv
Key-chain
Ethernet0
1
1
2
Loopback0
1
1
2
Serial0
1
1
2
Routing for Networks:
172.16.0.0
Routing Information Sources:
Gateway
Distance
Last Update
172.16.24.252
120
00:00:12
Distance: (default is 120)
RouterA#
By default, RIP sends updates every 30 seconds. Also, the RIP hold-down timer
is set to 180 seconds, and a neighbor router has an IP address of 172.16.24.252.
IGRP
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Table 8 lists the configuration commands necessary to enable IGRP on a router.
Table 8. Configuring IGRP
Task
Enter global configuration mode
Enter IGRP routing protocol configuration
mode for autonomous system 1
Configure network 172.16.0.0 to be
advertised
Exit configuration mode
Router Syntax
RouterA#configure terminal
RouterA(config)#router igrp 1
RouterA(config-router)#network
172.16.0.0
RouterA
(configrouter)#<CTRL>Z
The following output displays the results of the show IP protocol command after
IGRP has been configured.
RouterA#show ip protocol
Routing Protocol is "igrp 1"
Sending updates every 90 seconds, next due in 7 seconds
Invalid after 270 seconds, hold down 280, flushed after 630
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
IGRP maximum hopcount 100
IGRP maximum metric variance 1
Redistributing: igrp 1
Routing for Networks:
172.16.0.0
Routing Information Sources:
Gateway
Distance
Last Update
172.16.24.252
100
00:00:15
Distance: (default is 100)
RouterA#
By default, IGRP sends updates every 90 seconds. Also, the IGRP maximum
hop count is set to 100, and a neighbor router has an IP address of
172.16.24.252.
The next section of this chapter covers access lists for IP and IPX traffic. Access
lists allow network administrators to restrict access to certain networks, devices,
and services. They provide an effective means of applying security within an
organization; they also permit or deny specific types of traffic to pass through an
interface. The types of IP traffic they filter can be based on source or destination
address or address range, protocol, precedence, type of service, icmp-type,
icmp-code, icmp-message, igmp-type, port, or state of the TCP connection. A full
list of access lists is provided in Table 9.
Cisco CCNA (640-801).doc
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Table 9. Types of access lists.
Numeric Range
1 through 99
100 through 199
200 through 299
300 through 399
600 through 699
700 through 799
800 through 899
900 through 999
1000 through 1099
Description
IP standard access list
IP extended access list
Ethernet access list
DECnet access list
AppleTalk access list
48-bit media access control (MAC) address access list
IPX standard access list
IPX extended access list
Service Access Point (SAP) access list
Access lists provide a powerful set of tools that can deny and permit users to
access specific applications or hosts. The tradeoff for using access lists,
however, is that they require processing power to compare packets entering or
exiting an interface with the entries in the list.
A wide variety of access lists can be applied to a router interface. This chapter
focuses only on the IP standard and extended access lists, IPX SAP access lists,
and IPX standard and extended access lists.
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IP Access Lists.
IP access lists are used to deny or permit specific traffic into or out of an interface
on a router. They filter IP source and destination addresses and protocol- or
service-specific traffic. IP access lists are of two types: standard and extended.
The difference between the two is the precision by which each can filter IP traffic.
IP Standard Access Lists
IP standard access lists filter traffic based on the source IP address or address
range. Therefore, administrators can use this tool to restrict access to specific
users and allow access to others. The lists are applied to the interface of a router
where traffic is to be filtered, and they restrict access into or out of the interface.
The direction in which traffic is restricted is determined by the Cisco command
used to apply the access list to the interface.
IP Standard Access List Commands
Creating and applying an access list to an interface consists of two steps, both of
which are performed in the configuration mode of a router. First, the access list
must be created. A single access list can consist of many access list statements.
An access list number identifies an individual access group, which can consist of
many access list entries. In addition, the order in which access list entries are
created plays an important role in the behavior of the access list. When traffic
passes through the interface, it is compared with each access list entry in the
order in which the entries were created. If the traffic matches an access list entry,
the indicated function (permit or deny) of the access list entry is performed on the
traffic. When a packet is permitted entry, the router caches the entry, and any
subsequent packets in this session are granted access without being applied
against the access list. All access lists have an implicit deny all statement at the
end. Therefore, if the traffic does not match any entry, it is denied access into or
out of the interface. The command to create an access list is as follows:
Access-list access-list-number {deny|permit} source
[source-wildcard]
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A brief description of each field is provided in Table 10.
Table 10. IP Standard Access List Command Field Descriptions
Identifier
access-listnumber
deny
permit
source
source-wildcard
Description
A dotted decimal number between 1 and 99
Denies access if condition is matched
Permits access if condition is matched
Number of the network or host from which the packet is
being sent
Wildcard bits to be applied to the source
TIP:
Any time you are working with access lists, remember the implicit deny
automatically incorporated into the list. That is, anything you do not specifically
identify as accepted is by default denied.
The source-wildcard field, referred to as a wildcard mask, is used to identify bits
in an IP address that have meaning and bits that can be ignored. In this case, the
wildcard mask is referred to as a source-wildcard, indicating that it is a wildcard
mask of the source IP address. A source-wildcard mask is applied to a source IP
address to determine a range of addresses to permit or deny.
At first, the best way to learn wildcard masks is to convert them from decimal to
binary format. The wildcard mask is applied by comparing the IP address bits
with the corresponding IP wildcard bits. A 1 bit in the wildcard mask indicates that
the corresponding bit in the IP address can be ignored. Therefore, the IP address
bit can be either 1 or 0. A 0 in the wildcard mask indicates that the corresponding
bit in the IP address must be strictly followed. Tables 10.3 and 10.4 illustrate how
to apply a source-wildcard mask to a source address to determine a range of
addresses.
Tables 3 and 4 illustrate that the first three octets must be strictly followed;
therefore, the values of these octets must be 172.16.16 to be a match. The 1 bits
in the fourth octet, however, indicate that any value between 0 and 255 will result
in a match. Therefore, any host with the IP address of 172.16.16.0 through
172.16.16.255 is a match for this source IP address and source-wildcard mask.
The next step is to apply the access list to an interface. The syntax for doing so is
as follows:
NFLD(config-if)#ip access-group access-list-number {in|out}
Here, access-list-number is the number used to identify the access list. This
number must be the same as the one specified in the access-list command used
to create the previously shown entries. The in|out option indicates whether this
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list is to filter on inbound or outbound traffic through the interface. It is important
to remember that the access list is being applied to a specific interface on a
router, rather than to all the interfaces on the router.
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Creating and Applying an IP Standard Access List.
The network shown in Figure 7 is used to illustrate IP standard access lists.
Figure 7. Configuring a standard access list.
In this example, suppose you want to permit the following devices to have access
to network 172.16.4.0:
 Any device on network 172.16.14.0
 Any device on network 172.16.3.0 except 172.16.3.5
 Only the device with the IP address of 172.16.12.4 on network
172.16.12.0
Applying an IP standard access list to a router interface involves two steps. The
first step is to create the access list to indicate all the source addresses that are
permitted or denied access. The second step is to apply the access list to the
interface on which you are restricting either outbound or inbound traffic. By
applying the access-group command to interface Ethernet 0, you can restrict
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access to network 172.16.4.0. The commands to create this access list are as
follows:
NFLD#configure terminal
NFLD(config)#access-list
NFLD(config)#access-list
NFLD(config)#access-list
NFLD(config)#access-list
NFLD(config)#access-list
5
5
5
5
5
permit 172.16.14.0 0.0.0.255
deny 172.16.3.5 0.0.0.0
permit 172.16.3.0 0.0.0.255
permit 172.16.12.4 0.0.0.0
deny 0.0.0.0 255.255.255.255
These commands restrict and permit the traffic detailed in the requirements. The
first access-list enTRy permits access to all users from network 172.16.14.0 to
pass through the access list on Ethernet 0. Note that the source-wildcard of
0.0.0.255 indicates that every host ID in the last octet can be ignored, thus
allowing all IP addresses between 172.16.14.0 and 172.16.14.255 access. The
second access-list command denies host ID 172.16.3.5 to pass through the
access list. Note that the source-wildcard of 0.0.0.0 indicates that only the source
address specified (172.16.3.5) is denied access. The third access-list command
permits all users on network 172.16.3.0 to pass through the access list. Note that
host ID 172.16.3.5 will still not be allowed to pass through the access list,
because any traffic from this host was dropped by the previous deny command.
The order in which a permit or deny command is placed in an access list is
extremely important.
When adding new entries to existing access lists, it is sometimes necessary to
reorder the access list so that it will filter traffic correctly. Often, the best way to
reorder the entries is to copy all the entries into a text file, add or remove the
required entries, and reorder them in that text file. After you have them ordered
correctly, add them all to the router configuration.
The fourth access-list enTRy permits only user 172.16.12.4 to pass through the
access list. Finally, the last access-list command is implicit whenever an access
list is created; therefore, any packet not generated by the router with the access
list that does not match one of the permit entries is dropped. You do not have to
configure this deny entry.
Before these access list entries can filter traffic, they must be applied to the
interface as an access group. The access lists are going to be applied to
outbound packets on Ethernet 0. Therefore, any packet attempting to travel out
interface Ethernet 0 must match one of the entries in access group 5. The steps
to configure an outbound access list on Ethernet 0 are as follows:
NFLD#config t
Enter configuration commands, one per line. End with CNTL/Z.
NFLD(config)#interface ethernet 0
NFLD(config-if)#ip access-group 5 out
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Here, access-group 5 has been applied to the outbound Ethernet 0 interface.
Now, every packet that is sent out the Ethernet 0 interface will be checked to see
if it matches.
More complicated scenarios for restricting access through an interface exist.
Sometimes a network administrator wants to permit only a range of IP addresses
through an access list. However, it is more complicated to permit access to a
range of IP addresses that do not fall exactly on octet bit boundaries. A second
example follows to illustrate this scenario.
Continue to use the network provided in Figure 7; however, in this case, you
want to allow devices to have access only to network 172.16.4.0. Therefore, you
want to permit access to any device with the IP address between 172.16.3.32
and 172.16.3.39.
For this scenario, you must determine the proper source-wildcard mask to apply
to allow access to devices in the IP address range 172.16.3.32 through
172.16.3.39. Start with the IP address 172.16.3.32 to create this access list.
Next, apply a network mask that allows eight incremental bits in the fourth octet.
Table 10 illustrates the proper source IP address and source wildcard in binary
and decimal format for this example.
Table 10 illustrates that by applying the source-wildcard mask of 0.0.0.7, a range
of IP addresses that do not fall on an octet boundary has been allowed.
Table 10a. Applying a Source-wildcard Mask to a Source IP Address
in Binary Format
Source Address in
Bits
Source address
Source-wildcard
Permitted address 1
Permitted address 2
Permitted address 3
Permitted address 4
Permitted address 5
Permitted address 6
Permitted address 7
Permitted address 8
Cisco CCNA (640-801).doc
Binary
Decimal
10101100.00010000.00000011.00100000
00000000.00000000.00000000.00000111
10101100.00010000.00010000.00100000
10101100.00010000.00010000.00100001
10101100.00010000.00010000.00100010
10101100.00010000.00010000.00100011
10101100.00010000.00010000.00100100
10101100.00010000.00010000.00100101
10101100.00010000.00010000.00100110
10101100.00010000.00010000.00100111
172.16.3.32
0.0.0.7
172.16.3.32
172.16.3.33
172.16.3.34
172.16.3.35
172.16.3.36
172.16.3.37
172.16.3.38
172.16.3.39
238
Each permitted address is determined by taking the bits indicated as ignored bits
by the source-wildcard mask and listing the possible permutations. Here are a
few good rules to know:
 When you're grouping IP addresses, the group size is always a power of 2
(2, 4, 8, 16, and so forth).
 Any time IP addresses are grouped together, the first IP address in the
group is divisible by the size of the group. For example, a group of eight IP
addresses can start only on multiples of eight (8, 16, 24, and so forth).
 The wildcard mask is always one less than the group size. For example, a
group of eight has a wildcard mask of seven. A group of 64 has a wildcard
mask of 63.
Although IP standard access lists provide a powerful set of tools for restricting
access, they can only restrict access based on the source IP address. IP
extended access lists increase the variables that can be used to restrict access
through an interface.
IP Extended Access Lists
IP standard access lists filter traffic based on the source IP address only;
therefore, administrators can use this tool to restrict access to specific users only.
Because administrators wanted more control of the traffic that could travel
through interfaces, Cisco responded with IP extended access lists, which perform
the same basic function as standard access lists (permitting and denying IP
packets through an interface) but extend the types of IP traffic that can be
filtered. Consequently, IP extended access lists allow for more precise filtering of
IP traffic. Whereas IP standard access lists allow only source IP address filtering,
IP extended access lists provide source and destination IP address filtering. In
addition, IP extended access lists filter on Layer 4 protocols, such as
Transmission Control Protocol (TCP) and User Datagram Protocol (UDP); look
into the TCP or UDP header; and allow filtering on TCP/UDP port numbers.
In addition, IP extended access lists allow filtering based on the IP precedence
field, TOS field, icmp-type, icmp-code, icmp-message, igmp-type, and TCPestablished connections. This book covers only source and destination address,
IP protocol, and TCP/UDP port numbers.
IP Extended Access List Commands
The steps taken to create and apply an IP extended access list are the same as
those used for an IP standard access list. First, create the access list entries.
Second, apply the access list group to the interface where you want to filter
traffic.
TIP:
It is important to enter IP extended access list entries in the correct order. Also,
an implicit deny all traffic entry is at the end of every IP extended access list.
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The command to create an IP extended access list is very similar to the
command used to create an IP standard access list. However, the additional
filtering capabilities require some additional fields in the command. The
command to create an access list is as follows:
access-list access-list-number {deny|permit} protocol source
source-wildcard [operator port [port]] destination [destinationwildcard] [operator port [port]]
Because how to read the command list was covered in the IP standard access
list section, only the additional fields are discussed here. The first noticeable
difference is the addition of the protocol field. This field is typically filled with TCP
or UDP (other possibilities exist, but these are beyond the scope of this book and
the CCNA exam). The operator port [port] field is used to indicate the TCP/UDP
port or range of ports for the source and source-wildcard fields. In addition, the
destination and destination-wildcard fields are added with their corresponding
operator port [port] field. Basically, the fields necessary to filter traffic on source
and destination addresses, the IP protocol (TCP or UDP), and port numbers
have been added. In addition, the access-list-number field must now be a
number between 100 and 199, as indicated in Table 8. A complete list of all of
the fields in the IP extended access list command is provided in Table 11.
Table 11. Access List Command Field Descriptions
Access List
Command
access list-number
deny
permit
protocol
source
source-wildcard
destination
destination-wildcard
precedence
tos
icmp-type
icmp-code
icmp-message
igmp-type
operator
port
established
log
Cisco CCNA (640-801).doc
Description
Identifies the access list for which it belongs
Denies access if condition is matched
Permits access if condition is matched
Name or number of the IP protocol
Number of the network or host from which the packet is
being sent
Wildcard bits to be applied to the source
Number of the network or host from which the packet
originated
Wildcard bits to be applied to the destination
Filter packets by precedence level
Filter packets by type of service
Filter packets by icmp-type
Filter packets by icmp-code
Filter packets by icmp-message
Filter packets by igmp-type
Compares source or destination ports
Decimal value or name of a TCP or UDP port
Indicates an established connection
Causes an information logging entry
240
To apply an IP extended access list, use the same IP access group command
that is used for standard access lists. Simply apply the access list to the interface
where you want to filter traffic.
Creating and Applying an IP Extended Access List
To illustrate the use of the IP extended access list functionality, continue to use
the network shown in Figure 7. In this example, you want to extend the types of
traffic being filtered. Suppose you want to permit the following traffic to pass
through your access list:
 Any device on network 172.16.14.0 is permitted to communicate with any
device on network 172.16.4.0 using IP, TCP, and port number 23 (Telnet).
 Device 172.16.14.2 is permitted to communicate with device 172.16.4.4
using IP, UDP, and UDP port number 69 (TFTP).
 Device 172.16.14.3 is permitted to communicate with any device on any
network using IP and TCP for any port number.
The following commands create this access list:
NFLD#configure terminal
NFLD(config)#access-list 105 permit tcp 172.16.14.0 0.0.0.255
172.16.4.0 0.0.0.255 eq 23
NFLD(config)#access-list 105 permit udp host 172.16.14.2
host 172.16.4.4 eq 69
NFLD(config)#access-list 105 permit tcp host 172.16.14.3 any
any
NFLD(config)#access-list 105 deny any any
Let's discuss these access list entries. The first entry performs the extended
functionality by indicating that only TCP traffic from any device on network
172.16.14.0 (indicated by the source-wildcard mask of 0.0.0.255) is permitted to
communicate with 172.16.4.0 (indicated by the destination-wildcard of 0.0.0.255)
using the TCP port number (indicated by the operator eq and the port number
23). The operator eq stands for "equal to." A subset of the different possible
operators is supplied in Table 12.
Table 12. Extended Access List Command Field Descriptions
Operator
eq
lt
gt
range
Meaning
Match only packets on a given port number
Match only packets with a lower port number
Match only packets with a greater port number
Match only packets in the range of port numbers
The second entry introduces the word "host" into the command; this is a short
way of indicating the wildcard mask 0.0.0.0. However, the "host" word precedes
the IP address, versus the traditional trailing wildcard mask. So, in this entry, only
Cisco CCNA (640-801).doc
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the device with the IP address 172.16.14.2 has been allowed to communicate
with device 172.16.4.4 using the UDP for the port number 69 (TFTP).
The third entry introduces the word "any" into the command. Similar to the word
"host" in the preceding condition, the "any" word is a short way of indicating any
source or destination address with the wildcard mask 255.255.255.255. This
mask indicates that all IP addresses are being described; therefore, it does not
matter what source or destination IP address is specified. In this case, all
destination addresses have been described. So, in this entry, the device with IP
address 172.16.14.3 has been allowed to communicate with any device using the
TCP for any port number.
The last entry in italics is the implicit deny all statement. It is not necessary to add
this entry, because it is always there.
The second step is applying the access list to the interface that you are
restricting. Specify whether you are filtering outbound or inbound traffic by adding
the keyword "out" or "in" to the end of the command. In this example, apply the
access list to Ethernet 1 to illustrate the ability of IP extended access lists to filter
traffic based on destination address as well as source address. The command to
apply the access group to the interface is as follows:
NFLD#config t
Enter configuration commands, one per line. End with CNTL/Z.
NFLD(config)#interface ethernet 1
NFLD(config-if)#ip access-group 105 in
TIP:
Notice that once you have entered configuration mode, you may only enter one
command per line. Also notice that you leave configuration mode by pressing
Cntl+Z. These two aspects of configuration mode have been favorite test
questions.
In summary, extended access lists are used to increase the preciseness of your
filtering. The steps performed to create and apply access lists do not change.
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Monitoring and Verifying Access Lists.
After you have configured all your access lists, it is important that you review
your entries and determine whether you are filtering traffic in the manner
intended. Many different methods exist to monitor and verify access lists. For the
scope of this book and the CCNA exam, we will illustrate only two of the more
basic methods. Refer to the Cisco Command Reference to identify some of the
other methods used to monitor access lists. To determine which access lists you
have applied to specific interfaces, use the show ip interface command as
follows:
NFLD# show ip interface
Ethernet 0 is up, line protocol is up
Internet address is 172.16.4.4, subnet mask is 255.255.255.0
Broadcast address is 255.255.255.255
Address determined by non-volatile memory
No helper address
No secondary address
Outgoing access list 5 is set
Inbound access list is not set
Proxy ARP is enabled
Security level is default
Split horizon is enabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is enabled
Gateway Discovery is disabled
IP accounting is disabled
TCP/IP header compression is disabled
NFLD#
The entry identifying the outbound access list is highlighted. To get a more
detailed look at the type of access lists you have applied, use the show accesslists command as follows:
NFLD>show access-lists
Standard IP access list 5
permit 172.16.14.0, wildcard bits 0.0.0.255
deny 172.16.3.5, wildcard bits 0.0.0.0
permit 172.16.4.0, wildcard bits 0.0.0.255
permit 172.16.12.4, wildcard bits 0.0.0.0
Extended IP access list 105
permit tcp 172.16.14.0 0.0.0.255 172.16.4.0 eq 23
permit udp host 172.16.14.2 host 172.16.4.4 eq 69
permit tcp host 172.16.14.3 any any
deny 0.0.0.0 255.255.255.255
NFLD>
Standard access lists apply to a group of things, whereas extended access lists
apply to a specific port or user.
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Prep Questions
1.
Which of the following commands will allow you to review the contents
of NVRAM? (Choose the two best answers.)
A. show configuration
B. show protocols
C. show version
D. show running-config
E. show startup-config
A1:
The correct answers are A and E. The show configuration and show
startup-config commands display the router's backup configuration file
from NVRAM. The show protocols, show version, and show runningconfig commands will allow you to review the contents of RAM, not
NVRAM. Therefore, answers B, C, and D are incorrect.
2.
Which of the following router components contains the router's IOS
image?
A. Flash memory
B. NVRAM
C. RAM
D. Interfaces
A2:
The correct answer is A. Flash memory contains the IOS images used
by the router. If no image resides in Flash memory, the image in ROM
will be used. NVRAM and RAM contain the backup configuration and
active configuration files, respectively. Therefore, answers B and C are
incorrect. Interfaces provide the network connections for the router.
Therefore, answer D is incorrect.
3.
Which of the following router components contain versions of the
router's configuration file? (Choose the two best answers.)
A. Flash memory
B. NVRAM
C. RAM
D. ROM
A3:
The correct answers are B and C. NVRAM contains the backup
configuration file for the router, whereas RAM contains the router's
active configuration file. Flash memory and ROM do not contain a
configuration file; they contain the router's IOS image files. Therefore,
answers A and D are incorrect.
Cisco CCNA (640-801).doc
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4.
Which of the following commands will allow you to review the contents
of RAM? (Choose the three best answers.)
A. show configuration
B. show protocols
C. show version
D. show running-config
E. show startup-config
A4:
The correct answers are B, C, and D. The show protocols, show
version, and show running-config commands allow you to review the
contents of RAM. The show configuration and show startup-config
commands allow you to review the router's backup configuration file
from NVRAM, not RAM. Therefore, answers A and E are incorrect.
5.
Which command would be used to restore a configuration file to RAM
on a Cisco router?
A. router#copy TFTP running-config
B. router>copy TFTP running-config
C. router#copy TFTP startup-config
D. router>copy TFTP startup-config
A5:
The correct answer is A. To restore a configuration file, the file must be
copied from a TFTP server to the Cisco router. This is a trick question,
because you must be in EXEC privileged mode to perform this function.
Answers B and D are incorrect because the question implies that the
command is initiated from EXEC mode; you can determine this by the >
symbol (as opposed to the # symbol) at the end of the word router in
answers B and D. Answer C is incorrect because the startup
configuration file is not in RAM, and the question requires that you copy
to the running configuration file, which is in RAM.
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6.
Which of the following commands will display the running configuration
file to a console terminal?
A. router>show running-config
B. router#show startup-config
C. router#show flash
D. router>show version
E. None of the above
A6:
The correct answer is A. The command to display a running
configuration file to a console terminal is show running-config. Answer B
displays the startup configuration file to the console monitor and is
therefore incorrect. Answer C is incorrect because it displays any IOS
images or configuration files stored in Flash memory. Answer D
displays the software version and hardware on this router and is
therefore incorrect.
7.
If you need to copy the currently executing configuration file into
NVRAM, which command would accomplish this goal?
A. router#copy startup-config running-config
B. router#copy startup-config TFTP
C. router#copy running-config startup-config
D. router>copy startup-config running-config
A7:
The correct answer is C. The startup configuration file exists in NVRAM.
So, to copy a configuration file to NVRAM, the current startup
configuration file must be overwritten. Answer A is incorrect because
the startup configuration file is not the currently executing image, and
this command is attempting to write the configuration file to RAM.
Answer B is incorrect because the startup configuration file is not the
currently executing configuration file, and TFTP does not exist in
NVRAM. Answer D is incorrect because the startup configuration file is
not the currently executing image and because the command is being
executed from EXEC mode.
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8.
Which of the following commands would not set a password on a Cisco
router?
A. router(config)#enable secret
B. router(config-line)#password NFLD
C. router(config)#service encryption password
D. router(config)#enable password
A8:
The correct answer is C. The service encryption password command is
used to encrypt passwords in configuration files. Answer A is incorrect
because it is used to set the "enable secret password". Answer B is
incorrect because this command is used to set the Telnet, auxiliary, or
console password, depending on which line configuration mode the
router is in when the command is executed. Answer D is incorrect
because it is used to set the "enable password".
9.
In which of the following scenarios would a router boot into the initial
configuration dialog after its power has been cycled? (Choose the two
best answers.)
A. When someone copies the startup configuration file to a TFTP
server.
B. When the running configuration file is copied to the startup
configuration file.
C. When the router is powered on for the first time.
D. When the write erase command is executed immediately before the
router is powered down.
A9:
The correct answers are C and D. The initial configuration dialog starts
anytime a configuration file cannot be found in NVRAM. This occurs
when a write erase command is performed on the startup configuration
file or when the router is being powered on for the first time. Answer A
is incorrect because copying a startup configuration file to a TFTP
server will not cause a router to boot into the initial configuration dialog.
Copying the running configuration file to the startup configuration file will
not cause the router to boot into the initial configuration dialog.
Therefore, answer B is incorrect.
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10.
Which of the following configuration register values would force a router
to boot from ROM?
A. 0x2103
B. 0x210F
C. 0x2101
D. 0x2104
A10:
The correct answer is C. A configuration register with the value 0x2101
forces a router to boot from ROM. Only when the boot field has a value
of 1 or 0 will the router boot from ROM. Answers A, B, and D are
incorrect because all these values would cause the router to look at the
boot commands in the configuration file to determine what IOS to load.
11.
Where does the running configuration file exist in a Cisco router?
A. NVRAM
B. ROM
C. RAM
D. Flash memory
A11:
The correct answer is C. The running configuration file exists in RAM.
This file is erased when a router is reloaded or its power is cycled.
Answer B cannot be correct because ROM is a read-only device, and
configuration files are constantly being updated. Answer A is incorrect
because NVRAM is used to maintain the startup configuration file, not
the running configuration file. Answer D is incorrect because Flash
memory stores a copy of the IOS software, not the running
configuration files.
12.
Which is the correct command to back up Cisco IOS software?
A. router#copy running-config startup-config
B. router(config)#copy TFTP flash
C. router#copy flash TFTP
D. router#copy flash NVRAM
A12:
The correct answer is C. To back up Cisco IOS software, you must
copy it to a TFTP server or another storage device. Answer A is
incorrect because this command deals with configuration files, not
Cisco IOS software. Answer B is incorrect because this command
would be used to restore the Cisco IOS to a router. Answer D is
incorrect because copy flash NVRAM is not a valid command.
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13.
Which of the following is not a valid Cisco command?
A. router>show version
B. router#show running-config
C. router#show startup-config
D. router#show RAM
A13:
The correct answer is D. show RAM is not a Cisco IOS command.
Answers A, B, and C are incorrect because they are Cisco commands.
14.
Which of the following can be used to permit or deny traffic with IP
standard access lists? (Choose the two best answers.)
A. Source IP address
B. A range of source IP addresses
C. Destination IP address
D. A range of destination IP addresses
A14:
The correct answers are A and B. IP standard access lists allow IP
traffic to be filtered based on source IP addresses; they also allow both
individual IP addresses and a range of IP addresses to be specified.
Answers C and D are incorrect because IP standard access lists do not
filter traffic based on individual IP addresses or a range of destination IP
addresses.
15.
Which of the following commands will apply an IP extended access list
to an interface?
A. ip access-group 204 in
B. ip access group 110
C. ip access-group 115 out
D. ip access-group 95 out
E. ipx access-group 805 in
A15:
The correct answer is C. The command in answer C identifies an IP
extended access list by the correct numeric range (100 through 199) for
IP extended access lists. Answer A is incorrect because it uses the
access list number 204, which is reserved for protocol type access lists.
Answer B is incorrect because the command is not in the correct
format; it should be ip access-group, not ip access group. In addition,
the command should specify whether the access group is being applied
to inbound or outbound packets with the "in" or "out" identifier. Answer
D is incorrect because it identifies an IP standard access list (access list
number 95), not an IP extended access list. Answer E is incorrect
because it identifies an IPX standard access list, not an IP extended
access list.
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16.
What is the valid range for an IP extended access list?
A. 1 through 99
B. 100 through 199
C. 800 through 899
D. 900 through 999
A16:
The correct answer is B. IP extended access lists are identified by the
numeric range of 100 through 199. Answer A is incorrect because the
numeric range of 0 through 99 identifies IP standard access lists.
Answer C is incorrect because the numeric range of 800 through 899
identifies IPX standard access lists. Answer D is incorrect because the
numeric range of 900 through 999 identifies IPX extended access lists.
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PART THREE:
SAMPLE EXAMS
These chapters serve a special purpose: They are designed to test whether you
are ready to take your CCNA exams.:
Chapter 11 deals with exam 640-821
Chapter 12 deals with exam 640-811
Chapter 13 deals with exam 640-801.
Each exam is followed by an answer key and brief explanation of correct
answers along with an explanation for why the other answers are incorrect.
Reading these chapters prior to other chapters is like reading the climax of a
story and then going back to find out how the story arrived at that ending. Of
course, you don't want to spoil the excitement, do you?
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How to Take the Practice Exams.
Like the real Cisco exams, each exam in this book consists of between 55 and
65 questions. Also like the Cisco exams, you should complete each test within 90
minutes. The number of questions and the time duration in the actual exam may
vary but should be close to this number.
Which practice exam you take depends on which of the CCNA exams you are
preparing for. Once you have read the material presented in the chapters, you
should take the practice exam that corresponds to the CCNA exam you are
looking to pass. After the exam is complete, evaluate yourself using the answer
key at the end of the chapter. When you evaluate yourself, note the questions
you answered incorrectly, identify the corresponding chapters in the book, and
then read and understand that material before taking the exam again.
The 640-801 exam is in some ways a combination of both the 640-811 and 640821 exams. Students preparing to take one set of exams can gain something
from taking practice exams for the other set of exams. Be aware, though, that not
all of the same exam objectives are covered on both sets of exams.
Exam Taking Tips.
Take these exams under your own circumstances, but I strongly suggest that
when you take them, you treat them just as you would treat the actual exam at
the test center. Use the following tips to get maximum benefit from the exams:
 Before you start, create a quiet, secluded environment where you are not
disturbed for the duration of the practice exam.
 Provide yourself a few empty sheets of paper before you start. Use some
of these sheets to write your answers, and use the others to organize your
thoughts. At the end of the exam, use your answer sheet to evaluate your
exam with the help of the answer key that follows the sample exam.
 Don't use any reference material during the exam.
 Some of the questions may be vague and require you to make deductions
to come up with the best possible answer from the possibilities given.
Others may be verbose, requiring you to read and process a lot of
information before you reach the actual question.
 Always read the question carefully. Sometimes a question can seem to be
asking one thing when in fact it is asking something entirely different.
 As you progress, keep track of the elapsed time and make sure that you'll
be able to answer all the questions in the given time limit.
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Chapter 11. Sample Exam 640-821
1.
Which of the following commands can be issued from the command
line on a router to directly check the connectivity between one router
and another on a TCP/IP network? (Select all that apply.)
A. ping
B. enable
C. trace
D. show ip arp
2.
Traffic is not passing between a router at the core of your network
and the border router connected to your leased line to the ISP. Your
network has several routers. You know the path that packets should
take from the core router to the border router. You wish to determine
which of the routers may have failed by attempting to view the path
that packets take from the core router to the border router. Which of
the following IOS commands, used once, will enable you to do this
assuming that you are logged in to the console of the core router and
know the IP address of the border router?
A. path
B. trace
C. show route
D. ping
3.
Which of the following are methods via which configuration tasks can
be performed on Cisco routers? (Select all that apply.)
A. Direct console connection
B. Telnet
C. SSH
D. Terminal server
4.
You wish to configure a Cisco router via a telnet session. Which of
the following TCP ports will the router accept a telnet connection on?
A. Console port
B. Port 21
C. Port 23
D. Port 25
E. Port 80
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5.
Which of the following Cisco IOS 12.x commands will display the IP
address information of all of the interfaces on a Cisco router? (Select
one.)
A. show ip interface brief
B. display all ip
C. list ip interface all
D. show hosts
6.
Which of the following Cisco IOS 12.x commands will not display IP
address information for interface e0? (Select all that apply.)
A. show ip interface brief
B. show interface e0
C. show ip interface e0
D. show ip arp
E. show ip interface e1
7.
You are connecting to a Cisco router via the console port from a
laptop computer, attempting to diagnose a problem with the router's
configuration. Which of the following COM settings should you use
on the laptop to correctly connect to the router via the console port?
A. 9600bps, 8 data bits, no parity, 1 stop bit, no flow control
B. 9600bps, 7 data bits, parity, 1 stop bit, no flow control
C. 9600bps, 8 data bits, parity, 1 stop bit, flow control
D. 9600bps, 7 data bits, no parity, 1 stop bit, flow control
E. 9600bps, 8 data bits, no parity, 1 stop bit, flow control
8.
You are on site trying to diagnose a problem with a Cisco 2500
series router. To perform this diagnosis, you need to get access to
the router. To do this, you will be using a cable to connect to the
Cisco router's console port from your laptop via a 9-pin com port.
Which of the following cables should you use to make this
connection? (Select two.)
A. RJ-45 to RJ-45 rollover cable
B. DB-25 to DB-9 Adapter
C. DB-25 to DB-25 rollover cable
D. RJ-45 to DB-9 Adapter
9.
You are considering upgrading the version of IOS that runs on the
routers in your organization. You have stored the newer version of
IOS on a TFTP server. Which of the following IOS commands can be
used to copy an IOS image from a TFTP server to the flash memory
on a router?
A. copy flash tftp
B. download ios image
C. copy image flash
D. copy tftp flash
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10.
You are interested in backing up a router's running configuration to
your TFTP server. This is done so that if alterations are made in the
future, the current configuration can quickly be restored. Which of the
following IOS commands will allow you to do this?
A. copy tftp flash
B. copy start tftp
C. copy running-config tftp
D. copy tftp running-config
11.
You are in the process of assigning hostnames to routers on your
network. You have decided that each router on your network requires
a different name so that it is obvious to whomever is remotely
configuring the router which router they are working on. Which of the
following commands will set a router's hostname to ROOSKA?
A. set name ROOSKA
B. configure name ROOKSA
C. set mode banner ROOSKA
D. configure banner ROOSKA
E. hostname ROOSKA
12.
Which of the following IOS commands will set the message for all
terminal connections to the router to "Welcome to Router Rooslan"?
A. set banner #Welcome to Router Rooslan#
B. banner motd #Welcome to Router Rooslan#
C. set motd #Welcome to Router Rooslan#
D. configure motd #Welcome to Router Rooslan#
E. configure banner #Welcome to Router Rooslan#
13.
You have 10 routers in your network. You believe that one of these
routers has failed, but you are not sure which one. You know the IP
addresses of interfaces on each of the routers. You are logged in to
the console of one of these 10 routers and have verified that this
router is fully functional. Which of the following IOS commands can
you use to check the network connectivity of other routers in the
network? (Select all that apply.)
A. show cdp neighbors
B. ping
C. pathping
D. display network
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14.
Rooslan is configuring a new network and wishes to assign the final
IP host address at the end of the IP address range 10.10.224.0 /20
to interface e0 on a Cisco 2500 series router. This should be an
addressable host address and only one number below the network
broadcast address. Which of the following commands can Rooslan
use to do this assuming that he is at the interface configuration
prompt for e0?
A. Router(config-if)#ip address 10.10.224.1 255.255.255.0
B. Router(config-if)#ip address 10.10.224.1 255.255.248.0
C. Router(config-if)#ip address 10.10.239.254 255.255.248.0
D. Router(config-if)#ip address 10.10.239.254 255.255.240.0
E. Router(config-if)#ip address 10.10.255.254 255.255.240.0
15.
You are configuring a router that will separate the 192.168.20.224
/29 network connected to interface e0 from the 192.168.20.192 /28
network on interface s1. Which of the following, from the interface
configuration prompt for e0, will configure the interface with a correct
host address? (Select all that apply.)
A. Router(config-if)#ip address 192.168.20.193 255.255.255.240
B. Router(config-if)#ip address 192.168.20.193 255.255.255.248
C. Router(config-if)#ip address 192.168.20.225 255.255.255.240
D. Router(config-if)#ip address 192.168.20.225 255.255.255.248
E. Router(config-if)#ip address 192.168.20.231 255.255.255.248
F. Router(config-if)#ip address 192.168.20.129 255.255.255.240
16.
You are investigating using VLANs to improve the utilization of
bandwidth on your company's network. Which of the following
hardware devices is used on a local area network to directly provide
VLAN functionality?
A. Router
B. Switch
C. Bridge
D. Hub
17.
Which of the following operating systems can be installed on a Cisco
router, enabling it to be configured to route packets, implement
access lists, and provide routing protocol updates to other routers on
the network?
A. Linux
B. IOS
C. FreeBSD
D. Windows Server 2003
E. Solaris
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18.
You are attempting to determine the nature of devices connected to
your Cisco router while logged in to IOS via the console cable. All
devices on your network are Cisco products. Which of the following
commands will inform you if the Cisco products present on the
network are routers, switches, or repeaters?
A. list network devices
B. ping devices
C. identify connections
D. show cdp neighbors
E. trace neighbors
19.
You are connected to a central router that has several other routers
connected to it. You wish to generate a list of all of the IOS versions
in use on those routers. Which of the following IOS commands can
you use from the console to generate this information?
A. show cdp neighbor detail
B. show cdp neighbor
C. audit IOS
D. show cdp audit
20.
Which of the following commands will shut down an interface,
suspending connectivity between the router and the network
connected to that interface as well as informing routing protocols that
this interface is unavailable?
A. Router(config-if)# shutdown
B. Router(config-if)# stop
C. Router(config-if)# halt
D. Router(config-if)# terminate
E. Router(config-if)# bootdown
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21.
You are the network administrator of a network that has five routers.
You have the following information:
Interface e0 on Router 1 connects to network 192.168.10.0 /28
Interface s1 on Router 1 has an IP address of 192.168.10.18
Interface s1 on Router 2 connects to network 192.168.10.48 /28
Interface s2 on Router 2 connects to network 192.168.10.64
Interface e0 on Router 2 has an IP address of 192.168.10.2
Interface e0 on Router 3 connects to network 192.168.10.16 /28
Interface s1 on Router 3 has an IP address of 192.168.10.33
Interface s1 on Router 4 has an IP address of 192.168.10.50
Interface e0 on Router 4 connects to network 192.168.10.32
Interface s2 on Router 4 connects to network 192.168.10.80
Interface s0 on Router 5 has an IP address of 192.168.10.66
Interface e0 on Router 5 has an IP address of 192.168.10.82
Which of the following commands can be issued while maintaining
connectivity between all of the routers?
A. On interface e0 on Router 1 issue the shutdown command. On
interface s1 on Router 3 issue the shutdown command.
B. On interface e0 on Router 1 issue the shutdown command. On
interface s1 on router 2 issue the shutdown command.
C. On interface e0 on Router 1 issue the shutdown command. On
interface e0 on Router 4 issue the shutdown command.
D. On interface e0 on Router 1 issue the shutdown command. On
interface e0 on Router 3 issue the shutdown command.
22.
Which of the following numbers are the same in decimal, binary, and
hexadecimal? (Perform the conversion without a calculator. Select all
that apply.)
A. Decimal: 255, Hexadecimal: FF, Binary: 11111111
B. Decimal: 254, Hexadecimal: FD, Binary: 11111110
C. Decimal: 252, Hexadecimal: FC, Binary: 11111101
D. Decimal: 248, Hexadecimal: F7, Binary: 11111000
E. Decimal: 240, Hexadecimal: F0, Binary: 11110000
F. Decimal: 224, Hexadecimal: E0, Binary: 11100000
23.
Which of the following IP addresses is correctly converted into
hexadecimal notation? (Perform the conversion without a calculator.
Select all that apply.)
A. 10.23.193.237 = 0A.17.C1.ED
B. 10.178.19.113 = 0A.B1.13.71
C. 10.42.164.211 = 0A.2B.A4.D3
D. 10.191.37.123 = 0A.BF.26.7B
E. 10.77.228.100 = 0A.4D.E4.64
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24.
Which of the following network devices configures the network so
that each individual host on the LAN is connected to its own
individual segment?
A. Router
B. Hub
C. Bridge
D. Repeater
E. Switch
25.
Which of the following statements about WANs and LANs are true?
(Select all that apply.)
A. Hosts on WANs are generally connected together via high speed
data links.
B. Hosts on LANs are generally connected together via high speed
data links.
C. Hosts on WANs share close geographic proximity to each other.
D. Hosts on LANs share close geographic proximity to each other.
E. Frame Relay is a technology likely to be used on a WAN.
F. Frame Relay is a technology likely to be used on a LAN.
26.
You are configuring a local area network in a star topology. Your
network will not need to send any traffic to remote networks. Which
of the following devices can form the core of a star topology where
there are more than 20 hosts? (Select two.)
A. Router
B. Switch
C. Hub
D. Bridge
E. Repeater
27.
Which of the following configuration settings does a host on a TCP/IP
network require in order to communicate with hosts on a remote
TCP/IP network? (Select all that apply.)
A. DNS server address.
B. DHCP server address.
C. IP address.
D. Subnet mask.
E. Default gateway address.
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28.
In which of the following situations would using CAT 5 UTP cable be
inappropriate on a LAN? (Select all that apply.)
A. In an environment where there is a large amount of
electromagnetic interference.
B. Where a host is 90 meters away from the nearest switch.
C. On Token Ring networks.
D. Where bandwidths of 1 gigabit per second need to be supported.
E. Where a host is 340 meters away from the nearest switch.
29.
Which of the following are properties of the 100BASE-FX standard?
(Select all that apply.)
A. Runs on Cat 6 UTP cable.
B. Runs on fiber-optic cable.
C. Able to run a maximum length of 200 meters from the switch
without signal enhancement.
D. Able to run a maximum length of 412 meters from the switch
without signal enhancement.
E. Runs at 100 Megabit per second.
F. Runs at 1 Gigabit per second.
30.
Which of the following technologies are likely to be used when
implementing a WAN but not likely to be used when implementing a
LAN? (Select all that apply.)
A. Leased line
B. ATM
C. Frame Relay
D. PPP
E. Gigabit Ethernet
31.
Which of the following technologies are likely to be used to connect
two networks in a LAN but not two networks in a WAN?
A. ISDN
B. Frame Relay
C. 100BASE-FX
D. 100BASE-TX
E. FDDI
F. Gigabit Ethernet
32.
Which of the following statements about IOS is false? (Select all that
apply.)
A. IOS is a graphic interface to configure a Cisco router.
B. IOS runs on almost all routers and most switches in the Cisco
range.
C. IOS images are stored in a router's flash memory.
D. IOS contains six exec modes: user mode, delineated mode,
privileged mode, extended mode, rescue mode, and control mode.
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33.
Which of the following are configuration modes that are available
once Privileged EXEC mode is entered when logged into the IOS CLI
via the console cable? (Select all that apply.)
A. Global configuration mode
B. Auxiliary configuration mode
C. Router configuration mode
D. UTP configuration mode
E. Line configuration mode
F. Interface configuration mode
34.
Which of the following statements describe roles of a router on a
WAN? (Select all that apply.)
A. A router determines which packets need to be forwarded to
remote networks via the WAN line and which packets should remain
on the local network.
B. A router can be configured to initiate a WAN connection when
traffic meeting specific criteria is encountered.
C. Routers on WANs are limited to using the TCP/IP protocol.
D. Routers are used to forward broadcast traffic to remote sites.
35.
Which of the following areas of router hardware is used to store the
running or active configuration?
A. RAM
B. ROM
C. Flash memory
D. NVRAM
36.
Which of the following areas of router hardware is used to store the
complete IOS images?
A. RAM
B. ROM
C. Flash memory
D. NVRAM
37.
Which of the following best represents the order in which a router
starts up?
A. Load Bootstrap Code; POST; Find and Load IOS Software; Find
and Load Configuration.
B. Load Bootstrap Code; Find and Load Configuration; POST; Find
and Load IOS Software.
C. POST; Load Bootstrap Code; Find and Load IOS Software; Find
and Load Configuration.
D. POST; Load Bootstrap Code; Find and Load Configuration; Find
and Load IOS Software.
E. POST; Find and Load IOS Software; Load Bootstrap Code; Find
and Load Configuration.
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38.
Understanding a router's bootup sequence is essential knowledge for
a CCNA candidate. Which of the following occurs immediately before
the startup-configuration is located in the router bootup sequence?
A. POST
B. Load Bootstrap Code
C. Find IOS Software
D. Load IOS Software
E. Load Configuration
39.
Which of the following are properties of the configuration register on
a modern Cisco 2500 series router? (Select all that apply.)
A. It is a 16-bit software register in the router and its value is set via
the config-register global config command.
B. It is a 16-bit hardware register in the router and its value is set via
jumpers.
C. It is a 64-bit software register in the router and its value is set via
the config-register global config command.
D. The configuration register instructs the router which of the three
operating systems: full function IOS, limited function IOS, or
ROMMON to load.
40.
The passwords for a Cisco 7200 series router have been lost. You
want to enter ROMMON mode so that you can reset the
configuration register, configuring the router to boot ignoring
NVRAM, allowing the console user to change the passwords. You
are connected to the router via a console cable and laptop running
HyperTerminal. You cycle the router's power. Which of the following
steps will bring you into ROMMON mode, allowing you to change the
configuration registers?
A. Press the <insert> key on the laptop's keyboard within 60 seconds
of the power of the router being cycled.
B. Press the <ctrl>, <alt>, and <delete> keys together on the laptop's
keyboard within 60 seconds of the power of the router being cycled.
C. Press the <F1> key on the laptop's keyboard within 60 seconds of
the power of the router being cycled.
D. Press the <ctrl> and <c> keys together on the laptop's keyboard
within 60 seconds of the power of the router being cycled.
E. Press the <break> key on the laptop's keyboard within 60 seconds
of the power of the router being cycled.
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41.
Which of the following statements about routing is correct?
A. Data is forwarded based on its Layer 2 address.
B. Data is forwarded based on its Layer 3 address.
C. Routing protocols are used to update routing tables.
D. Routed protocols are used to update routing tables.
E. All routing protocols broadcast route information every 60 seconds
to other routers.
42.
Which of the following protocols can be used by routers to determine
the best path to a remote network?
A. IGRP
B. EIGRP
C. FTP
D. HTTP
E. RIP
F. OSPF
43.
Oksana has been allocated a single /24 subnet, 172.16.1.0, to divide
between four different office locations. The first location has 112
addressable hosts, the second location has 50 addressable hosts,
the third location has 28 addressable hosts, and the fourth location
has 16 addressable hosts. Which of the following schemes will
properly divide the allocated subnet so that each location gets the
necessary number of host addresses?
A. SCHEME ONE
Location 1: 172.16.1.0 /25
Location 2: 172.16.1.128 /26
Location 3: 172.16.1.192 /26
Location 4: 172.16.1.224 /27
B. SCHEME TWO
Location 1: 172.16.1.0 /26
Location 2: 172.16.64.0 /26
Location 3: 172.16.128.0 /26
Location 4: 172.16.192.0 /26
C. SCHEME THREE
Location 1: 172.16.1.0 /25
Location 2: 172.16.128.0 /26
Location 3: 172.16.192.0 /27
Location 4: 172.16.224.0 /27
D. SCHEME FOUR
Location 1: 172.16.1.0 /25
Location 2: 172.16.1.128 /26
Location 3: 172.16.1.192 /27
Location 4: 172.16.1.224 /27
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44.
Rooslan needs to resubnet a single /24 subnet into 15 networks with
a maximum of 12 hosts per network. He wants to use a single
consistent subnet mask for all of these networks. He will be using
routers running the latest version of IOS. What will be the CIDR
notation for the subnet mask that he will use to achieve this?
A. /25
B. /26
C. /27
C. /28
E. /29
45.
You are trying to explain to your boss the difference between bridges
and routers, and the situations where each piece of equipment is
appropriate. Which of the following statements best summarize these
differences?
A. Bridges segment a network into separate collision domains while
forwarding broadcast traffic; routers divide networks into different
broadcast domains.
B. Bridges divide networks into different broadcast domains. Routers
segment a network into separate collision domains while forwarding
broadcast traffic.
C. Routers shift traffic at Layer 3 or the OSI model; bridges shift
traffic at Layer 2 of the OSI model.
D. Routers shift traffic at Layer 2 or the OSI model; Bridges shift
traffic at Layer 3 of the OSI model.
46.
A particular device on the network exhibits the following properties.
This device generally has two interfaces, though in some cases can
have more. Unicast frames are forwarded to an interface based on a
table that remembers which MAC address is connected to each
interface. This table is generated by noting the source MAC address
of each frame that enters the device through a particular interface.
This device forwards broadcast and multicast frames to all interfaces.
Which of the following devices fits this description?
A. Router
B. Bridge
C. Hub
D. Repeater
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47.
You have a subnet of 100 hosts on a LAN. All of these hosts are
connected to one of two 60-port hubs, each hub connecting 50 of the
hosts. The two hubs are connected together directly. Taking which of
the following actions will half the size of the collision domain without
re-subnetting the network?
A. Removing the two 60-port hubs and replacing them with two 60port switches.
B. Placing a router between the two hubs.
C. Placing a bridge between the two hubs.
D. Placing a repeater between the two hubs.
48.
You have 120 hosts on a LAN that is increasingly becoming bogged
down with broadcast traffic. The LAN is configured with four
interconnected 50-port hubs, each with 30 hosts connected. Which of
the following methods could you use to reduce the amount of
congestion associated with broadcast traffic?
A. Changing the four hubs to four switches.
B. Placing bridges between each hub-to-hub connection.
C. Connecting each of the four hubs to a switch instead of to each
other and allow the switch to mediate traffic.
D. Re-subnet the network into two networks. Place a router in the
middle. Connect two hubs to one network and two hubs to the other.
49.
A switch has been installed on a LAN where a small, but significant
proportion of frames that contain errors are being transmitted. Rather
than have these frames be forwarded by the switch, it has been
decided that all frames with errors should be dropped by the switch
entirely. Which of the following switching methods would allow this to
occur?
A. Store and forward
B. Fragment free
C. Cut through
D. Hybrid
50.
You are installing a switch on a LAN where the absolute minimum of
latency between a packet entering and leaving the switch is required.
Error correction is not an important consideration. Which of the
following switching methods would best suit the requirement?
A. Store and Forward
B. Fragment Free
C. Cut Through
D. Hybrid
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51.
A segment of ethernet on your network uses CSMA/CD. Which of the
following statements about what occurs next, when a collision is
detected, is true?
A. The sending host randomizes a timer and waits until that timer
expires before attempting to send again.
B. The sending host sends again after a predetermined period.
C. The sending host listens until the segment has no traffic and then
retransmits.
D. The sending host analyses the collision frame and retransmits
immediately if a broadcast frame is detected.
E. The sending host analyses the collision frame and retransmits
immediately if a multicast frame is detected.
52.
When CSMA/CD is in use on an Ethernet network and a host wishes
to initiate a unicast transmission to another host, which of the
following steps occurs first?
A. The primary host checks the segment to determine if it is currently
hosting traffic.
B. The primary host initiates a transmission that switches the network
into a hold state.
C. The primary host requests a token from the destination host.
D. The primary host receives a token from the segment.
53.
Host A has an IP address of 10.10.20.55. Host B has an IP address
of 10.10.20.60. Both are on the 10.10.20.0 /24 network. Host A has
information that it needs to transfer to Host B. Host A does not have
the MAC address of Host B, but does know Host B's IP address.
Which of the following protocols will Host A use to determine Host
B's MAC address?
A. RIPv2
B. IGRP
C. OSPF
D. ARP
E. EIGRP
54.
Which of the following ICMP message names corresponds to the
correct description of the message type?
A. Destination Unreachable: Source informed that there is a problem
delivering the packet.
B. Time Exceeded: Packet discarded after the amount of time it
takes for the packet to be delivered exceeds a specific value.
C. Source Quench: The ping command uses a source quench to
verify connectivity between two hosts.
D. Redirect: Router informs sender that a better route exists.
E. Echo: The source is sending data too fast and a request is sent to
slow the rate of transmission.
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55.
Which of the following WAN services uses packet switching? (Select
all that apply.)
A. HDLC
B. LAPB
C. Frame Relay
D. ATM
E. X.25
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Answer Key 640-821
1. A and C
2. B
3. A, B, and C
4. C
5. A
6. D and E
7. A
8. A and D
9. D
10. C
11. E
12. B
13. B and C
14. D
15. D and E
16. B
17. B
18. D
19. A
20. A
21. B
22. A, E, and F
23. A and E
24. E
25. B, D, and E
26. B and C
27. C, D, and E
28. A, D, and E
29. B, D, and E
30. A, C, and D
31. C, D, E, and F
32. A and D
33. A, C, E, and F
34. A and B
35. A
36. C
37. C
38. D
39. A and D
40. E
41. B and C
42. A, B, E, and F
43. D
44. D
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45. A and D
46. B
47. C
48. D
49. A
50. C
51. A
52. A
53. D
54. A, B, and D
55. C, D, and E
1.
Answers A and C are correct. Ping and TRace are used to check
connectivity between two routers. Ping sends ICMP messages to verify
connectivity. trace sends UDP packets to verify the current route to a
host. Answer B is incorrect because the enable command is used to
enter the enable mode. Answer D is incorrect because the show ip arp
command is used to display the IP ARP cache.
2.
Answer B is correct. trace will display as much of the path as is
available. Answer A is incorrect because the path command is not an
IOS command. Answer C is incorrect because the show route
command will not be useful in diagnosing this fault. Answer D is
incorrect; although ping could be used by attempting to contact each
router in the known path, the question specifies which command can be
used once to make this determination.
3.
Answers A, B, and C are correct. Direct console connection via a cable,
connecting via the network using the Telnet protocol, or connecting via
a terminal server (a terminal server is an especially configured router
with multiple asynchronous ports that are connected to the console
ports of other routers on the network) can be used to perform
configuration tasks on Cisco routers. Answer D is incorrect because
SSH, an encrypted and secure terminal protocol similar to telnet, is not
supported natively by IOS at this time and cannot be used to perform
configuration tasks.
4.
Answer C is correct. Answer C lists Port 23, which is the Telnet TCP/IP
port that routers accept network connections from. Routers can be
configured via the network using telnet. Answer A is incorrect because
the console port is used for a direct cable uplink to the router, not a
connection via the network. The console port is a physical port on the
router, Port 23, a TCP/IP port is a logical port. Answers B, D, and E are
incorrect because these TCP/IP ports support other protocols rather
than Telnet.
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5.
Answer A is correct. The show ip interface brief command will print out
a brief summary of each interface's IP addressing information. Answers
B and C are not valid Cisco IOS commands. Answer D is incorrect
because the show hosts command will only display host names and
corresponding IP addresses. The show hosts command will display
nothing about which router interface uses which IP.
6.
Answers D and E are correct. The trick with this question is that it asks
which will not display the IP address information for interface e0 rather
than which commands will. The false answers (correct in this case) are
show ip arp and show ip interface e1, both of which show the arp table
and the ip information for interface e1 rather than e0. Answer A is
incorrect because show ip interface brief will display the IP address
information for all interfaces on a router, of which e0 is one. Answers B
and C are incorrect because the show interface e0 command and show
ip interface e0 command will display this information.
7.
Answer A is correct. The configuration of programs like HyperTerminal
or a terminal emulator on Linux require that the console connection be
configured with the settings 9600bps, 8 data bits, no parity, 1 stop bit,
and no flow control. Answers B, C, D, and E are incorrect because they
do not include the required settings.
8.
Answers A and D are correct. The console port on Cisco routers uses
an RJ-45 connection. A rollover cable is required to connect to a laptop.
To connect to the 9-pin com port you will need an RJ-45 to DB-9
Adapter. Answer B is incorrect because a DB-9 adapter is not required.
Answer C is incorrect because DB-25 will not connect to the com port
and a DB-25 is not required.
9.
Answer D is correct. Copy tftp flash will initiate the process of copying
an IOS file from a TFTP server to the router's flash memory. Other
information will need to be specified such as the image name, the
address of the TFTP server, and whether or not you wish to erase other
images stored in the flash memory. Answer A is incorrect because it
attempts to copy data in flash memory to a TFTP server. Answers B
and C are also incorrect as neither command can be used to copy an
IOS image from a TFTP server.
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10.
Answer C is incorrect. Copy running-config tftp will upload a copy of the
running configuration to the TFTP server. Answer D is incorrect
because it will download a copy of a configuration into the runningconfiguration. Answer A is incorrect because it will allow information,
generally an IOS image, to be copied from the TFTP server to flash
memory. Answer B is incorrect because it will copy the startup config to
the TFTP server rather than the running-config. Although the startup
and running configs could possibly be the same, this should not be
assumed.
11.
Answer E is correct. The hostname command will allow the router's
hostname to be set. In this case, hostname ROOSKA will allow the
router's hostname to be set to ROOSKA. Answers A, B, C, and D are
incorrect. These are invalid IOS commands.
12.
Answer B is correct. The banner motd #BANNER TEXT# command
provides the correct IOS command to set the message for incoming
terminal connection clients. Answers A, C, and D are incorrect. The
commands are syntactically incorrect.
13.
Answers B and C are correct. Both the ping and the pathping
commands can be used to check connectivity between two hosts on a
network. Answer A is incorrect, although the show cdp neighbors
command will display routers directly connected to the router from
which the command is issued, it will not show routers several hops
away from that router. Answer D is incorrect, Display network does not
exist as a command in IOS.
14.
Answer D is correct as it is within the specified address range and uses
the correct subnet mask. The first part in solving this problem is
translating the CIDR notation of /20 into decimal quad notation. /20 is
equal to 255.255.240.0. This eliminates answers A, B, and C. The next
step is to calculate the network range: 10.10.224.0 has a range of
10.10.224.1 through to 10.10.239.255. 10.10.239.255 is the broadcast
address of that network which leaves 10.10.239.254 as the last
addressable host address. Answer E is incorrect because it is an IP
address outside the network range in question.
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15.
Answers D and E are correct. They both have the correct subnet mask
and have IP addresses which lie within the specified address range
(192.168.20.225 through to 192.168.20.231). Interface e0 is connected
to network 192.168.20.224 /29. Calculating the range of this network
forms the bulk of solving this question. CIDR (Classless Inter Domain
Routing) notation /29 translates to 255.255.255.248 in decimal quad.
This means that answers that have an alternative subnet mask listed to
255.255.255.248 are incorrect. Answer A is incorrect because it has the
subnet mask 255.255.255.240 and hence is incorrect. Answer C is
incorrect because it has the subnet mask 255.255.255.240 and hence
is incorrect. Answer F is incorrect because it has the subnet mask
255.255.255.240 and hence is incorrect.
16.
Answer B is correct. Of the devices listed, only switches can be used on
the local area network to directly provide VLAN functionality. Answer A
is incorrect because routers cannot be used to provide VLAN
functionality directly. Answer B is incorrect because routers cannot be
used to provide VLAN functionality directly. Answer C is incorrect as
routers cannot be used to provide VLAN functionality directly.
17.
Answer B is correct. Only IOS, which was originally based on a variant
of Unix, runs on Cisco routers. Answer A is incorrect, Linux will not run
on a Cisco router. Answer C is incorrect, FreeBSD will not run on a
Cisco router. Answer D is incorrect, Windows Server 2003 will not run
on a Cisco router. Answer E is incorrect, Solaris will not run on a Cisco
router.
18.
Answer D is correct. The show cdp neighbors command will not only list
the devices that neighbor the router, but, assuming that the devices
neighboring the router also use CDP (Cisco Discovery Protocol), which
is default for Cisco devices, it will also list whether or not the devices
are routers, switches, or repeaters. Answer A is incorrect because it
lists network devices and will not display this information. Answer B is
incorrect because ping devices will not list this information. Answer C is
incorrect because it identifies connections and will not list this
information. Answer E is incorrect because it lists trace neighbors and
will not list this information.
19.
Answer A is correct. The show cdp neighbor detail command will
provide an in-depth summary of the details of neighboring Cisco
devices. This information includes the version of IOS that the
neighboring router is running. Answer B is incorrect. Although show cdp
neighbor does display information about neighboring Cisco devices, it
does not include IOS version in its output. The other commands C and
D are not valid in IOS.
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20.
Answer A is correct. The shutdown command, issued from the interface
configuration mode, will shut down an interface, suspending
connectivity and informing routing protocols that this particular interface
is now down. Answers B, C, D, and E are incorrect because they will
not shut down an interface.
21.
Answer B is correct. This question is complex and may require that you
draw a diagram to resolve it. Only one set of shutdown commands, e0
on Router 1 and s1 on Router 2, can be implemented while retaining
connectivity between all routers. This option is presented in answer B.
This question involves working out where the redundant links exist in
this network. Three paths exist between routers 2 and 4. A direct path
from 2 via interface s1, a two-hop path via router 5, and a three-hop
path via router 1 and 3. As the first connection broken in every answer
is the one between router 1 and 2, a route between 2 and 4 can be
broken while maintaining connectivity to all routers. Answer A is
incorrect because it will break connectivity between routers, as no
redundant link exists between these interfaces. Answer C is incorrect
because it will break connectivity between routers, as no redundant link
exists between these interfaces. Answer D is incorrect because it will
break connectivity between routers, as no redundant link exists
between these interfaces.
22.
Answer A, E, and F are correct. A Cisco candidate should be able to
convert freely between decimal, binary, and hexadecimal. Answer A
maps correctly with 255 = FF = 11111111. Answer E maps correctly
with 240 = F0 = 11110000. Answer F maps correctly with 224 = E0 =
11100000. Answer B is incorrect. The mapping should be: 254 = FE =
11111110. Answer C is incorrect, the mapping should be: 252 = FC =
11111100. Answer D is incorrect, the mapping should be: 248 = F8 =
11111000.
23.
Answer A and E are correct. 10.23.193.237 maps
10.77.228.100 maps to 0A.4D.E4.64. Answer
10.178.19.113 maps to 0A.B2.13.71. Answer
10.42.164.211 maps to 0A.2A.A4.D3. Answer
10.191.37.123 maps to 0A.BF.25.7B.
24.
Answer E is correct. A switch is used to configure the network so that
each individual host on the LAN is connected to its own individual
segment. Answer A is incorrect as routers do not segment a network;
they are used to divide logical networks. Answer C is incorrect as
bridges do segment networks; however, hosts still share a segment
when a bridge is implemented. Answer D is incorrect as repeaters
forward all data transmitted to them and do not segment the network.
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to 0A.17.C1.ED and
B is incorrect as
C is incorrect as
D is incorrect as
25.
Answers B, D, and E are correct. Hosts on LANs are usually connected
via high-speed data links. LANs are often in close geographic proximity
to one another, whereas WANs can stretch across a continent. Frame
Relay is used for WAN connections. Answer A is incorrect because
hosts on WANs are linked at speeds much lower than LAN speeds.
Answer C is incorrect because WANs are geographically diverse, the
next suburb or the next town rather than the next room or building.
26.
Answers B and C are correct. Star networks have a central point to
which each host on the network is connected. The two devices that can
form the core of star topologies are the hub (B) and the switch (c).
Routers are used to send traffic to remote networks. The question
states that sending remote traffic is not required. Bridges (D) are
generally used to reduce the size of collision domains and do not form
the core of star topology LANs. Repeaters (E) are used to lengthen the
distance between the switch or hub and the host and do not form the
core of star topology LANs.
27.
Answers C, D, and E are correct. To communicate with hosts on a
remote TCP/IP network, a host requires an IP address, a subnet mask,
and a default gateway address. Answer A is incorrect, because though
a DNS server can help in resolving FQDN addresses to IP addresses, it
is not required for communication to occur between a host and another
host on a remote subnet. Answer B is incorrect. Although DHCP
servers are useful in providing address information, this can be
configured manually.
28.
Answers A, D, and E are correct. CAT 5 UTP does not handle
electromagnetic interference well and hence is an inappropriate
technology to use in that situation. It supports bandwidths up to 100
megabits per second. Without using a repeater it reaches 100 meters.
Depending on which repeaters are used, this can be extended to near
300 meters, not 340. Answers B and C are incorrect. Answer B is
incorrect, as CAT 5 UTP can be used without problem on a host only 90
meters from the switch. Answer C is incorrect, as CAT 5 UTP can be
used on Token Ring networks.
29.
Answers B, D, and E are correct. 100BASE-FX runs on fiber-optic
cable. It is able to run a length of 412 meters before needing a repeater
and it runs at 100 megabits per second. Answer A is incorrect,
100BASE-FX does not run on UTP. Answer C is incorrect as it will run a
maximum of 412, not 200 meters without needing signal enhancement.
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30.
Answers A, C, and D are correct. Leased lines, Frame Relay, and PPP
are WAN technologies. Answer B is incorrect because ATM is limited to
LAN distances and cannot provide connectivity over WAN distances
(such as between two cities). Answer E is incorrect because Gigabit
Ethernet suffers from distance limitations as well.
31.
Answers C, D, E, and F are correct. LAN connections are characterized
by their proximity to one another. Connected LANs might be in adjacent
buildings or on different floors of an office tower. WAN networks often
span states if not continents. WAN connections generally operate at
lower speed than LAN connections. 100BASE-FX has a maximum
range of 412 meters. 100BASE-TX has a maximum range of 100
meters. FDDI has a better range, but cannot span the hundreds of
kilometers that some WAN links must. Gigabit Ethernet also provides
high bandwidth but is limited in its range. Answers A and B are incorrect
because ISDN and frame relay connections can be used not only
across the city but across the continent and are the most common types
of WAN connections.
32.
Answers A and D are correct. This question asks which statements are
false. Answer A is correct because its statement is false: IOS is not a
graphic interface, it is a text-only interface. Answer D is correct as its
statement is false: there are only two modes, privileged and user exec.
Answer B is true hence is an incorrect answer. IOS does run on almost
all of Cisco's routers and most of Cisco's switches. Answer C is true
hence is an incorrect answer. IOS images are stored in a router's flash
memory. Although such a "list the false answer" question is unlikely to
occur on the exam, it should remind you to read a question carefully
rather than to briefly glance at it assuming you have fully grasped its
scope.
33.
Answers A, C, E, and F are correct. There are four configuration modes
available once the Privileged EXEC mode is entered. These four modes
are Global, Router, Line, and Interface configuration. Answer B is
incorrect, as Auxiliary configuration mode does not exist, even though
connections can be initiated through the auxiliary port. Answer D is
incorrect, as UTP configuration modes do not exist, even though there
are UTP ports. Certain tasks, such as assigning an IP address to an
interface, must be done within particular configuration modes.
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34.
Answers A and B are correct. Routers forward packets based on the
network address contained within the destination header. This means
that routers will determine which packets need to be forwarded to
remote networks via the WAN line. Routers can also be configured to
initiate WAN connections when traffic meeting specific criteria is
encountered. Answer C is incorrect, as routers on WANs are not limited
to using TCP/IP. Routers using leased or dial-up lines can transmit
other protocols such as IPX. Answer D is incorrect, as routers do not
forward broadcast traffic to remote sites.
35.
Answer A is correct as RAM stores the running/active configuration.
Answer B is incorrect, as ROM stores the bootable IOS image that is
used until the router locates the full IOS image. Answer C is incorrect,
as flash memory stores fully functional IOS images. Answer D is
incorrect, as NVRAM stores the initial/startup config file.
36.
Answer C is correct; Flash Memory stores fully functional IOS images.
Answer A is incorrect, as RAM stores the running/active configuration.
Answer B is incorrect, as ROM stores the bootable IOS image that is
used until the router locates the full IOS image. Answer D is incorrect,
as NVRAM stores the initial/startup config file.
37.
Answer C is correct. The sequence for router bootup is
POST (power on self test)
Load bootstrap code
Find and load IOS software
Find and load configuration
Begin operation
Answer A is incorrect, as it presents the sequence out of order, placing
POST after loading bootstrap code. Answer B is incorrect for the same
reason. Answer D is incorrect, as the configuration is loaded before the
IOS software. Answer E is incorrect, as IOS software is loaded before
bootstrap code.
38.
Answer D is correct. The IOS software is loaded before the startupconfiguration file is located. Answer A is incorrect, as POST occurs
before anything else at the start of the sequence. Answer B is incorrect,
as loading the bootstrap code occurs well before the startupconfiguration is located. Answer C is incorrect, as this occurs two steps
before, not immediately before the startup-configuration is located.
Answer E is incorrect, as the loading of the configuration is performed
after the startup-configuration is located.
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39.
Answers A and D are correct. The configuration register is a 16-bit
software register. It can be set via the config-register global
configuration command. Some older routers did use jumpers for the
configuration register. The configuration register is used to inform the
router which of the three operating systems—full function IOS, limited
function IOS, or ROMMON—to load. Limited function IOS is used when
images in flash memory have become corrupted and connectivity is
required to retrieve a new uncorrupted image from a TFTP server.
ROMMON is used for debugging and password recovery. Answer B is
incorrect, as the register is in software not in hardware. Answer C is
incorrect, as the register is 16 rather than 64 bit.
40.
Answer E is correct. The first step in resetting a router's password is to
get the router to boot into ROMMON mode so the configuration register
can be reconfigured to bypass NVRAM when booting. This is done by
holding down the <break> key on the device connected to the console
within 60 seconds of the router powering up. Additional steps for
completing this task can be found on Cisco's Web site:
http://www.cisco.com. Answer A is incorrect, as this method will not
work. Answer B is incorrect, as this method will not work. Answer C is
incorrect, as this method will not work. Answer D is incorrect, as this
method will not work.
41.
Answers B and C are correct. Answer B is correct because routing uses
Layer 3 logical address information to forward data. Answer C is
correct, as routing protocols update routing tables. Answer A is
incorrect, as switches use Layer 2 information to forward data. Answer
D is incorrect as routing rather than routed protocols update routing
tables. Answer E is incorrect as only some routing protocols broadcast
route information every 60 seconds.
42.
Answers A, B, E, and F are correct. IGRP (a), EIGRP (b), RIP (e), and
OSPF (f) are all routing protocols. Routing protocols find paths through
networks, generating routing tables that are used to forward packets
expeditiously to their destination. Answers C and D are incorrect. FTP is
used for file transfer and HTTP is used for the transfer of Web pages.
Both are considered routed protocols.
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43.
Answer D is correct. Scheme four allocates four subnets. The first,
172.16.1.0 /25, will allow 126 hosts on the network, meeting the
requirement of 112. The second, 172.16.1.128 /26 will allow 62 hosts
on the network, meeting the requirement of 50. Networks 172.16.1.192
and 172.16.1.224 will both allow 30 hosts on the network, meeting the
requirements of 28 and 16 addressable hosts respectively. Answer A is
incorrect as Scheme 1 contains incorrect subnetting information.
Answer B is incorrect as Scheme 2 doesn't meet the requirements listed
in the question. Answer C is incorrect as scheme 3 deals with subnets
other than the original /24 allocated.
44.
Answer D is correct. A /28 subnetting will provide 16 networks that can
host a maximum of 14 hosts per network, meeting the requirement
listed in the question. Answer A is incorrect, as /25 network will have 2
networks with 126 hosts. Answer B is incorrect, as a /26 network will
have 4 networks of 62 hosts. Answer C is incorrect, as a /27 network
will have 8 networks with 30 hosts each. Answer E is incorrect, as a /29
network will have 32 networks with 6 hosts per network.
45.
Answers A and C are correct. Bridges segment a network into separate
collision domains while forwarding broadcast traffic. Routers do not
forward broadcast traffic and divide networks into different broadcast
domains. This means answer A is correct. Answer C is correct because
routers work at Layer 3 of the OSI model and bridges work at Layer 3 of
the OSI model. Answer B is incorrect because it is the opposite of
answer A and suggests that routers forward broadcast traffic. Answer D
is incorrect, as routers work at Layer 3 of the OSI model.
46.
Answer B is correct. Of the options presented, only a bridge has these
characteristics listed in the question. Answer A is incorrect, as routers
deal with packets (Layer 3) rather than frames (Layer 2). Answer C is
incorrect, as hubs forward all traffic and do not generate tables. Answer
D is incorrect, as bridges forward broadcast and multicast frames.
47.
Answer C is correct. Placing a bridge between the two hubs will reduce
the size of the collision domain by 50% as specified in the question.
Answer A is incorrect, as replacing the two hubs with switches will
reduce the size of the collision domain by far more than half. Answer B
is incorrect, as placing a router between the hubs will require resubnetting the network. Answer D is incorrect, as placing a repeater
between the two hubs will not change the size of the broadcast
domains.
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48.
Answer D is correct. Only by implementing a router will broadcast traffic
be reduced. Answer A is incorrect, as switches forward broadcast
traffic. Answer B is incorrect, as bridges do not filter broadcast traffic.
Answer C is incorrect, as switches do not forward broadcast traffic.
49.
Answer A is correct. Store and forward switching has each frame read
into a buffer and performs a CRC check on it. Any frame that fails the
CRC check is discarded. Answer B is incorrect because fragment free
checks the first 64 bytes of a frame, as statistical analysis has shown
that if a frame is corrupted, almost always the corruption will be evident
in the first 64 bytes. However, this is not true 100% of the time, hence
will not satisfy the question condition that all frames with errors should
be dropped. Answer C is incorrect, as cut-through switching only
checks the frame's destination address and performs no error correction
function. Answer D is incorrect, as hybrid is another name for fragment
free.
50.
Answer C is correct. Cut-through switching only checks the frame's
destination address and performs no error correction function. This
method has the lowest latency. Answer A is incorrect, as store-andforward switching has each frame read into a buffer and performs a
CRC check on it. Any frame that fails the CRC check is discarded. This
method has the highest latency. Latency increases with frame size.
Answer B is incorrect, as fragment free checks the first 64 bytes of a
frame as statistical analysis has shown that if a frame is corrupted,
almost always the corruption will be evident in the first 64 bytes. The
latency of the 64-byte check, although small, is higher than that
imposed by cut-through switching. Answer D is incorrect, as hybrid
switching is another name for fragment-free switching, which as
explained in answer B has more latency than cut-through switching.
51.
Answer A is correct. In the CSMA/CD routine on a segment of shared
ethernet, if a collision is detected, a random timer is set. Once that timer
expires, the process starts again with the host checking the network for
traffic and, if the network is clear, initiating transmission. Answer B is
incorrect, as the next step is waiting for a random amount of time rather
than a fixed amount. Answer C is incorrect because the next step is to
wait for a random amount of time, not to check the network. Answer D
is incorrect, as the next step is to wait a random amount of time, not to
analyze the frame. Answer E is incorrect, as the next step is to wait a
random amount of time, not to retransmit if a multicast frame is
detected.
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52.
Answer A is correct. When CSMA/CD is in use on Ethernet, the first
part of the process is that the host wishing to initiate a transmission
checks the network for any current traffic. Answer B is incorrect, as
ethernet networks cannot be placed into a hold state. Answers C and D
are incorrect, as Ethernet networks do not use tokens.
53.
Answer D is correct. ARP is the Address Resolution Protocol and is
used to determine MAC addresses for a given TCP/IP address. ARP is
used when one host wishes to determine the MAC address of another
host when it knows its IP address. Answer A is incorrect because RIPv2
is not used when one host wishes to determine the MAC address of
another host when it knows its IP address. Answer B is incorrect
because IGRP is not used when one host wishes to determine the MAC
address of another host when it knows its IP address. Answer C is
incorrect because OSPF is not used when one host wishes to
determine the MAC address of another host when it knows its IP
address. Answer E is incorrect because EIGRP is not used when one
host wishes to determine the MAC address of another host when it
knows its IP address.
54.
Answers A, B, and D are correct. Answer A provides the definition of
the ICMP Destination Unreachable Message, that there is a problem
delivering the packet. Answer B provides the definition of the Time
Exceeded message, that the packet has been discarded after the
amount of time it takes for a packet to be delivered. Answer C is
incorrect; Ping does not use a source quench to verify connectivity.
Answer D provides the correct definition of the Redirect message, that a
better route exits. Answer E is incorrect; Echo is not generated in
response to data being sent too fast.
55.
Answers C, D, and E are correct. Answer C, frame relay, is classified as
a packet-switching technology. Frame relay is sometimes called frame
switching, but it is common within Cisco nomenclature to refer to frame
relay as a packet-switching technology. Answer D, ATM, is classified as
a packet-switching technology. Answer E, X.25, is classified as a
packet-switching technology. Answer A, HDLC, is used on leased lines
rather than over a packet switched service. Answer B, LAPB, is used on
leased lines rather than over a packet-switched service.
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CHAPTER 12.
Sample Exam 640-811
1.
You have the following devices to use in constructing a simple LAN
on two separate floors of a building. The distance between each floor
is 6 meters.
1 2500 Series router.
10 Catalyst 2950 Switches (24 port).
2 Repeaters.
2 Bridges.
You have 200 desktop workstations and 4 servers. 90 workstations
and 2 servers will be located on the 5th floor of the building. 110
workstations and 2 servers will be located on the 7th floor of the
building. Because of the extensive traffic between the workstations
and the servers, you have decided to create a separate TCP/IP
subnet for each floor. Which of the following represents the best use
of equipment in designing a simple LAN, given the requirements?
A. Place 4 of the Catalyst 2950 switches in stacked configuration on
the fifth floor. Connect the 5th floor workstations and the servers to
this stack. Place the remaining 6 Catalyst 2960 switches in stacked
configuration on the 7th floor. Connect the 7th floor workstations to
this stack. Connect the 5th floor stack to one of the bridges. Connect
the 7th floor stack to the second bridge. Interconnect the Bridges via
the 2 repeaters.
B. Place 4 of the Catalyst 2950 switches in stacked configuration on
the 5th floor. Connect the 5th floor workstations and the servers to
this stack. Place the remaining 6 Catalyst 2950 switches in stacked
configuration on the 7th floor. Connect the 7th floor workstations to
this stack. Connect the 5th floor stack to the 2500 series router.
Connect the 7th floor stack to the 2500 series router. Configure
appropriate static routes.
C. Place 6 of the Catalyst 2950 switches in stacked configuration on
the 5th floor. Connect the 5th floor workstations and the servers to
this stack. Place the remaining 4 Catalyst 2950 switches in stacked
configuration on the 7th floor. Connect the 7th floor workstations to
this stack. Connect the 5th floor stack to the 2500 series router.
Connect the 7th floor stack to the 2500 series router. Configure
appropriate static routes.
D. Place 6 of the Catalyst 2950 switches in stacked configuration on
the 5th floor. Connect the 5th floor workstations and the servers to
this stack. Place the remaining 4 Catalyst 2950 switches in stacked
configuration on the 7th floor. Connect the 7th floor workstations to
this stack. Connect the 5th floor stack to the 7th floor stack via
repeaters.
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2.
Rooslan has been asked to help improve the responsiveness of the
LAN at his grandfather's architecture consultancy. At present there
are 15 hosts on the network. All of these hosts are connected to a
single 20 port 10Mbps hub. Copying files to and from the server, or
to other workstations, during normal business hours can take quite a
lot of time. Which of the following Cisco devices could Rooslan
implement to most improve the responsiveness of this network by
reducing congestion?
A. Replace the 10Mbps hub with a Cisco 2500 series router.
B. Replace the 10Mbps hub with a Cisco wireless bridge.
C. Replace the 10Mbps hub with a 100Mbps hub.
D. Replace the 10Mbps hub with a Cisco Catalyst 2950 10/100Mbps
switch.
3.
Your Web hosting firm has been allocated a class C IP network
address. You have four locations. The first in Phoenix, Arizona hosts
100 servers. The second one in Sydney, Australia hosts 50 servers.
The third one in Moscow, Russia hosts 20 servers, and the fourth in
Brasilia, Brazil hosts 18 servers. You are tasked with resubnetting
the class C IP address space, aware that all of your routers support
CIDR. Which of the following subnet masks should be applied to
each location?
A. Phoenix: 255.255.255.192, Sydney: 255.255.255.192, Moscow:
255.255.255.224, Brasilia 255.255.255.224.
B. Phoenix: 255.255.255.128, Sydney: 255.255.255.224, Moscow:
255.255.255.240, Brasilia 255.255.255.248.
C. Phoenix: 255.255.255.128, Sydney: 255.255.255.192, Moscow:
255.255.255.224, Brasilia 255.255.255.240.
D. Phoenix: 255.255.255.128, Sydney: 255.255.255.192, Moscow:
255.255.255.224, Brasilia 255.255.255.224.
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4.
You are designing an IP addressing scheme for a company that has
three branch offices located throughout the country. Each office can
be assigned IP addresses from the private address space, as all of
their Internet access is handled through proxy servers and none of
the hosts needs to be accessed from the public Internet. The first
office in Minneapolis requires a single subnet that will support 300
hosts. The second office in Melbourne requires a single subnet that
will support 120 hosts. The third office in Vancouver requires a single
subnet that will support 28 hosts. Which of the following private IP
addressing schemes will meet the needs of each of the offices?
(Select all that apply.)
A. Minneapolis: 192.168.1.0 /24
Melbourne: 192.168.2.0 /24
Vancouver: 192.168.3.0 /24
B. Minneapolis: 192.168.2.0 /23
Melbourne: 192.168.4.0 /24
Vancouver: 192.168.5.0 /24
C. Minneapolis: 192.168.1.0 /25
Melbourne: 192.168.2.0 /25
Vancouver: 192.168.3.0 /25
D. Minneapolis: 192.168.2.0 /23
Melbourne: 192.168.4.0 /25
Vancouver: 192.168.6.0 /26
5.
Rooslan is the network engineer for a university. There are three
campuses and several remote sites that are all a part of the
university network. Using the traceroute utility Rooslan determines
that the network diameter is up to 25 hops. Which of the following
routing protocols would not be able to map routes of this length?
(Choose all that apply.)
A. RIP
B. RIPv2
C. IGRP
D. EIGRP
E. OSPF
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6.
Oksana is the network engineer in a network that has routers from
multiple vendors. The majority of the routers on the network were
manufactured by Cisco systems, but there are routers from other
manufacturers that perform critical tasks and cannot be replaced at
this time. Which of the following routing protocols are not proprietary
to Cisco and hence are likely to be supported by non-Cisco vendors?
(Choose all that apply.)
A. RIPv2
B. OSPF
C. IGRP
D. EIGRP
7.
Which of the following devices can be used to connect the local LAN
to a wide area network (WAN) connection such as an ISDN line to a
remote city?
A. Bridge
B. Layer 2 switch
C. Repeater
D. Router
8.
Which of the following are most likely to be present in a modern
corporate internetwork that spans six cities in four states? (Select 3.)
A. Routers
B. Switches
C. Hubs
D. Routing Protocols
E. Repeaters
F. Bridges
9.
Foley wants to write a standard IP access list to block traffic from all
hosts coming from the IP address range 128.250.0.0 through to
128.250.255.255. Which of the following access lists will achieve
Foley's goal? (Select all that apply.)
A. access list 1 permit 128.250.0.0 0.0.0.0
B. access list 1 deny 128.250.0.0 0.0.0.0
C. access list 1 deny 128.250.255.255 255.255.0.0
D. access list 1 deny 128.250.254.254 0.0.255.255
E. access list 1 deny 128.250.0.0 0.0.255.255
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10.
Foley wants to set up an extended IP access list on a Cisco router to
block all Telnet access to the host 192.168.81.114. Which of the
following access lists will achieve this goal?
A. access list 105 deny tcp any host 192.168.81.114 eq telnet
B. access list 106 deny tcp 192.168.81.114 any host eq telnet
C. access list 107 deny tcp 192.168.81.114 0.255.255.255 any
host eq telnet
D. access list 108 deny tcp any host 192.168.81.114 eq http
11.
Which of the following WAN protocols do not provide error
correction?
A. SDLC
B. LAPB
C. HDLC
D. PPP
12.
Which of the following WAN protocols support STAC and Predictor
compression via Cisco's IOS?
A. PPP, LAPB, and HDLC
B. PPP and LAPB
C. PPP and HDLC
D. HDLC and LAPB
13.
Which of the following protocols are routing rather than routed
protocols? (Choose all that apply.)
A. RIPv2
B. IP
C. IPX
D. OSPF
E. EIGRP
14.
Which of the following protocols are routed rather than routing
protocols? (Choose all that apply.)
A. NWLink
B. DECnet
C. BGP
D. RIP
E. IGRP
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15.
Which of the following sets of IOS commands will set the IP address
of router RTR1's ethernet0 interface to 192.168.20.1 /28 and make it
active?
A. RTR1(config)#interface ethernet0
RTR1(config-if)#ip address 192.168.20.1 255.255.255.0
RTR1(config-if)#no shut
B. RTR1(config)#interface ethernet0
RTR1(config-if)#ip address 192.168.20.1 255.255.255.0
RTR1(config-if)#shut
C. RTR1(config)#interface ethernet0
RTR1(config-if)#ip address 192.168.20.1 255.255.255.240
RTR1(config-if)#no shut
D. RTR1(config)#interface ethernet0
RTR1(config-if)#ip address 192.168.20.1 255.255.255.240
RTR1(config-if)#shut
E. RTR1(config)#interface ethernet0
RTR1(config-if)#ip address 192.168.20.1 255.255.240.0
RTR1(config-if)#no shut
16.
Which of the following sets of IOS commands will set the IP address
of router ODLT1's ethernet1 interface to 10.10.40.1 /23 and make it
active?
A. ODLT1(config)#interface ethernet0
ODLT1(config-if)#ip address 10.10.40.1 255.255.240.0
ODLT1(config-if)#no shut
B. ODLT1(config)#interface ethernet0
ODLT1(config-if)#ip address 10.10.40.1 255.255.248.0
ODLT1(config-if)#no shut
C. ODLT1(config)#interface ethernet0
ODLT1(config-if)#ip address 10.10.40.1 255.255.252.0
ODLT1(config-if)#no shut
D. ODLT1(config)#interface ethernet0
ODLT1(config-if)#ip address 10.10.40.1 255.255.254.0
ODLT1(config-if)#no shut
E. ODLT1(config)#interface ethernet1
ODLT1(config-if)#ip address 10.10.40.1 255.255.254.0
ODLT1(config-if)#no shut
F. ODLT1(config)#interface ethernet1
ODLT1(config-if)#ip address 10.10.40.1 255.255.255.0
ODLT1(config-if)#no shut
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17.
You are interested in configuring a router so that it can be accessed
via a Telnet session from a remote host. Which of the following
passwords will you need to set for this option to be enabled?
A. Console password
B. Enable password
C. Auxiliary password
D. VTY password
18.
Which of the following passwords must be set before its
corresponding method of accessing the router becomes available?
A. Console password must be set before console access is available.
B. Enable password must be set before console access is available.
C. Auxiliary password must be set before access via the Auxiliary
port is available.
D. VTY password must be set before access via Telnet is available.
19.
Which of the following statements about VLANs are true? (Select
two.)
A. Each VLAN on a switch must be on a separate subnet.
B. Traffic passing between two ports on a switch that are members of
different VLANs must pass through Layer 3 of the OSI model.
C. Traffic passing between two ports on a switch that are members
of different VLANs only passes through Layer 2 of the OSI model.
D. Each VLAN on a switch must be on the same subnet.
20.
Which of the following are benefits of instituting VLANs on switches?
A. Broadcast traffic is only forwarded on those ports that are
members of the same VLAN.
B. Broadcast traffic is forwarded to all ports on the switch regardless
of VLAN membership.
C. Single VLANs can span multiple switches.
D. VLANs are limited to the ports on a single switch.
21.
Which of the following commands can be used to display which
particular ports are configured as members of each particular VLAN
configured on a Cisco Catalyst 1900 switch?
A. show vtp
B. show running-config
C. show spantree
D. show start-config
E. show vlan-membership
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22.
You are currently configuring a Catalyst 1900 switch's VLANs. You
want to configure ports 7–8 to VLAN 2, 9–10 to VLAN 3, and ports
11–12 to VLAN 4. Which of the following sets of command-line
instructions will do this?
A. switch(config-if)# interface e 0/7
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/8
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/9
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/10
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/11
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/12
switch(config-if)# vlan-membership static 2
B. switch(config-if)# interface e 0/7
switch(config-if)# vlan-membership static 1
switch(config-if)# interface e 0/8
switch(config-if)# vlan-membership static 1
switch(config-if)# interface e 0/9
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/10
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/11
switch(config-if)# vlan-membership static 3
switch(config-if)# interface e 0/12
switch(config-if)# vlan-membership static 3
C. switch(config-if)# interface e 0/7
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/8
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/9
switch(config-if)# vlan-membership static 3
switch(config-if)# interface e 0/10
switch(config-if)# vlan-membership static 3
switch(config-if)# interface e 0/11
switch(config-if)# vlan-membership static 4
switch(config-if)# interface e 0/12
switch(config-if)# vlan-membership static 4
D. switch(config-if)# interface e 0/7
switch(config-if)# vlan-membership static 4
switch(config-if)# interface e 0/8
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/9
switch(config-if)# vlan-membership static 3
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switch(config-if)# interface e 0/10
switch(config-if)# vlan-membership static 4
switch(config-if)# interface e 0/11
switch(config-if)# vlan-membership static 2
switch(config-if)# interface e 0/12
switch(config-if)# vlan-membership static 4
23.
Which of the following LAN hosts are most likely to require full rather
than half duplex ethernet connections? (Select two.)
A. File server
B. Workstation
C. Proxy server
D. Web server
24.
Which of the following devices can most effectively be used to
reduce network congestion caused by unicast transmissions by hosts
on the same segment?
A. Gateway
B. Repeater
C. Bridge
D. Router
E. Switch
25.
Which of the following devices can most effectively be used to
reduce congestion caused by broadcast transmissions by hosts on
the network? (Select all that apply.)
A. Repeater
B. Bridge
C Router
D. Switch (Layer 2)
E. Switch with VLAN
26.
Which of the following, when used while configuring an interface from
the command line on a Catalyst 1900 switch, will configure a port into
permanent trunk mode and start it negotiating with connected
devices to establish a link in trunk mode?
A. switch1(config-if)# trunking on
B. switch1(config-if)# trunk nonegotiate
C. switch1(config-if)# switch trunk enable
D. switch1(config-if)# switch enable trunk
E. switch1(config-if)# trunk on
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27.
Which of the following, when used while configuring a Catalyst 1900
switch from the command line, will set the VTP domain name to
ROOSLAN?
A. vtp enable set domain ROOSLAN
B. vtp server domain ROOSLAN
C. vtp domain set ROOSLAN
D. authenticate VTP domain ROOSLAN
E. connect VTP domain ROOSLAN
28.
Which of the following commands will correctly configure a Catalyst
1900 switch for in-band management on IP address 10.10.10.225
/29?
A. ip address 10.10.10.225 255.255.255.240
B. config ip 10.10.10.225 255.255.255.240
C. ip address 10.10.10.225 255.255.255.224
D. config ip 10.10.10.225 255.255.255.224
E. ip address 10.10.10.225 255.255.255.248
F. config ip 10.10.10.225 255.255.255.248
29.
Which of the following commands will allow a Catalyst 1900 switch to
be correctly configured with an addressable (one that is neither
broadcast or network address) IPv4 address?
A. ip address 10.10.99.224 255.255.255.240
B. ip address 10.10.34.239 255.255.255.248
C. ip address 10.10.154.91 255.255.255.224
D. ip address 10.10.72.127 255.255.255.224
E. ip address 10.10.105.31 255.255.255.252
30.
You have the following access list:
access-list 1 deny 192.168.10.1 0.255.255.255
access-list 1 deny 10.10.20.1 0.0.255.255
access-list 1 permit 10.15.30.1 0.0.0.255
applied to incoming traffic on the ethernet0 interface. No other
access lists have been applied on the router. Given this information,
which of the following statements is true? (Choose all that apply.)
A. Traffic from host address 192.168.10.20 entering the router from
interface ethernet0 will be blocked.
B. Traffic from host address 192.168.20.1 entering the router from
interface ethernet0 will be blocked.
C. Traffic from host address 10.10.100.155 entering the router from
interface ethernet0 will be allowed.
D. Traffic from host address 10.90.100.10 entering the router from
interface ethernet0 will be allowed.
E. Traffic from host address 10.240.34.8 entering the router from
interface ethernet0 will be blocked.
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31.
You have the following extended access list applied to inbound traffic
on interface Ethernet 0 on a Cisco router.
access-list 101 allow tcp any host 192.168.10.21 eq 80
access-list 101 deny tcp 10.10.20.0 0.0.0.255 192.168.10.21 eq ftp
access-list 101 allow tcp 10.10.20.0 0.0.255.255 192.168.10.22 eq
telnet
No other access lists have been applied on Ethernet 0 or any other
interfaces on this router. Given this particular access list, which of the
following statements are false? (Choose all that apply.)
A. All traffic incoming on interface Ethernet 0 for the Web server
hosted on host 192.168.10.21 will be allowed.
B. All traffic incoming on interface Ethernet 0 for the SSL secured
Web site hosted on host 192.168.10.21 will be allowed.
C. FTP traffic coming from host 10.100.20.10 to host 192.168.10.21
via interface Ethernet 0 will be blocked.
D. FTP traffic coming from host 10.10.20.10 to host 192.168.10.21
via interface Ethernet 0 will be allowed.
E. Telnet traffic coming from host 10.10.50.30 to host 192.168.10.21
via interface Ethernet 0 will be allowed.
F. Telnet traffic coming from host 10.20.50.30 to host 192.168.10.22
via interface Ethernet 0 will be blocked.
32.
Which of the following are properties of frame relay networks?
A. Frame relay networks are multi-access networks.
B. In frame relay, routers are called data communications equipment.
C. In frame relay, switches are called data terminal equipment.
D. The line between a router and the nearest frame relay switch is
termed the access link.
E. Virtual circuits can only exist between switches of the same make
and manufacture.
33.
Which of the following frame relay acronyms matches its definition?
A. DTE: Switches in a frame relay service.
B. DCE: Routers in a frame relay service.
C. SVC: A pre-configured virtual circuit between two DTE.
D. CIR: Length of time of which agreed bandwidth can be exceeded.
E. DLCI: Frame relay address used to identify a virtual circuit.
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34.
Rooslan has the following list of addresses used on a network:
Address 1: 00-10-5A-6D-50-40
Address 2: 00-10-5A-6D-38-24
Address 3: 10.28.12.73
Address 4: 10.12.05.77
Address 5: SERVER1
Address 6: primus.lspace.org
Which of these addresses are examples of Layer 2 addresses as
defined in the OSI model? (Select all that apply.)
A. Address 1
B. Address 2
C. Address 3
D. Address 4
E. Address 5
F. Address 6
35.
Which of the following correctly describes a MAC address?
A. A 12-character fixed address made up of numerals 0–9
characters A–F.
B. A 12-character dynamic address made up of numerals 0–9
characters A–F.
C. A 32-bit fixed binary address.
D. A 32-bit dynamic binary address.
E. A 24-character fixed address made up of numerals 0–9
characters A–F.
F. A 24-character dynamic address made up of numerals 0–9
characters A–F.
36.
and
and
and
and
Which of the following networking devices is paired with the layer of
the OSI model that would best describe its core functionality? (Select
all that apply.)
A. Repeater, Layer 1.
B. Bridge, Layer 2.
C. Switch, Layer 4.
D. Router, Layer 3.
E. Gateway, Layer 3.
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37.
You are investigating the OSI model as a way of understanding how
different networking devices operate on the LAN. Which of the
following descriptions has a correct match between the description of
data transferred, the device used, and the layer of the OSI model
that this process occurs at? (Select all that apply.)
A. Repeaters work with bits at Layer 2.
B. Bridges work with packets at Layer 1.
C. Switches work with frames at Layer 2.
D. Routers work with packets at Layer 3.
E. Routers work with frames at Layer 2.
F. Bridges work with packets at Layer 3.
G. Switches work with packets at Layer 1.
38.
You are the administrator of a LAN that includes four different
buildings that are in geographic proximity. Each building has its own
router. The router in Building 1 is connected to ISDN lines that go to
Building 2 and Building 3. The router in Building 2 is connected to
ISDN lines that connect it to Building 1 and Building 4. The router in
Building 1 fails. Which of the following statements are true? (Select
all that apply.)
A. Hosts in Building 4 will be able to contact hosts in Building 2.
B. Hosts in Building 2 will be able to contact hosts in Building 3.
C. Hosts in Building 1 will be unable to contact hosts in any other
buildings.
D. Hosts in Building 4 will be able to contact hosts in Building 3.
39.
You are the administrator of a LAN where VLANs have been
instituted. Switch 1 has been configured to host VLANs 1 and 2.
Switch 2 is connected to switch 1 and hosts VLAN 2. Switch 3 is
connected to Switch 1 and hosts VLANs 1 and 3. Switch 4 is
connected to Switch 3 and hosts VLANs 3 and 4. Switch 3 fails.
Which of the following statements are true? (Select all that apply.)
A. Some hosts on VLAN 1 will be able to contact hosts on VLAN 2
B. All hosts on VLAN 1 will be able to contact hosts on VLAN 2
C. Hosts on VLAN 4 will be able to contact some hosts on VLAN 3
D. Hosts on VLAN 2 will be able to contact hosts on VLAN 4
40.
You are interested in logging messages each time a router intercepts
or transmits an RIP update on a TCP/IP network. Which of the
following IOS commands will do this?
A. debug ip rip
B. debug ip igrp
C. log rip updates
D. log igrp updates
E. audit ip rip
F. audit ip igrp
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41.
You want to configure a router to log messages detailing IGRP
updates received and sent by the router. Which of the following IOS
commands would you use to do this?
A. audit
B. debug
C. log
D. watch
E. show
42.
Which of the following IPv4 addresses exist within the private
address space? (Select all that apply.)
A. 10.99.244.203
B. 172.168.33.28
C. 172.16.24.193
D. 192.169.0.103
E. 192.168.23.12
43.
Rooslan is looking at utilizing a private IP address range for a 240host network. He wants to allocate a single /24 subnet to this task.
Which of the following subnets are located within the private IP
address space as defined by RFC 1918 and meet Rooslan's
requirements? (Select all that apply.)
A. 11.128.120.0 /27
B. 172.17.119.0 /24
C. 172.32.161.0 /24
D. 192.168.0.192 /27
E. 192.168.101.0 /24
44.
Which of the following IP address/subnet mask combinations cannot
be used, as they represent either the network address or broadcast
address of that specific network? (Choose all that apply.)
A. IP: 10.10.10.255, Subnet Mask: 255.255.255.0
B. IP: 10.10.10.224, Subnet Mask: 255.255.255.240
C. IP: 10.10.192.224, Subnet Mask: 255.255.224.0
D. IP: 10.10.10.192, Subnet Mask: 255.255.255.252
E. 1IP: 10.10.252.254, Subnet Mask: 255.255.252.0
45.
You are attempting to debug some IP address/subnet mask
combinations that appear not to be working. Which of the following IP
addresses are not addressable hosts given the corresponding subnet
masks? (Choose all that apply.)
A. IP: 192.168.1.0 /24
B. IP: 192.168.224.0 /20
C. IP: 192.168.224.0 /18
D. IP: 192.168.240.0 /19
E. IP: 192.168.240.0 /21
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46.
You have a host named ALPHA on a TCP/IP subnet that can
communicate with other hosts on the same subnet, but cannot
communicate with hosts on other subnets. Other hosts on the
original TCP/IP subnet can communicate with host ALPHA as well as
hosts on remote subnets. Hosts on remote subnets cannot
communicate with host ALPHA. Which of the following are possible
reasons for this problem? (Select two.)
A. The subnet mask on ALPHA is incorrectly set.
B. The default gateway on ALPHA is incorrectly set.
C. The IP address of ALPHA conflicts with another host on the same
subnet.
D. The DNS server address on ALPHA is incorrectly set.
47.
You have a LAN with a single TCP/IP subnet. Your network is
connected to the Internet via an ISDN line to your ISP. This ISDN
line runs via a Cisco router. In the last hour you have noticed that
you are unable to browse any Web sites, nor have you received any
email from outside your network. You are able to ping your router,
but not the ISP's router. Which of the following network devices could
be at fault? (Select two.)
A. The UTP cabling between your computer and the switch.
B. The switch at your office may have failed.
C. The router at your office may have failed.
D. The ISDN line between your office and the ISP may have failed.
E. The router at the ISP connected to your ISDN line may have
failed.
48.
You are attempting to troubleshoot the following access list which
has been applied to inbound traffic on interface Ethernet 0 on a
Cisco router.
access-list 10 permit 10.20.30.0 0.0.255.255
access-list 10 permit 10.30.20.0 0.0.255.255
access-list 10 permit 10.50.30.0 0.255.255.255
access-list 10 deny 10.60.20.0 0.0.255.255
access-list 10 deny 10.40.20.0 0.0.255.255
You are attempting to ascertain why traffic from the host 10.60.20.55
is able to pass through interface Ethernet 0. No other access lists are
currently in use on the router. Which of the following reasons
explains this?
A. There is an implicit allow at the end of all access lists.
B. Line four of the access list should be re-written as "access-list 10
deny 10.60.20.0 255.255.0.0."
C. Line three of the access list permits all traffic from the 10.x.x.x
range of host addresses.
D. Line one of the access list permits all traffic from the 10.x.x.x
range of host addresses.
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49.
You are attempting to troubleshoot the following extended access list
which has been applied to interface Ethernet 0 on a Cisco router:
access-list 101 permit tcp 10.10.0.0 0.0.255.255 192.168.10.22 eq
80
access-list 101 permit tcp 10.20.0.0 0.0.255.255 192.168.10.22 eq
23
access-list 101 deny tcp 10.30.0.0 0.0.255.255 192.168.10.22 eq
80
access-list 101 deny tcp 10.40.0.0 0.0.255.255 192.168.10.22 eq
23
access-list 101 permit tcp 10.50.0.0 0.0.255.255 192.168.10.22 eq
80
A particular host with IP address 10.40.22.23 is unable to access the
Web server hosted on host 192.168.10.22. Which of the following is
the reason for this?
A. The fourth line of the access list only grants host on the 10.40.x.x
network access to port 23 of host 192.168.10.22.
B. The third line of the access list denies hosts on the 10.40.x.x
network access to port 80 of host 192.168.10.22.
C. The first line of the access list denies hosts on the 10.40.x.x
network access to port 80 of host 192.168.10.22.
D. The implicit deny statement at the end of all access lists means
that packets from network 10.40.x.x destined for port 80 on host
192.168.10.22, which aren't covered by any of the lines in the access
list, are discarded.
50.
You are currently using STAC compression on a WAN link but are
concerned that CPU utilization might be too high on the routers on
either end. Which of the following IOS commands will display the
CPU utilization on a router for five seconds, at one-minute and fiveminute intervals?
A. show utilization
B. show process
C. show compress
D. show CPU
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51.
Which of the following statements about PPP authentication
protocols are true? (Select two.)
A. When PAP is used over a WAN connection, username and
password are sent by the dialing router without encryption.
B. When CHAP is used over a WAN connection, username and
password are sent by the dialing router without encryption.
C. When PAP is used over a WAN connection, the router receiving
the connection sends a challenge which includes a random number
later input into the MD5 hash algorithm.
D. When CHAP is used over a WAN connection, the router receiving
the connection sends a challenge which includes a random number
later input into the MD5 hash algorithm.
52.
Which of the following are benefits of implementing Spanning Tree
Protocol (STP) on Cisco switches on a local area network? (Select
two.)
A. STP stops frames from looping indefinitely in switch-based LANs
that have been configured with redundant links.
B. STP allows more than one active path to exist at any time
between collision domains.
C. STP allows only one active path to exist at any time between
collision domains.
D. STP allows frames to loop indefinitely in switch-based LANs that
have been configured with redundant links.
53.
There are five switches in a network, ALPHA, BETA, GAMMA,
DELTA, and EPSILON. Each switch is connected to each other
switch. Spanning Tree Protocol is in use on this network. STP elects
switch BETA as the root bridge. Which of the listed switches will
have ports that will not transmit frames received from other ports or
forward received frames? (Select all that apply.)
A. ALPHA
B. BETA
C. GAMMA
D. DELTA
E. EPSILON
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54.
One of the LANs that you administrate has STP operational on all of
its 16 Cisco Catalyst 1900 switches. You are connected to the switch
via the console and would like to display the spanning tree
information for VLAN 2. Which of the following commands will enable
you to do this?
A. show spantree 2
B. show spantree 1
C. show trunk
D. show cdp neighbors
E. show config vlan 2
55.
You wish to view the statistics about STP BPDU communications.
Which of the following commands can be used while connected to a
Catalyst 1900 switch's console port to display this information?
A. display spantree statistics
B. show spantree statistics
C. display bpdu statistics
D. show bpdu statistics
E. show spantree
56.
LAN A consists of 20 hosts with 100Mbps network cards all
connected via Cat 5 UTP to a single 25-port 100Mbps Hub. LAN B
consists of 20 hosts with 100Mbps network cards all connected via
Cat 5 UTB to a single 25 port 10Mbps switch. Which of the following
reasons best explains why LAN B often has better performance than
LAN A when all hosts are in use?
A. Under no circumstances will LAN B have better performance than
LAN A.
B. Broadcast traffic from every host on LAN A will be transmitted to
every other host on LAN A. Broadcast traffic from every host on LAN
B will only be transmitted to a single destination host.
C. Unicast traffic from each host on LAN A will be transmitted to
every other host on LAN A. Unicast traffic from each host on LAN B
will only be transmitted to a single destination host.
D. Unicast traffic from each host on LAN A will be transmitted to a
single destination host. Unicast traffic from each host on LAN B will
be transmitted to all other hosts on LAN B.
57.
Which of the following routing protocols are classified as "Exterior
Routing Protocols"?
A. RIPv2
B. BGP
C. IGRP
D. EIGRP
E. OSPF
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58.
Which of the following routing protocols are classified as "Interior
Routing Protocols"? (Choose all that apply.)
A. RIPv2
B. BGP
C. IGRP
D. EIGRP
E. OSPF
59.
Which of the following is the maximum routing metric value (noninfinite) of the RIP routing protocol?
A. 10 hops
B. 15 hops
C. 16 hops
D. 255 hops
E. 256 hops
F. 1024 hops
60.
Which of the following can IGRP use in the calculation of its routing
metrics? (Choose all that apply.)
A. Bandwidth
B. Delay
C. Load
D. Reliability
E. MTU
F. IOS Version
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Answer Key 640-811
1. B
2. D
3. D
4. B, D
5. A, B
6. A, B
7. D
8. A, B, D
9. D, E
10. A
11. C
12. B
13. A, D, E
14. B, D
15. C
16. E
17. D
18. C, D
19. A, B
20. A, C
21. E
22. C
23. A, C
24. E
25. C, E
26. E
27. B
28. E
29. C
30. A, B, E
31. B, D, E
32. A, D
33. E
34. A, B
35. A
36. A, B, D
37. C, D
38. A, C
39. A, C
40. A
41. B
42. A, C, E
43. B, E
44. A, B, D
Cisco CCNA (640-801).doc
300
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
A, B, E
A, B
D, E
C
D
B
A, D
A, C
A, C, D, E
A
B
C
B
A, C, D, E
B
A, B, C, D, E
1.
Answer B is the correct solution. It assigns the correct number of
switches to each floor. Answer C is incorrect because it does not assign
the correct number of switches to each floor. Answers A and D are
incorrect because they use repeaters to connect the two floors. The
distance between the two floors is at most 12 meters, far less than what
is required for repeaters. Repeaters will also do nothing to help route
traffic. Separate subnets were introduced to remove a congestion
problem.
2.
Answer D is the correct answer. As congestion from unicast traffic
appears to be the problem, the best solution is to replace the 20-port,
10Mbps hub with a Cisco Catalyst 2950 10/100Mbps hub. This will not
only improve the bandwidth from 10 to 100Mbps (assuming that the
hosts have compliant Ethernet cards) but will also reduce the problem
of unicast congestion. Answer B is incorrect because there is no
wireless network. Answer A is incorrect because this situation does not
call for a router. Answer C is incorrect because although a 100Mbps
hub will increase performance, it will not remove the unicast traffic
problem, as hubs forward unicast traffic on all ports. The performance
difference between a hub and a switch is quite significant.
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3.
Answer D is correct. Class C address spaces have the subnet mask
255.255.255.0. This allows for a maximum of 254 addressable hosts on
the network. When a class C address space is subnetted, a certain
amount of hosts are allowed for each particular subnet mask. A subnet
mask of 255.255.255.128 allows 126 addressable hosts. A subnet mask
of 255.255.255.192 allows 62 addressable hosts. A subnet mask of
255.255.255.224 allows 30 addressable hosts. A subnet mask of
255.255.255.240 allows 14 addressable hosts. Answers A, B, and C are
incorrect because the subnet masks for each location and the host
addresses are incorrect.
4.
Answers B and D are correct. Answer B provides for 510 hosts in
Minneapolis, which meets the 300 host requirement. It provides for 254
hosts in Melbourne, which meets the 120 host requirement. It provides
for 254 hosts in Vancouver, which meets the 28 host requirement.
Answer D is correct as it provides 510 hosts in Minneapolis, 216 in
Melbourne, and 62 in Vancouver. To support 300 hosts, a subnet mask
of 255.255.254.0 or lower is required. In CIDR notation this is /23 or
lower. To support 120 hosts, a subnet mask of 255.255.255.128 or
lower is required. In CIDR notation this is /25 or lower. To support 28
hosts, a subnet mask of 255.255.255.224 or lower is required. In CIDR
notation this is /27 or lower. Answer A is incorrect because it does not
provide enough host addresses for the Minneapolis site. Answer C is
incorrect because it does not provide enough host addresses at the
Minneapolis site.
5.
Answers A and B are correct. RIP and RIPv2 have a maximum hop
count of 15 hops and hence would not be able to map the entire
network at this university. Answer C is incorrect, as IGRP can handle
routes in excess of 25 hops. Answer D is incorrect, as EIGRP can
handle routes with hop counts in excess of 25 hops. Answer E is
incorrect, as OSPF can all handle routes with hop counts in excess of
25 hops.
6.
Answers A and B are correct. Answer A is correct, as RIPv2 is an open
protocol standard supported by a multitude of vendors. Answer B is
correct, as OSPF is an open protocol standard supported by a multitude
of vendors. Answer C is incorrect, as Interior Gateway Routing Protocol
(IGRP) was developed and is owned by Cisco. Answer D is incorrect,
as Enhanced Interior Gateway Routing Protocol (EIGRP) is a
proprietary routing protocol developed by Cisco. Proprietary means that
unless a vendor has specifically licensed the protocol implementation
from Cisco, a third-party vendor will not support it.
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7.
Answer D is correct. Routers generally form the border between a LAN
and a WAN link such as an ISDN line or a Frame Relay connection.
Answer A is incorrect, as bridges do not perform this function. Answer B
is incorrect, as Layer 2 switches cannot perform this function. Answer C
is incorrect, as repeaters cannot perform this function.
8.
Answers A, B, and D are correct. In this question you are asked to
apply your judgment even though more than three answers could be
correct. Cisco occasionally does this on its associate level exams. Of
the six possibilities listed, routers, switches, and routing protocols are
the most likely to be present in a modern corporate internetwork.
Answer C is incorrect. Although hubs are possible, in general most
networks have upgraded their hubs to switches. Apart from their
wireless hubs, Cisco does not sell dedicated hubs anymore. Answer E
is incorrect. Although repeaters do appear on corporate networks, they
are not as likely to appear as routers, switches, and routing protocols.
Answer F is incorrect. Bridges do appear on some modern networks,
but like hubs they have been phased out in favor of newer technologies.
9.
Answers D and E are correct. Answer D is correct because the first two
quads are 128.250 and the mask specifies that they must be fixed. The
last two quads are wild according to the mask. This will block the
requisite traffic. Answer E is correct because the first two quads are
128.250 and the mask specifies that they must be fixed. The last two
quads are wild according to the mask. This will block the requisite
traffic. Access list B is incorrect as this will only block traffic from
address 128.250.0.0. Access list C is incorrect as this will block traffic
from all hosts except those whose last two quads equal 255. The secret
to understanding access lists is to understand how the wildcard masks
work. A 0 in the wildcard mask means that the corresponding quad
must match. For example, in access list 1, A.B.C.D 0.0.255.255, any IP
address that starts A.B will be covered by the access list. There can be
any values for C and D but it will still be covered by this list.
10.
Answer A is correct. The syntax of an extended IP access list is accesslist [list number] {deny|permit} protocol source source-wildcard
destination destination-wildcard eq port/protocol name (for example,
http, telnet, ftp). Answer A is correct because the source is any host and
the destination is the host specified in the question, 192.168.81.114.
The protocol specified is telnet. Answer B is incorrect, as this will block
telnet traffic from host 192.168.81.114 to any host, but not prevent
telnet traffic to this host. Answer C is incorrect as it will block all telnet
traffic from network 192.0.0.0 /8. Answer D is incorrect as it deals with
http rather than telnet traffic.
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11.
Answer C is correct. The question asks which protocols do not provide
error correction. Although all WAN protocols provide error detection, the
HDLC (High Level Data-Link Control) protocol does not provide error
correction capability. Essentially HDLC will acknowledge that there is an
error, but do nothing further. Answer A is incorrect, as SDLC can
correct errors. Answer B is incorrect, as LAPB can correct errors.
Answer D is incorrect, as PPP can correct errors.
12.
Answer B is correct. PPP and LAPB (Link Access Procedure Balanced)
WAN protocols support STAC (named for STAC electronics) and
Predictor compression via Cisco's IOS. PPP also supports the MPPC
(Microsoft Point to Point Compression) method of compression. Answer
A is incorrect, as HDLC only supports the STAC method of
compression via Cisco's IOS, it does not support Predictor. Answer C is
incorrect, as HDLC only supports the STAC method of compression via
Cisco's IOS; it does not support Predictor. Answer D is incorrect, as
HDLC only supports the STAC method of compression via Cisco's IOS;
it does not support Predictor.
13.
Answers A, D, and E are correct. Answer A is correct, as RIPv2 is a
routing protocol. Answer D is correct, as OSPF is a routing protocol.
Answer E is correct, as EIGRP is a routing protocol. Answer B is
incorrect, as IP is a routed protocol. Answer C is incorrect, as IPX is a
routed protocol. Routing protocols inform routers of routes through the
network. Routed protocols carry data traffic.
14.
Answers A and B are correct. Answer A is correct, as NWLink is a
routed protocol. Answer B is correct, as DECnet is a routed protocol.
Answer C is incorrect, as BGP is a routing protocol. Answer D is
incorrect, as RIP is a routing protocol. Answer E is incorrect, as IGRP is
a routing protocol.
15.
Answer C is correct. 192.168.20.1 /28 would translate as 192.168.20.1
255.255.255.240 in dotted decimal notation. This eliminates all but
answers C and D. NO SHUT makes an interface active, making C the
correct answer. Answer A is incorrect because it sets the incorrect
subnet mask. Answer B is incorrect because it sets the incorrect subnet
mask. Answer D is incorrect because it shuts down the interface.
Answer E is incorrect, as it sets the incorrect subnet mask.
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16.
Answer E is the correct answer. There are two things to look for in
answering this question. The first is that the correct Ethernet interface
on the router is being addressed—in this case ethernet1 instead of
ethernet0. Answer A is incorrect, as Ethernet0 is being configured.
Answer B is incorrect, as Ethernet0 is being configured. Answer C is
incorrect, as Ethernet0 is being configured. Answer D is incorrect, as
Ethernet0 is being configured. The second is to realize that /23
translates into decimal quad notation as 255.255.254.0. Answer F is
incorrect, as it has the wrong subnet mask.
17.
Answer D is correct The VTY password needs to be set before a router
can be accessed remotely via the telnet protocol. Answer A is incorrect;
the console password is used for those connections via console cable
rather than remote telnet connections. Answer B is incorrect, as the
enable password is used to enter privileged mode. Answer C is
incorrect, as the auxiliary password is used for access via the auxiliary
port.
18.
Answers C and D are correct. Answer C is correct. The Auxiliary
password must be set before access is available via the auxiliary port.
Answer D is correct. The VTY password must be set before access is
available via Telnet is available. Answer A is incorrect. Access is
available from the console port regardless of whether a console
password is set. Answer B is incorrect. Access is available from the
console port regardless of whether the enable password has been set.
19.
Answers A and B are correct. Answer A is correct. Each VLAN on a
switch must reside on a separate logical subnet. Answer B is correct.
Traffic passing between two ports on a switch that are members of
separate VLANs must be transferred via a process at Layer 3 of the
OSI model. Answer C is incorrect. Intra-VLAN traffic must pass through
Layer 3. Answer D is incorrect; VLANs on the same switch must be on
separate subnets.
20.
Answers A and C are correct. Answer A is correct. One of the benefits
of instituting VLANs is that it provides a way of limiting broadcast traffic
to those ports that are members of the same VLAN. Answer C is
correct. VLANs can also be configured on multiple switches. A
broadcast frame transmitted on a port that is a member of VLAN 1 on a
particular switch will not only be transmitted to all other ports that are
members of VLAN 1 on that switch, but to ports on other switches
connected to that switch that are also members of VLAN 1. Answer B is
incorrect; broadcast traffic is only forwarded to ports on a switch that
are members of the same VLAN. Answer D is incorrect; VLANs can
span multiple compatible switches.
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21.
Answer E is the correct answer. The IOS command to display the
membership of VLANS on a switch is show vlan-membership. Answer A
is incorrect because show vtp will display VTP status. Answer B is
incorrect. show running-config is used on routers to display their
configuration. Answer C is incorrect. Show spantree [vlan] will display
the spanning tree information for a particular VLAN. Answer D is
incorrect. show start-config is used on routers to display their startup
configuration.
22.
Answer C is correct. Only answer C assigns each port to its correct
VLAN. The other answers assign ports to incorrect VLANs. This
question looks exceedingly complex, but can be reduced to the correct
answer by eliminating obviously incorrect possibilities. Answer A is
incorrect, as port 9 through 12 are assigned to the wrong VLAN.
Answer B is incorrect, as port 7 is assigned to VLAN 1 instead of VLAN
2. Answer D is incorrect, as it assigns port 7 to VLAN 4 rather than
VLAN 2.
23.
Answers A and C are correct. Answer A is correct, as a file server is
likely to send and receive a lot of information on the network. Answer C
is correct, as a proxy server is likely to send and receive a lot of
information on the network. Answer B is incorrect. Although there will be
cases where workstations will want to send and receive at the same
time, it is less critical than for the file and proxy server. Answer D is
incorrect. Web servers tend to receive small amounts of incoming data
yet provide large amounts of outgoing data. Even though you would
most likely configure a Web server to also be full duplex, its
requirements are not as great as that of the proxy or file server. This
question again asked you to exercise a best choice given available
options.
24.
Answer E is correct. A switch will most effectively reduce unicast
transmissions by hosts on the same segment by reducing the segment
size to only the hosts connected to a single port (usually one). Answer
B is incorrect. Repeaters forward all traffic and will do nothing to alter
the size of a segment. Answer C is incorrect. Although a bridge will
reduce network congestion caused by unicast transmission, it will not
do so as effectively as a switch. Answer D is incorrect. Routers can
reduce the size of segments, but will not do so as effectively as
switches.
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25.
Answers C and E are correct. Answer C is correct. A router can reduce
congestion caused by broadcast traffic. Answer E is correct. A switch
that is configured with VLANs can reduce congestion caused by
broadcast traffic. Answer A is incorrect. Repeaters forward broadcast
traffic. Answer B is incorrect. Bridges forward broadcast traffic. Answer
D is incorrect. Layer 2 switches forward broadcast traffic.
26.
Answer E is correct. trunk on will configure a port into trunk mode and
start it negotiating with connected devices to establish a link in trunk
mode. Answer A is incorrect, as it presents incorrect syntax. Answer B
is incorrect, as trunk nonegotiate bypasses this negotiation phase.
Answer C is incorrect, as it represents incorrect syntax. Answer D is
incorrect, as it represents incorrect syntax. Note that the configuration
commands on a Catalyst 1900 switch can be different to those on other
switches.
27.
Answer B is correct. vtp server domain ROOSLAN will set the vtp
domain name to ROOSLAN on a Catalyst 1900 switch. Answer A has
incorrect syntax. Answer C has incorrect syntax. Answer D has
incorrect syntax. Answer E has incorrect syntax. Other models of Cisco
switch, such as the 6000 series, use the set vtp domain domainname
command to set the vtp domain.
28.
Answer E is correct. You need to change the CIDR notation of /29 to
dotted decimal subnet notation. /29 is equivalent to 255.255.255.248. IP
addresses are set on switches using the ip address ip-address subnetmask command. Answer A is incorrect, as it presents the wrong subnet
mask. Answer B is incorrect, as it presents the wrong subnet mask.
Answer C is incorrect, as it presents the wrong subnet mask. Answer D
is incorrect, as it presents the wrong subnet mask. Answer F is
incorrect, as the config ip command will not perform the specified
function.
29.
Answer C is correct. Answer C represents the only answer where a
network or broadcast address for a given network is not listed. Answer
A is incorrect, as this is a network address given this subnet mask.
Answer B is incorrect, as this is a broadcast address given this subnet
mask. Answer D is incorrect, as this is a broadcast address given this
subnet mask. Answer E is incorrect, as this is a broadcast address
given this subnet mask. This question is answered by calculating which
of the IP addresses listed are actually fully addressable given the
corresponding subnet masks.
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30.
Answers A, B, and E are correct. Answer A is correct. Traffic from
192.168.10.20 will be blocked at the first line of the access list. Answer
B is correct. Traffic from host 192.168.20.1 will be blocked by the first
line of the access list. Answer E is correct. Traffic from host 10.240.34.8
will be blocked, as it is not allowed by the third line of the access list
and hence will be implicitly denied. Answer C is incorrect. Traffic from
host 10.10.100.155 will be blocked by line 2 of the access list. Answer
D is incorrect. Traffic from host address 10.90.100.10 will be blocked by
the implicit deny at the end of the access list. The first line of this
access list denies traffic coming from any host from 192.X.X.X. That
means if the first quad of the host address is 192, the traffic will be
discarded. The second line of the access list denies traffic coming from
any host with the address 10.10.X.X. The third line of the access list
allows traffic from any host with the address 10.15.30.x. At the end of
any access list is an implicit deny statement.
31.
Answers B, D, and E are correct. Recall that the question asked for
which statements are false rather than true. So although these answers
are false, they are correct in this context. Answer B is false (hence
correct) as traffic accessing the SSL Web site on host 192.168.10.21
will be blocked by the implicit deny at the end of the access list. Answer
D is false (hence correct), as line 2 of the access list will block this
traffic. Answer A is true (hence incorrect). The first line of the access list
makes statement A true. Answer C is true (hence incorrect). Line two of
the access list blocks FTP traffic from 10.x.x.x to the FTP server on
192.168.10.21. Answer F is true (hence incorrect). Because of the
implicit deny at the end of all access lists, telnet traffic coming from host
10.20.50.30 (not covered by any access list entry) will be blocked.
32.
Answers A and D are correct. Answer A is correct. Frame relay
networks are multi-access, which means that they can have more than
two end points. Answer D is correct. The line between a router and the
nearest frame relay switch is the access link. Answer B is incorrect.
Routers are referred to as data terminal equipment. Answer C is
incorrect. Switches are referred to as data communications equipment.
Answer E is incorrect. Virtual circuits exist between DTE/routers.
33.
Answer E is correct. DLCI is the frame relay address used to identify a
virtual circuit. Answer A is incorrect. DTE (Data Terminal Equipment) is
the routers that form endpoints in a frame relay system. Answer B is
incorrect. DCE (Data Communications Equipment) is the switches that
carry frame relay traffic. Answer C is incorrect SVC (Switched Virtual
Circuit) is a dynamic rather than static virtual circuit that exists as
required. Answer D is incorrect. CIR (Committed Information Rate) is
the agreed upon bandwidth of the VC.
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34.
Answers A and B are correct. Answer A is correct as it represents a
MAC or Ethernet address. Answer B is correct as it represents a Mac or
Ethernet address. Layer 2 addresses are made up of a 12-digit
hexadecimal sequence. These addresses are written to the network
card. Answer C is incorrect. IP addresses are represented at Layer 4 of
the OSI model. Answer D is incorrect. IP addresses are represented at
Layer 4 of the OSI model. Answer E is incorrect, as it is a NetBIOS
rather than MAC/Ethernet address. Answer F is incorrect, as it is an
FQDN address (used by DNS) rather than a MAC address.
35.
Answer A is correct. A MAC address is made up of 12 characters
consisting of the numerals 0–9 and characters A–F. This can be
expressed more simply by saying 12 hexadecimal characters.
Hexadecimal is Base16 to decimal's Base10; the extra numbers in
hexadecimal are represented by the characters A–F. Answer B is
incorrect. MAC addresses are fixed rather than dynamically allocated.
Answer C is incorrect. MAC addresses are not binary but hexadecimal.
Answer D is incorrect. MAC addresses are not binary but hexadecimal.
Answer E is incorrect; MAC addresses are 12 characters in length.
Answer F is incorrect, MAC addresses are 12 characters in length and
static.
36.
Answers A, B, and D are correct. Answer A is correct. Repeaters
operate at Layer 1 of the OSI model. Answer B is correct, as bridges
operate at Layer 2. Answer D is correct; routers operate at Layer 3 of
the OSI model. Answer C is incorrect; switches operate at Layer 2.
Answer E is incorrect; gateways (which provide protocol translation)
operate at Layers 4, 5, 6, and 7. Some devices such as switches have
multiple layer functionality, hence the term Layer 3 switching. However,
the question asked about the core functionality, and the core
functionality of a switch is to shift frames at Layer 2.
37.
Answers C and D are correct. Answer C is correct. Switches work with
frames at Layer 2. Answer D is correct. Routers work with packets at
Layer 3. Answer A is incorrect. Repeaters work with bits at Layer 1.
Answer B is incorrect; bridges work with frames at Layer 2. Answer E is
incorrect; routers work with packets at Layer 3. Answer F is incorrect.
Bridges work with frames, and routers work with packets at Layer 3.
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38.
Answers A and C are correct. Answer A is correct. Even though the
router in building one has failed, this does not influence the connectivity
of building two to building four which are directly linked. Answer C is
correct. If it has no router, hosts in building one cannot contact hosts in
other buildings. Answer B is incorrect. The path between buildings two
and three goes through building one. If the router in building one fails,
these hosts will be unable to communicate. Answer D is incorrect. The
path between building four and building three exists through buildings
two and one. If building one's router is down, this path is broken.
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39.
Answers A and C are correct. Answer A is correct. Although there are
some hosts on VLAN 1 that are hosted off switch 3, there are some that
are hosted off switch 1 and switch 2—hence these will still be able to
contact each other. Answer C is correct. As switch 4 has hosts on both
VLAN 3 and VLAN 4, some of these hosts will be able to contact each
other regardless of the status of switch 3. Answer B is incorrect, as
some hosts on VLAN 1 were hosted off switch 3. Because the
connection between VLAN 2 and VLAN 4 goes through switch 3,
answer D is incorrect.
40.
Answer A is correct. The correct syntax of the IOS command to log a
message each time a router intercepts or transmits an RIP update on a
TCP/IP network is debug ip rip. Answer B is incorrect. IGRP is another
routing protocol, Interior Gateway Routing Protocol. Answer C is
incorrect; this syntax is invalid. Answer D is incorrect; this syntax is
invalid. Answer E is incorrect; this syntax is invalid. Answer F is
incorrect; this syntax is invalid.
41.
Answer B is correct. The debug command can be used to write
messages to a log file for later examination in understanding a router's
performance. Answer A is incorrect, as this command does not exist.
Answer C is incorrect, as this command does not exist. Answer D is
incorrect, as this command does not exist. Answer E is incorrect; the
show command does not perform this function.
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42.
Answers A, C, and E are correct. The private IP address range as
defined by RFC 1918 is 10.0.0.0–10.255.255.255 for Class A,
172.16.0.0– 172.31.255.255 for Class B, and 192.168.0.0–
192.168.255.255 for Class C. Answer A is correct, as this address falls
within the Class A private range. Answer C is correct, as this falls within
the Class B private range. Answer E is correct, as this falls within the
Class C private range. Answer B is incorrect; this address does not fall
within the private IP address range. Answer D is incorrect. This address
does not fall within the private IP address range.
43.
Answers B and E are correct. Answer B will provide a 254-host network
within the private address range. Answer E is correct. Answer E will
provide a 254-host network within the private address range. Answer A
is incorrect. This will not provide enough hosts and is not within the
private address range. Answer C is incorrect. It does not fall within the
private address range. Answer D is incorrect; this network does not
provide enough hosts.
44.
Answers A, B, and D are correct. Answer A is correct. It represents a
network broadcast address and hence cannot be used. Answer B is
correct. It represents a network address and hence cannot be used.
Answer D is correct. Answer D represents a network address given this
particular subnet mask. Answer C is incorrect. This host address can be
used given this subnet mask. Answer E is incorrect. This host address
can be used given this subnet mask.
45.
Answers A, B, and E are correct. Answer A is correct. It is a standard
255.255.255.0 network; hence .0 and .255 are off limits. Answer B is
correct. It is a 255.255.240.0 network; hence a range of addresses will
be off limits, including 224.0 and 240.0. Answer E is correct. It is a
255.255.248.0, which makes 232.0, 240.0, 248.0 all network addresses.
Answer C is incorrect. It is a 255.255.192.0 network; hence 224.0 will
not represent a network address but a host address. Answer D is
incorrect. It is a 255.255.224.0 network; hence 240.0 will be an
addressable host.
46.
Answers A and B are correct. Answer A is correct. If the subnet mask
were incorrectly set (for example, 255.255.0.0 rather than
255.255.255.0), host ALPHA could have trouble determining which
traffic to send to the default gateway and which traffic is on the same
subnet. Answer B is correct. If the default gateway is incorrectly set,
traffic destined for remote networks will not be forwarded to those
networks. Answer C is incorrect. If two hosts had the same IP address,
neither would be able to receive traffic. Answer D is incorrect. DNS is
irrelevant in this situation.
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47.
Answers D and E are correct. Answer D is correct. In this situation, you
are able to ping your router, which indicates that it has not failed. The
inability to ping the ISP's router suggests that either it or the ISDN line
connecting your router to the ISP's router may have failed. Answer E is
correct. The inability to ping the ISP's router suggests that either it or
the ISDN line connecting your router to the ISP's router may have
failed. Answer A is incorrect. If your UTP cable had failed, you would
not be able to ping your router. Answer B is incorrect. If your switch had
failed, you would be unable to ping your router. Answer C is incorrect,
as you are able to ping the router.
48.
Answer C is correct. Access lists are processed sequentially. Once a
packet matches a line of the access list, the access list is no longer
processed. Because line three has a mask of 0.255.255.255, it allows
all traffic from hosts in the 10.x.x.x range to pass through. The fourth
and fifth lines of the access list will not be processed. Answer A is
incorrect. There is an implicit deny at the end of all access lists. Answer
B is incorrect; line three is where the problem in this list lies. Answer D
is incorrect, as line one only allows traffic starting with 10.20.x.x, rather
than 10.x.x.x as suggested in the answer.
49.
Answer D is correct. None of the lines of the access list directly
influence traffic on port 80 from 10.40.22.23 to 192.168.10.22. For this
reason, the implicit deny at the end of all access lists blocks this traffic.
Answer A is incorrect. Although answer A is factually true, it does not
explain why the Web server is unable to be accessed. Answer B is
incorrect. The third line does not address hosts on the 10.40.x.x
network. Answer C is incorrect. The first line of the access list does not
address hosts on the 10.40.x.x network.
50.
Answer B is correct. The show process command will display the
processor utilization over the last five seconds, last minute, and last five
minutes. This will give an overview figure of how much work the
processor is doing at any point in time. Cisco recommends avoiding
sustained processor usage exceeding 65%. Answer A is incorrect; this
command will not provide the desired output. Answer C is incorrect; this
command will not provide the desired output. Answer D is incorrect; this
command will not provide the desired output.
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51.
Answer A and D are correct. Answer A is correct. When PAP is used,
the username and password are transmitted without encryption from the
dialing router. Answer D is correct. When CHAP is used, a challenge
which includes a random number is sent from the dialed to router. This
random number is input into an MD5 algorithm to provide the encryption
key with which to send authentication information between routers.
Answer B is incorrect; CHAP uses encryption. Answer C is incorrect; no
such challenge occurs when PAP is used over a WAN connection.
52.
Answers A and C are correct. STP works by locking down all but one
active path between any two collision domains on a switch-based LAN.
Without this happening, frames could bounce indefinitely from switch to
switch, taking a different path back and forth as they attempt to reach
their destination. This would render such a network inoperable. Answer
B is incorrect; only one path can exist. Answer D is incorrect; STP stops
frames from looping indefinitely.
53.
Answers A, C, D, and E are correct. Only switch BETA will have all
ports set to the forwarding state by STP, as it has been elected the root
bridge. The ports on the other switches which have the lowest cost to
BETA will be set to the forwarding state also. Ports connected to other
switches will be set to the blocking state to stop redundant pathways to
BETA existing. If the link between BETA and another switch is broken,
STP will re-converge the network in such a way as all switches will
again be able to communicate with each other without generating
switching loops. Answer B is incorrect as all ports on BETA will transmit
frames received from other ports and forward received frames as it is
the root bridge.
54.
Answer A is correct. Spanning tree information for VLAN 2 can be
shown using the command
show spantree 2
Answer B is incorrect. The command show spantree 1 will show the
spanning tree information for VLAN 1. Answer C is incorrect. show trunk
will show the trunking information on the switch. Answer D is incorrect;
show cdp neighbors will display information about the CDP neighbors of
the switch. Answer E is incorrect. show config vlan 2 will return an error.
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55.
Answer B is correct. The show spantree statistics command will display
the spanning tree protocol BPDU communication statistics. Answer A is
incorrect. This is not a legitimate switch command. Answer C is
incorrect; this is not a legitimate switch command. Answer D is
incorrect; this is not a legitimate switch command. Answer E is
incorrect. Answer E will only show basic information about the spanning
tree protocol and does not include detailed information such as BPDU
statistics.
56.
Answer C is correct. The reason why LAN B will often outperform LAN
A is that in a switched environment, Unicast traffic is transmitted only to
the destination host. Where all hosts are connected to a hub, they will
all receive Unicast traffic, whether it is directed to them or not. When
one host is transmitting to another host on a switched network, other
hosts on the network are also free to start communication. On a
network where all hosts are connected via hub, all hosts must wait until
a single host making a Unicast transmission finishes that transmission
before initiating their own. Answer A is incorrect, as LAN B will always
out perform LAN A. Answer B is incorrect. Broadcast traffic on LAN B
will reach every host. Answer D is incorrect. Unicast traffic on LAN B
will only reach its intended destination host.
57.
Answer B is correct. Of the protocols listed, only BGP qualifies as an
exterior routing protocol. Exterior routing protocols are used between
routers that are not part of the same networks: for example, a router on
an ISP's network talking to an upstream provider. Exterior routing
protocols deal with the network borders, hence Border Gateway
Protocol. Answer A is incorrect. RIPv2 is an interior routing protocol.
Answer C is incorrect. IGRP is an interior routing protocol. Answer D is
incorrect. EIGRP is an interior routing protocol. Answer E is incorrect.
OSPF is an interior routing protocol.
58.
Answers A, C, D, and E are correct. RIPv2, IGRP, EIGRP, and OSPF
are all interior routing protocols. Interior routing protocols are used on
networks where each of the routers on the network is within the control
of a single organization. Answer B is incorrect. BGP is an exterior
routing protocol.
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59.
Answer B is correct. The maximum routing metric value of the RIP (and
RIPv2) routing protocol is 15 hops. A route with 16 hops is considered
of infinite length. Answer A is incorrect; the maximum routing metric is
15 hops. Answer C is incorrect; the maximum routing metric is 15 hops.
Answer D is incorrect; the maximum routing metric is 15 hops. Answer
E is incorrect; the maximum routing metric is 15 hops. Answer F is
incorrect; the maximum routing metric is 15 hops.
60.
Answers A, B, C, D, and E are correct. IGRP uses bandwidth, delay,
load, reliability, and MTU to generate route metric values. By default,
IGRP uses delay and bandwidth in route selection but these other
factors can influence the value. Answer F is incorrect; IOS version has
no influence on routing metric.
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Chapter 13.
Sample Exam 640-801
1.
You are designing a simple network for a small publishing company.
The company has a single two-story building that houses all 44
employees. The company wishes to be connected to the Internet and
an ISDN BRI link will be installed in the coming weeks. The company is
using an off-site hosting company to host the corporate Web site. There
are five servers located on site, two of which are used for sharing files
and printers to the employees, one is used for email, one runs a
database server, and the other authenticates logins. All employees
have workstations or laptops. The company expects to have 10% more
employees within the next two years. Which of the following design
decisions would you recommend given this information? (Select two
answers, each forms a part of the solution.)
A. Purchase four 12-port hubs. Uplink three of the hubs to the fourth.
Connect the workstations, laptops, and servers to the hubs.
B. Purchase two 24-port Cisco switches with two uplink ports. Uplink
the first switch to the second. Connect the workstations, laptops, and
servers to the switches.
C. Purchase a single 48-port Cisco switch. Connect the ISDN line to the
switch's uplink port. Connect the workstations, laptops, and servers to
the switch.
D. Purchase a single 48-port Cisco switch and a 12-port switch. Use the
uplink ports on the switches to connect them together. Connect the
workstations, laptops, and servers to the switch.
E. Purchase a Cisco router. Connect the ISDN line to the router.
Connect the router to the 48-port switch.
F. Purchase a Cisco router. Connect the ISDN line to the router.
Connect the router to one of the 24 port switches.
G. Purchase a Cisco router. Connect the ISDN line to the router.
Connect the router to the 12-port hub that has the other three uplinked
to it.
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2.
You have been asked to design a simple LAN for an accounting
company. The accounting company is located in an office park. There
are 120 employees located in three buildings. Each employee has a
computer. The buildings are each approximately 180 meters from each
other. The buildings are named Building A, Building B, and Building C.
The largest number of employees, 50, is in Building B. The smallest
number, 30, is located in Building A. You wish to network all of these
buildings together, provide access for all employees to the network, and
connect them to an ISDN PRI line running from Building A to the
company's ISP. Which of the following schemes will best do this?
A. Purchase 10 12-port Cisco switches. Place 2 in Building C, 5 in
Building B, and 3 in Building C. Use CAT 5 UTP cable to connect all of
the hosts to the switches. Use CAT 5 UTP to connect the uplink ports of
one of the switches in each building to the switches in the other two.
Purchase a Cisco router and install it in Building A. Connect the router
to the ISDN line as well as one of the switches.
B. Purchase 3 48-port Cisco switches and a single 12-port Cisco switch.
Place one 48-port switch in each building. Place the 12-port switch in
Building B. Use CAT 5 UTP to connect all of the hosts to the switches.
Use CAT 5 UTP to connect the uplink ports on one of the switches in
each building to the switches in the other two. Use the uplink port on the
12-port switch to connect it to that building's 48-port switch. Purchase a
Cisco router and install it in Building A. Connect the router to the ISDN
line as well as the 48-port switch.
C. Purchase 3 48-port Cisco switches. Place one in each building. Use
CAT 5 UTP to connect all of the hosts to the switches. Use CAT 5 UTP
to connect the uplink ports on one of the switches in each building to
the switches in the other two. Purchase a Cisco router and install it in
Building A. Connect the router to the ISDN line as well as the 48-port
switch.
D. Purchase 3 48-port Cisco switches and a single 12-port Cisco
switch. Place one 48-port switch in each building. Place the 12-port
switch in Building B. Use CAT 5 UTP to connect all of the hosts to the
switches. Use CAT 5 UTP with repeaters (no segment more than 95
meters) to connect the uplink ports on one of the switches in each
building to the switches in the other two. Use the uplink port on the 12port switch to connect it to that building's 48-port switch. Purchase a
Cisco router and install it in Building A. Connect the router to the ISDN
line as well as the 48-port switch.
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3.
Rooslan has been allocated the network range 192.168.20.0 /24. From
this range he needs to create four subnets. The first subnet must
support 90 hosts. The second must support 40 hosts. The third must
support 30 hosts, and the final network must support 24 hosts. Which of
the following schemes will meet Rooslan's needs?
A. First: 192.168.20.0 /25, Second: 192.168.20.128 /26, Third:
192.168.20.192 /27, Fourth: 192.168.20.240 /28
B. First: 192.168.20.0 /25, Second: 192.168.20.128 /26, Third:
192.168.20.192 /27, Fourth: 192.168.20.224 /27
C. First: 192.168.20.0 /26, Second: 192.168.20.64 /26, Third:
192.168.20.192 /27, Fourth: 192.168.20.224 /27
D. First: 192.168.20.0 /25, Second: 192.168.20.128 /26, Third:
192.168.20.192 /28, Fourth: 192.168.20.240 /28
4.
Which of the following /24 subnets can be supernetted into a larger
network?
A. 10.10.20.0 /24 and 10.10.21.0 /24 into 10.10.20.0 /23
B. 10.10.21.0 /24 and 10.10.22.0 /24 into 10.10.21.0 /23
C. 10.10.130.0 /24, 10.10.131.0 /24, 10.10.132.0 /24, and 10.10.133.0
/24 into 10.10.130.0 /22
D. 10.10.164.0 /24, 10.10.165.0 /24, 10.10.166.0 /24, and 10.10.167.0
/24 into 10.10.165.0 /22
5.
You are trying to select a routing protocol to use on a large
internetwork. 60% of the routers on the network are Cisco systems
running IOS, and 40% are manufactured by other vendors. Which of the
following routing protocols are unlikely to be supported by the 40% of
routers manufactured by other vendors? (Select all that apply.)
A. IGRP
B. RIP
C. RIPv2
D. OSPF
E. BGP
F. EIGRP
6.
There are 326 routers used in a network for a government department.
Some routes are 25 hops in diameter. Which of the following routing
protocols could not fully map this network?
A. OSPF
B. IGRP
C. RIPv2
D. EIGRP
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7.
You are designing a network for a small bank that has branch offices
spread all across the state. There are seven branch offices and a
central office. Four of the branch offices have a single TCP/IP subnet,
and three of the branch offices have two TCP/IP subnets. Each branch
office is connected via ISDN line to the central office. What is the
minimum number of routers that will be required for the branch offices if
VLANs are not used for branch office hosts to communicate with the
central office?
A. 6
B. 7
C. 8
D. 9
8.
You are designing a network for an insurance company that has offices
in several capital cities around the country. There is a single head office
and six branch offices. You are going to use ISDN BRI leased lines to
connect each office to the head office. You also want to configure the
network so that it will still operate if a single ISDN BRI line fails. If this
occurs, data transmission should be sent via an ISDN BRI line to
another branch office, which will then forward the data to the head
office. How many ISDN lines will be required to implement such a
network?
A. 6
B. 11
C. 9
D. 30
9.
You wish to write an access list that allows access from hosts with IP
addresses in the range 10.10.0.0 through to 10.10.255.255. Which of
the following access lists will achieve this goal?
A. ACCESS LIST 1 PERMIT 10.10.0.0 255.255.255.0
B. ACCESS LIST 201 PERMIT 10.10.0.0 255.255.255.0
C. ACCESS LIST 1 PERMIT 10.10.0.0 255.255.0.0
D. ACCESS LIST 201 PERMIT 10.10.0.0 255.255.0.0
E. ACCESS LIST 1 PERMIT 10.10.0.0 0.0.255.255
F. ACCESS LIST 201 PERMIT 10.10.0.0 255.255.0.0
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10.
You have the following access list:
ACCESS LIST 1 DENY 10.100.45.0 0.0.0.127
ACCESS LIST 1 PERMIT 10.100.20.0 0.0.255.255
Interface e0 is connected to the internal network, which includes the IP
range 10.100.0.0 /16. Access list 1 is applied inbound on interface e0.
Interface s1 is connected to internal network 10.200.0.0 /16. Which of
the following host addresses will not be able to send traffic through the
router to the network that is connected to interface s1? (Select all that
apply.)
A. 10.100.240.223
B. 10.100.20.132
C. 10.100.45.223
D. 10.100.45.25
E. 10.100.45.118
11.
One of your clients has asked you to implement a WAN service that will
be relatively inexpensive, provide extra data transfer speed if required,
and allow new sites to be added to the network quickly. Which of the
following WAN technologies will allow this?
A. Leased Line—HDLC
B. Leased Line—LAPB
C. Packet Switched—Frame Relay
D. Packet Switched—ATM
12.
Your company has decided to go with a leased-line solution in
provisioning WAN connections. They want to use the default leased-line
protocol for Cisco systems because Cisco manufactures all of the
routers and switches on the corporate network. When on a leased-line
WAN service, which of the following data-link protocols is the default
used by Cisco routers?
A. SLIP
B. PPP
C. HDLC
D. LAPB
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13.
You are working on a network that only supports RIPv1. Which of the
following IOS command sequences will force a Cisco router named
router to only send and receive RIPv1, rather than RIPv1 and RIPv2
routing updates?
A. router#configure terminal
router(config)#router rip
router(config-router)#version 1
router(config-router)#end
B. router#configure terminal
router(config)#interface e0
router(config-if)#router ripv1
C. router#configure terminal
router(config)#router ripv1
D. router#configure terminal
router(config)#interface e0
router(config-if)#set rip version 1
14.
You are adding a router to a network that is entirely made up of Cisco
equipment. The routing protocol in use is EIGRP, which is a proprietary
protocol from Cisco. The EIGRP's AS (Autonomous System) number is
77. Which of the following IOS command sequences will configure
EIGRP with an AS of 77 for the network 10.10.50.0? (Assume that the
appropriate interface has already been configured.)
A. NEWROUTER(config)#router rip 77
NEWROUTER(config-router)#network 10.50.10.0
NEWROUTER(config-router)#end
B. NEWROUTER(config)#router eigrp 77
NEWROUTER(config-router)#network 10.50.10.0
NEWROUTER(config-router)#end
C. NEWROUTER(config)#router eigrp 77
NEWROUTER(config-router)#network 10.10.50.0
NEWROUTER(config-router)#end
D. NEWROUTER(config)#router eigrp 66
NEWROUTER(config-router)#network 10.50.10.0
NEWROUTER(config-router)#end
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15.
Which of the following sets of IOS commands will set the IP address of
router ODLT1's e0 interface to 10.10.40.1 /27, the address of the s1
interface to 10.10.41.1 /29, and the address of the s2 interface to
10.10.40.33 /28? (Select all that apply.)
A. ODLT1(config)#interface e0
ODLT1(config-if)#ip address 10.10.40.1 255.255.240.0
ODLT1(config-if)#no shut
B. ODLT1(config)#interface e0
ODLT1(config-if)#ip address 10.10.40.1255.255.224.0
ODLT1(config-if)#no shut
C. ODLT1(config)#interface s1
ODLT1(config-if)#ip address 10.10.41.1 255.255.240.0
ODLT1(config-if)#no shut
D. ODLT1(config)#interface s2
ODLT1(config-if)#ip address 10.10.40.33 255.255.248.0
ODLT1(config-if)#no shut
E. ODLT1(config)#interface s2
ODLT1(config-if)#ip address 10.10.40.33 255.255.240.0
ODLT1(config-if)#no shut
F. ODLT1(config)#interface s1
ODLT1(config-if)#ip address 10.10.41.1 255.255.248.0
ODLT1(config-if)#no shut
16.
You want to configure the e0 interface of a router with the IP address
10.10.10.31. Which of the following steps taken in IOS will apply this
address with a subnet mask, thereby making it addressable on the
network to interface e0?
A. ROUTER(config)#interface e0
ROUTER(config-if)#ip address 10.10.10.31 255.255.255.0
ROUTER(config-if)#no shut
B. ROUTER(config)#interface e0
ROUTER(config-if)#ip address 10.10.10.31 255.255.255.192
ROUTER(config-if)#no shut
C. ROUTER(config)#interface e0
ROUTER(config-if)#ip address 10.10.10.31 255.255.255.224
ROUTER(config-if)#no shut
D. ROUTER(config)#interface e0
ROUTER(config-if)#ip address 10.10.10.31 255.255.255.240
ROUTER(config-if)#no shut
E. ROUTER(config)#interface e0
ROUTER(config-if)#ip address 10.10.10.31 255.255.255.248
ROUTER(config-if)#no shut
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17.
Which of the following protocols does Cisco recommend that you use to
support a router to act as a terminal server to manage other routers?
A. RADIUS
B. TACACS+
C. IGRP
D. OSPF
18.
What is the maximum number of VLANs that have a separate spanning
tree supported by Catalyst 1900 switches?
A. 8
B. 16
C. 32
D. 64
E. 128
19.
Which of the following IOS commands issued on a Cisco Catalyst 1900
switch will display the VLAN membership of each of the ports?
A. list ports
B. list VLAN
C. show VLAN-membership
D. VLAN-membership
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20.
You are designing a LAN for a large manufacturing company's
production site. There is a single factory building that is 200 meters
long. The first 50 meters are taken up with office space for the
administrative staff. The rest of the factory is filled with large equipment
that occasionally generates electrical interference. There are 50
workstations and three servers located in the administrative area.
Throughout the rest of the factory there are 20 workstations. All of these
workstations are located between 120 and 180 meters from the
administrative area. All need to be networked to each other. You have
the following equipment available:
80 lengths of UTP cable (of whatever is required length)
25 lengths of STP cable (of whatever is required length)
1 48-port Cisco Catalyst switch
2 24-port Cisco Catalyst switches
2 repeaters
What should you do to provide connectivity to all of these hosts given
the available equipment?
A. Place the 48-port and one 24-port switch in the administration area.
Connect them to each other using a single UTP cable. Connect all of
the hosts in the administration area to these two switches with lengths
of UTP cable. Place the second 24-port catalyst switch in a safe
position 150 meters from the administration area. Connect two 90-meter
lengths of UTP cable together with one of the repeaters and use this
longer cable to connect the 48-port switch with the 24-port switch out in
the factory. Use 20 lengths of STP cable to connect the hosts on the
factory floor to the switch.
B. Place the 48-port and one 24-port switch in the administration area.
Connect them to each other using a single STP cable. Connect all of
the hosts in the administration area to these two switches with lengths
of UTP cable. Place the second 24-port catalyst switch in a safe
position 150 meters from the administration area. Connect two 90-meter
lengths of STP cable together with one of the repeaters and use this
longer cable to connect the 48-port switch with the 24-port switch out in
the factory. Use 20 lengths of UTP cable to connect the hosts on the
factory floor to the switch.
C. Place both 24-port switches in the administration area. Connect them
to each other using a single UTP cable. Use lengths of UTP cable to
connect all of the hosts in the administration area to these two switches.
Place the 48-port catalyst switch in a safe position 150 meters from the
administration area. Connect two 90-meter lengths of STP cable
together with one of the repeaters and use this longer cable to connect
one of the 24-port switches with the 48-port switch out in the factory.
Use 20 lengths of UTP cable to connect the hosts on the factory floor to
the switch.
D. Place the 48-port and one 24 port-switch in the administration area.
Connect them to each other using a single UTP cable. Use lengths of
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UTP cable to connect all of the hosts in the administration area to these
two switches. Place the second 24-port catalyst switch in a safe position
150 meters from the administration area. Connect two 90-meter lengths
of STP cable together with one of the repeaters and use this longer
cable to connect the 48-port switch with the 24-port switch that is
located out in the factory. Use 20 lengths of STP cable to connect the
hosts on the factory floor to the switch.
21.
You have been asked to help with a local school's LAN that has
become bogged down due to heavy data traffic. The LAN currently has
220 hosts on a single TCP/IP subnet. The school administration does
not want this network resubnetted. Which of the following devices can
be implemented on the network to reduce the amount of unicast traffic
on each segment of the network? (Select all that apply.)
A. Bridge
B. Switch
C. Router
D. Repeater
22.
You wish to configure a switch so that it examines each frame for errors
in its entirety before forwarding it on to its destination. For which of the
following switching methods should a Catalyst 1900 switch be
configured to perform this function?
A. Fragment-free switching
B. Store-and-forward switching
C. Cut-through switching
D. Basic switching
23.
You wish to configure a Cisco Catalyst switch to use a method of
switching that will perform some error correction on frames transmitted
across the network, but that the latency caused by that error correction
will not increase with the size of the frame. Which of the following
switching methods should you implement?
A. Fragment-free switching
B. Store-and-forward switching
C. Cut-through switching
D. Basic switching
24.
Which of the following IOS commands will back up the starting
configuration to a TFTP server located on IP address 10.10.10.99?
A. backup start-config tftp 10.10.10.99
B. backup running-config tftp 10.10.10.99
C. copy tftp start-config
D. copy start-config tftp
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25.
Which of the following commands can be used to copy the startup
configuration to the running configuration on a switch?
A. copy run start
B. copy start run
C. overwrite run start
D. overwrite start run
26.
Which of the following commands will set a router's host name to
PHOENIX?
A. hostname PHOENIX
B. set name PHOENIX
C. configure name PHOENIX
D. apply name PHOENIX
27.
Which of the following IOS command sequences will set the enable
password to CAPRICORNUS and the console password to AQUILA on
router PHOENIX?
A. PHOENIX(config)#enable password CAPRICORNUS
PHOENIX(config)#line con 0
PHOENIX(config-line)#password AQUILA
B. PHOENIX(config)#enable password
PHOENIX(config)#set password CAPRICORNUS
PHOENIX(config)#line con 0
PHOENIX(config-line)#password AQUILA
C. PHOENIX(config)#enable password CAPRICORNUS
PHOENIX(config)#line vty 0 4
PHOENIX(config-line)#password AQUILA
D. PHOENIX(config)#configure password CAPRICORNUS
PHOENIX(config)#line con 0
PHOENIX(config-line)#enable password AQUILA
28.
Which of the following settings are the defaults on a Catalyst 1900
switch when it is first powered on?
A. CDP: Enabled
B. Console Password: CISCO
C. Spanning Tree: Disabled
D. Switching Mode: Store and Forward
E. 10BaseT port: Full Duplex
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29.
You are configuring a Cisco Catalyst 1900 switch from the command
line. Which of the following groups of commands will set the IP of the
switch to 10.10.10.54 /29 and the default gateway to 10.10.10.49?
A. switch# configure terminal
switch(config)#ip address 10.10.10.54 255.255.255.240
switch(config)#ip default-gateway 10.10.10.54
B. switch# configure terminal
switch(config)#ip address 10.10.10.54 255.255.255.248
switch(config)#ip default-gateway 10.10.10.54
C. switch# configure terminal
switch(config)#ip address 10.10.10.49 255.255.255.240
switch(config)#ip default-gateway 10.10.10.54
D. switch# configure terminal
switch(config)#ip address 10.10.10.54 255.255.255.240|
switch(config)#ip default-gateway 10.10.10.49
E. switch# configure terminal
switch(config)#ip address 10.10.10.54 255.255.255.248
switch(config)#ip default-gateway 10.10.10.49
30.
Router Alpha's E0 interface is connected to the Internet. Router Alpha's
S1 interface is connected to the internal network that encompasses 30
/24 bit networks from 10.10.10.0 /24 through to 10.10.40.0 /24. You
have two goals. First, you want to stop traffic from network 10.10.36.0
/24 from reaching the Internet. Second, you only want traffic from the
network 192.168.24.0 /24 to reach the internal network from the
Internet. You have the following access lists:
ACCESS LIST 1 PERMIT 192.168.24.0 255.255.255.0
ACCESS LIST 2 PERMIT 192.168.24.0 0.0.0.255
ACCESS LIST 3 DENY 10.10.36.0 255.255.255.0
ACCESS LIST 4 DENY 10.10.36.0 0.0.0.255
Which of the following describes how these access lists can be applied
to meet your two goals?
A. Apply access list 1 to interface e0 out; apply access list 3 to interface
s1 in.
B. Apply access list 1 to interface e0 in; apply access list 3 to interface
s1 in.
C. Apply access list 2 to interface e0 out; apply access list 4 to interface
s1 in.
D. Apply access list 2 to interface e0 in; apply access list 4 to interface
s1 in.
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31.
You wish to block users from the network 192.168.20.0 /24, which is a
network connected to interface e0, from using the FTP protocol to
connect to host 192.168.40.24 on the network that is connected to
interface s1. These are the only two configured interfaces on the router,
and no other path exists between the networks. Which of the following
will achieve this goal?
A. Create an access list: access-list 101 deny tcp 192.168.20.0
255.255.255.0 192.168.40.24 eq ftp and apply this access list to
incoming traffic on interface e0.
B. Create an access list: access-list 101 deny tcp 192.168.20.0
0.0.0.255 192.168.40.24 eq ftp and apply this access list to outgoing
traffic on interface s1.
C. Create an access list: access-list 101 deny tcp 192.168.20.0
0.0.0.255 192.168.40.24 eq ftp and apply this access list to outgoing
traffic on interface e0.
D. Create an access list: access-list 101 deny tcp 192.168.20.0
255.255.255.0 192.168.40.24 eq ftp and apply this access list to
incoming traffic on interface s1.
E. None of the above.
32.
You wish to configure interface s0, which will host a frame relay
connection to a remote office, to send keepalive packets through the
PVC every 20 seconds. Keepalive packets verify that the path is still
available. Which of the following IOS sequences will achieve this goal?
A. WANROUTE(config)#interface s0
WANROUTE(config-if)#encapsulation ppp
WANROUTE(config-if)#keepalive 20
WANROUTE(config-if)#end
B. WANROUTE(config)#interface s1
WANROUTE(config-if)#encapsulation frame-relay
WANROUTE(config-if)#keepalive 20
WANROUTE(config-if)#end
C. WANROUTE(config)#interface s0
WANROUTE(config-if)#encapsulation ppp
WANROUTE(config-if)#keepalive 5
WANROUTE(config-if)#end
D. WANROUTE(config)#interface s0
WANROUTE(config-if)#encapsulation frame-relay
WANROUTE(config-if)#keepalive 20
WANROUTE(config-if)#end
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33.
Which layer of the OSI model represents where you would begin
troubleshooting problems with frames?
A. Layer 1
B. Layer 2
C. Layer 3
D. Layer 4
34.
Which layer of the conceptual OSI model represents where you would
begin troubleshooting problems with IP addressing?
A. Layer 1
B. Layer 2
C. Layer 3
D. Layer 4
35.
Your local area network is suffering from frequent overloads of
broadcast traffic. Which of the following hardware devices could not be
used to reduce the amount of broadcast traffic on the LAN? (Select
two.)
A. Cisco Catalyst 1900 switch
B. Cisco 2500 series router
C. Repeater
D. Hub
36.
You wish to decrease the amount of time that an RIP network takes to
converge after a topology change. You want the update period to be 10
seconds. You also want to set the invalid route timer to 100 seconds,
the hold-down timer to 100 seconds, and the flush timer to 110
seconds. Which of the following IOS commands, entered after router
rip, will enable you to achieve this goal?
A. timers basic 10 100 100 110
B. set rip timers 20 100 100 110
C. configure rip timers 20 100 100 110
D. routing update 10 100 100 95
37.
You have inherited a /24 network that has been separated into several
/29 networks. The original network was 192.168.10.0 /24. You are
currently looking at a list of IP addresses that can be assigned to router
interfaces. Which of the following IP addresses can be assigned to
router interfaces given this networking scheme?
A. 192.168.10.15
B. 192.168.10.223
C. 192.168.10.184
D. 192.168.10.153
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38.
Your national company uses the 192.168.0.0 private address space.
Your state network has been assigned the 192.168.100.0 /24 and
192.168.101.0 /24 address space. You have subnetted the two address
spaces into a total of 16 equal-sized networks. Which of the following IP
addresses cannot be assigned to hosts on the networks within your
state?
A. 192.168.100.31
B. 192.168.101.63
C. 192.168.101.203
D. 192.168.100.227
E. 192.168.100.129
39.
Your network consists of four switches, two repeaters, a single router,
two subnets, and 160 hosts. Switches one and two are on subnet
192.168.10.0 /25, and switches three and four are on subnet
192.168.10.128 /25. Hosts 192.168.10.5 through 192.168.10.45 are
connected to switch one. Hosts 192.168.10.46 through 192.168.10.86
are connected to switch two. Two segments of UTP, connected via a
repeater, connect switch one to switch two. Hosts 192.168.10.130
through hosts 192.168.10.170 are connected to switch three. Hosts
192.168.10.171 through hosts 192.168.10.211 are connected to switch
four. Switch three is connected to switch four via two segments of UTP
cable connected together via a repeater. Switch four is connected via
UTP to the router. Switch one is connected to the router. Host
192.168.10.50 cannot ping host 192.168.10.165. Host 192.168.10.70
can ping host 192.168.10.200. Assuming all of the hosts work, which of
the following devices could be faulty? (Select all that apply.)
A. The router
B. Switch three
C. Switch four
D. Switch one
E. Switch two
F. The repeater between switches one and two
G. The repeater between switches three and four
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40.
You have six switches, 120 hosts, three networks, and one router. Your
network configuration can be summarized as follows:
Switches Alpha and Beta service hosts on Network 10.10.10.0 /24. This
network is connected to interface e0 on the router. The hosts on switch
Alpha have IP addresses between 10.10.10.10 and 10.10.10.30. The
hosts on switch Beta have IP addresses between 10.10.10.50 and
10.10.10.70. Switch Alpha is connected to switch Beta. Switch Beta is
connected to the router.
Switches Gamma and Delta service hosts on Network 10.10.20.0 /24.
This network is connected to interface s1 on the router. The hosts on
switch Gamma have IP addresses between 10.10.20.10 and
10.10.20.30. The hosts on switch Delta have IP addresses between
10.10.20.50 and 10.10.20.70. Switch Gamma is connected to switch
Delta. Switch Delta is connected to the router.
Switches Epsilon and Omega service hosts on network 10.10.30.0 /24.
This network is connected to interface s2 on the router. The hosts on
switch Epsilon have IP addresses between 10.10.30.10 and
10.10.30.30. The hosts on switch Omega have IP addresses between
10.10.30.50 and 10.10.30.70. Switch Epsilon is connected to switch
Omega. Switch Omega is connected to the router.
See Figure 1(below) for a diagram.
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Until yesterday, all hosts were able to communicate with each another.
This morning your users have reported some problems. You perform
some testing and come up with the following results:
Host 10.10.20.24 can ping host 10.10.20.58
Host 10.10.10.14 can ping host 10.10.30.68
Host 10.10.30.27 can ping host 10.10.10.57
Host 10.10.30.65 cannot ping host 10.10.20.51
Given this information, and assuming that all hosts are functioning
properly, which of the following networks might have caused the
problem?
A. Interface e0 of the router is down
B. Interface s1 of the router is down
C. Interface s2 of the router is down
D. Switch Delta is down
E. Switch Omega is down
F. Switch Beta is down
41.
You have the following access list:
ACCESS LIST 1 PERMIT 10.10.0.0 0.0.255.255
ACCESS LIST 1 DENY 10.10.100.0 0.0.0.255
ACCESS LIST 1 DENY 10.10.130.0 255.255.255.0
ACCESS LIST 1 DENY 10.10.150.0 0.0.0.255
You want to make sure that traffic from the networks 10.10.100.0 /24
and 10.10.150.0 /24 are blocked, but still allow all other traffic from the
10.10.0.0 /16 network. How should you modify the access list? (Select
two.)
A. Delete line three of the access list.
B. Modify line four of the access list to ACCESS LIST 1 DENY
10.10.150.0 255.255.255.0.
C. Modify line three of the access list to ACCESS LIST 1 DENY
10.10.130.0 0.0.0.255.
D. Move line one of the access list to the end of the access list.
E. Modify line two of the access list to ACCESS LIST 1 DENY
10.10.100.0 255.255.255.0.
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42.
You have the following access list:
ACCESS LIST 101 deny tcp any host 192.168.10.21 eq 80
ACCESS LIST 101 deny tcp 192.168.20.0 0.0.0.255 eq telnet
ACCESS LIST 101 deny tcp 192.168.0.0 0.0.255.255 192.168.10.22 eq
ftp
ACCESS LIST 101 allow tcp 192.168.44.0 0.0.0.255 192.168.10.22 eq
ftp
You want to achieve the following:
Block telnet access to any host on the 192.168.10.0 /24 network from
the 192.168.20.0 /24 network.
Allow all hosts access to the Web server on host 192.168.10.21.
Allow hosts on network 192.168.44.0 /24 ftp access to host
192.168.10.22 but block ftp access to this host from other networks in
the 192.168.0.0 /24 range.
Which of the following modifications do not have to be made to the
access list? (Select all that apply.)
A. Change line one to ACCESS LIST 101 allow tcp any host
192.168.10.21 eq 80.
B. Change line two to ACCESS LIST 101 deny tcp 192.168.20.0
0.0.0.255 192.168.10.0 0.0.0.255 eq telnet.
C. Rearrange the access list so that line 4 is above line 3.
D. Change line one to ACCESS LIST 101 allow tcp any host
192.168.10.21 0.0.255.255 eq 80.
E. Change line two to ACCESS LIST 101 allow tcp 192.168.20.0
0.0.0.255 192.168.10.0 0.0.0.255 eq telnet.
43.
Which of the following best describes how information progresses up
the OSI model from Layer 1 to Layer 5?
A. Bits -> Packets -> Frames -> Datagrams -> Segments
B. Bits -> Datagrams -> Frames -> Packets -> Segments
C. Bits -> Frames -> Packets -> Segments -> Datagrams
D. Bits -> Frames -> Packets -> Datagrams -> Segments
44.
Which of the following correctly map the appropriate layer with the
description of information that is transmitted at that layer? (Select all
that apply.)
A. Layer 1 = Bits
B. Layer 2 = Packets
C. Layer 3 = Frames
D. Layer 4 = Segments
E. Layer 5 = Datagrams
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45.
Which of the following best describes the spanning tree process?
A. Spanning tree creates a series of redundant links between switches.
B. Spanning tree creates a loop network so that data may reach its
destination via multiple paths.
C. Spanning tree blocks of ports on redundant links so that there is only
one path through the LAN from one switch to the next.
D. Spanning tree creates multiple links so that bandwidth can be
aggregated creating faster transfer speeds.
46.
How many STP root bridges are on a network that contains two TCP/IP
subnets separated by a Cisco router, with each subnet hosting six
Cisco Catalyst 1900 switches?
A. 1
B. 2
C. 3
D. 4
47.
Which of the following correctly describes the difference between
broadcast, unicast, and multicast transmissions on a LAN?
A. Unicast transmissions are sent from one host to all hosts. Broadcast
transmissions are sent from all hosts to one host. Multicast
transmissions are sent from some hosts to some other hosts.
B. Unicast transmissions are sent from a single host to another single
host. Broadcast transmissions are sent from a single host to all hosts on
the LAN. Multicast transmissions are sent from a single host to a group
of hosts.
C. Unicast transmissions are sent from a single host to another single
host. Broadcast transmissions are sent from a single host to a small
group of hosts. Multicast transmissions are sent from a single host to all
hosts on the LAN.
D. Unicast transmissions are sent from a single host to a group of
hosts. Broadcast transmissions are sent from a single host to all hosts
on the LAN. Multicast transmissions are sent from a single host to
another single host.
48.
Which of the following statements is true?
A. Switches, without VLANs, reduce the size of broadcast domains.
B. Switches, without VLANs, reduce the size of unicast collision
domains.
C. Routers reduce the size of broadcast domains.
D. Switches, when configured with two or more VLANs, reduce the size
of broadcast domains.
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49.
Which of the following routing protocols are, or make use of, the
Distance Vector process?
A. RIPv2
B. OSPF
C. IGRP
D. EIGRP
50.
Which of the following routing protocols are exterior routing protocols?
A. RIPv2
B. IGRP
C. OSPF
D. BGP
51.
You want to transfer files back and forth across a network, but you are
not as concerned about error correction as you are about the speed of
the transfer. Which of the following protocols might you utilize?
A. HTTP
B. Telnet
C. TFTP
D. FTP
52.
Which of the following ports on a router can be used to initially configure
a router via a special cable to a laptop that is running appropriate
software?
A. console port
B. auxiliary port
C. UTP port
D. serial port
53.
Which of the following Router memory types stores the IOS image?
A. RAM
B. ROM
C. FLASH
D. NVRAM
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54.
You have the following access list:
ACCESS LIST 101 deny tcp 10.10.0.0 0.0.255.255 192.168.10.24 eq
ftp
ACCESS LIST 101 deny tcp 10.10.10.0 0.0.0.255 192.168.10.24 eq 80
ACCESS LIST 101 allow tcp 10.10.10.0 0.0.0.128 192.168.10.24 eq
telnet
ACCESS LIST 101 allow tcp 10.10.10.0 0.0.0.255 192.168.10.25 eq 80
ACCESS LIST 101 allow tcp 10.10.0.0 0.0.255.255 192.168.10.25 eq
ftp
Which of the following packets will be discarded while passing through
an interface that has this access list applied? (Select all that apply.)
A. FTP packets from host 10.10.234.65 to host 192.168.10.24 will be
discarded.
B. HTTP packets from host 10.10.20.0 to host 192.168.10.24 will be
discarded.
C. Telnet packets from host 10.10.10.15 to host 192.168.10.24 will be
discarded.
D. FTP packets from host 10.10.99.65 to host 192.168.10.25 will be
discarded.
E. HTTP packets from host 10.10.10.47 to host 192.168.10.24 will be
discarded.
55.
You have the following access list:
ACCESS LIST 102 deny tcp 10.50.0.0 0.0.255.255 192.168.10.24 eq
ftp
ACCESS LIST 102 deny tcp 10.60.0.128 0.0.255.127 192.168.10.24 eq
ftp
ACCESS LIST 102 deny tcp 10.70.0.0 0.0.0.255 192.168.10.24 eq ftp
ACCESS LIST 102 deny tcp 10.80.0.0 0.0.255.255 192.168.10.24 eq
ftp
ACCESS LIST 102 allow tcp 10.100.0.0 0.255.255.255 192.168.10.24
eq ftp
Which of the following FTP packets will be discarded while attempting
to travel through an interface where this access list is applied?
A. FTP packets from host 10.100.24.22 to host 192.168.10.24
B. FTP packets from host 10.51.101.223 to host 192.168.10.24
C. FTP packets from host 10.60.103.54 to host 192.168.10.24
D. FTP packets from host 10.60.94.200 to host 192.168.10.24
E. FTP packets from host 10.79.105.22 to host 192.168.10.24
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Answer Key 640-801
Answer Key
1. D and E
2. D
3. B
4. A and D
5. A and F
6. C
7. B
8. C
9. E
10. D and E
11. C
12. C
13. A
14. C
15. B, E, and F
16. A and B
17. B
18. D
19. C
20. D
21. A and B
22. B
23. A
24. D
25. B
26. A
27. A
28. A
29. E
30. D
31. B
32. D
33. B
34. C
35. C and D
36. A
37. D
38. A and B
39. B and G
40. B
41. A and D
42. D and E
43. C
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44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
A, D, and E
C and D
B
B
B, C, and D
A, C, and D
D
C
A&B
C
A, B, and E
D
1.
Answers D and E are correct. D is correct because it allows for
company growth providing 60 ports for use on the network. Once
answer D is chosen, the only one of the second parts of the solution
that mentions a 48-port switch is answer E. The router will mediate all
traffic going to networks other than that hosted in the building. Answer A
is incorrect, as not enough ports will be available for the company or its
growth projection. Answer B is incorrect, as not enough ports will be
available given the company's projected growth. Answer C is incorrect,
as not enough ports will be available given the company's projected
growth. Answer F is wrong, as it can only be true if answer B is true.
Answer G is wrong, as it depends on answer A being true.
2.
Answer D is correct. It allocates more than the correct number of ports
to each building. It also mentions utilizing repeaters to bridge the
distance between each building. Answer A is incorrect because it does
not provide enough ports for Building C (two 12-port hubs = 24 hosts;
Building C has 40 computers). Answer B is incorrect because the
distance between buildings exceeds that supported for UTP. Repeaters
are needed. Answer C is incorrect because Building B, which has 50
hosts, will not be able to connect all of them to the network. It also
suffers from the problem of not having any repeaters on the cables that
run between buildings.
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3.
Answer B is correct. In the subnetting scheme in answer B, 126 hosts
are allocated for the first network, 62 are allocated to the second, 30 are
allocated to the third, and 30 to the fourth. A quick formula for
calculating the number of hosts on a network using its CIDR (Classless
Inter Domain Routing) number (the one after the /) is (2(32-CIDR))-2.
Hence number of hosts when CIDR = 25 is (2(32-25))-2 = 126. Answer
A is incorrect because it only allocates 14 addresses for the final
network and it must support at least 24. Answer C is incorrect because
only 62 hosts are allocated for the first network and the first network
must support 90 hosts. Answer D is incorrect because only 14 hosts are
allocated to the third and 14 hosts allocated to the fourth network. The
third network must support 30 hosts and the fourth network must
support 24 hosts.
4.
Answers A and D are correct because these two networks can be
supernetted together. The secret to figuring this out is that the start of
the network must be a multiple of four. See the main text for an
overview of subnetting. Answer B is incorrect because these two
networks cannot be supernetted together; 10.10.21.0 needs to be
paired with 10.10.20.0 in a /23 network and 10.10.22.0 with 10.10.23.0.
Answer C is incorrect; 10.10.130.0 and 10.10.131.0 would be part of the
10.10.128.0 /23 network. 10.10.132.0 and 10.10.133.0 would be part of
the 10.10.132.0 /23 network.
5.
Answers A and F are correct. IGRP and EIGRP are protocols designed
and implemented by Cisco. They are not "open" standards, but
proprietary and unlikely to be used on non-Cisco equipment. Answer B
is incorrect. RIP is an open protocol and is supported by all router
manufacturers. Answer C is incorrect. RIPv2 is an open protocol and is
supported by all router manufacturers. Answer D is incorrect. OSPF is
an open protocol and is supported by all router manufacturers. Answer
E is incorrect. BGP is an open protocol and is supported by all router
manufacturers. BGP is not used on internal internetworks but is used
for routers on the larger internet.
6.
Answer C is correct. This question asks which protocols could not map
this network. RIPv2 can map routes up to 15 hops in diameter. Routes
16 hops away are considered an infinite distance away. RIPv2 would
not be able to map this network. Answer A is incorrect because OSPF
could map this network. Answer B is incorrect because IGRP could map
this network. Answer D is incorrect because EIGRP could map this
network.
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7.
Answer B is correct. At least one router per branch office is required.
Seven branch offices equals seven routers. Even if there are two
subnets, only one router is required at the branch office. Answer A is
incorrect. At least one router per branch office is required. Even if there
are two subnets, only one router is required at the branch office.
Answer C is incorrect. At least one router per branch office is required.
Even if there are two subnets, only one router is required at the branch
office. Answer D is incorrect. At least one router per branch office is
required. Even if there are two subnets, only one router is required at
the branch office.
8.
Answer C is correct. Six lines will be required. The first requirement is
one from each branch office to the head office. Each branch office can
then be paired with a partner for the sake of redundancy. This creates
three pairs and another three lines, for a total of nine lines. Answer A is
incorrect. It provides no redundancy if a single ISDN line fails. Answers
B and D are incorrect. Six lines, one from each branch office to the
head office, compose the first requirement. Each branch office can be
then paired with a partner for the sake of redundancy. This creates
three pairs and another three lines for a total of nine lines. Tolerance of
two lines failing is not required.
9.
Answer E is correct. This will allow access from 10.10.x.x, which is the
entire range that should be granted access. Answer A is incorrect
because it permits hosts from networks x.x.x.0 (where x can be
anything from 1 to 255). Answer B is incorrect. Access lists in the 200
range do not deal with TCP/IP, but protocol type codes. Answer C is
incorrect because it allows access from networks x.x.0.0 (where x can
be anything from 1 to 255). Answers D and F are incorrect because
access lists in the 200 range do not deal with TCP/IP, but Ethernet type
codes.
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10.
Answer D is correct. Traffic will be denied if the first 25 bits of the 32-bit
binary host address match 00001010.1100100.00101101.0xxxxxxx, as
0.0.0.127
in binary is equal to
00000000.0000000.00000000.01111111
The last 7 digits of the final octet are wild. 25 in binary is 00011001. You
can see from the decimal that the other first three octets already match,
and the first binary digit is the same as well—the list applies and the
traffic is denied.
Answer E is correct. Traffic will be denied if the first 25 bits of the 32-bit
binary host address match 00001010.1100100.00101101.0xxxxxxx, as
0.0.0.127
in binary is equal to
00000000.0000000.00000000.01111111
The last 7 digits of the final octet are wild. 118 in binary is 01110110.
You can see from the decimal that the other first three octets already
match, the first binary digit is the same as well—the list applies and the
traffic is denied.
Answers A and B are incorrect. Traffic from these hosts is not stopped
by the first line of access list 1 and is permitted by the second. Answer
C is incorrect. The first line of access list 1 does not stop traffic from this
host, only traffic from hosts on the 10.100.45.0 network with the last
quad's value less than 128 (a one must be the first number in the final
binary octet for it to not be a match). The second line of the access list
permits this traffic.
11.
Answer C is correct. Frame relay is relatively inexpensive; can provide
the option of bursting, which increases data transfer rate over the
agreed upon CIR; and allows new sites to be added to the network
quickly. Answer A is incorrect. Leased lines tend to be a lot more
expensive than packet-switched networks. It is also often a more
involved process to add new sites to such a WAN network than it is with
a technology like frame relay. Answer B is incorrect. Leased lines tend
to be a lot more expensive than packet-switched networks. It is also
often a more involved process to add new sites to such a WAN network
than it is with a technology like frame relay. Answer D is incorrect.
Although ATM, like frame relay, allows new sites to be added quickly, it
is generally more expensive than frame relay and is less likely to offer
extra bandwidth above the agreed upon amount.
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12.
Answer C is correct. HDLC is the default protocol used by Cisco
routers. Answer A is incorrect because SLIP is not the default protocol
used by Cisco routers. Answer B is incorrect. Although it is pervasive,
PPP is not the default protocol used by Cisco routers. Answer D is
incorrect. LAPB provides error recovery, but is not the default leasedline protocol used by Cisco routers.
13.
Answer A is correct. This is the sequence of IOS commands that you
would use to ensure that RIPv1, rather than RIPv1 and RIPv2, is being
used on the network. Answer B is incorrect. You do not use the
interface configuration mode to set up the specific RIP version that the
router should use. Answer C is incorrect because the version of RIP
must be specified after the router rip command has been entered, not
on the same line. Answer D is incorrect because the syntax in this
answer is incorrect.
14.
Answer C is correct. This answer correctly configures the EIGRP AS
(Autonomous System) number and the correct network (10.10.50.0).
Answer A is incorrect. This answer attempts to (incorrectly) configure
RIP rather than EIGRP. The network is also incorrect. Answer B is
incorrect. This answer configures the incorrect network. The network
stated in the question is 10.10.50.0, not 10.50.10.0. Answer D is
incorrect. This answer configures the wrong AS (Autonomous System)
number and the wrong network.
15.
Answers B, E, and F are correct because they specify the correct
subnet mask and the correct IP address for the interface. Answers A, C,
and D are incorrect because they specify an incorrect subnet mask for
the network interface.
16.
Answer A is correct. 10.10.10.31 is an addressable host if the subnet
mask 255.255.255.0 is used. Answer B is correct. 10.10.10.31 is an
addressable host if the subnet mask 255.255.255.192 is used. Answer
C is incorrect. 10.10.10.31 is a broadcast address if the subnet mask is
255.255.255.224. Answer D is incorrect. 10.10.10.31 is a broadcast
address if the subnet mask is 255.255.255.240. Answer E is incorrect.
10.10.10.31 is a broadcast address if the subnet mask is
255.255.255.248.
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17.
Answer B is correct. TACACS+ is used to support a router that runs as
a Terminal Server. Cisco recommends this protocol over RADIUS.
TACACS+ is proprietary to Cisco. Answer A is incorrect. Although
RADIUS can be used on a terminal server router to manage other
routers, Cisco recommends against this because it does not provide the
level of administrative granularity that TACACS+ does. Answers C and
D are incorrect. IGRP and OSPF are routing protocols, so they cannot
be directly used to manage other routers from a router that is configured
as a terminal server.
18.
Answer D is correct. The Cisco Catalyst 1900 switch supports 64
VLANs with a separate spanning tree. Answer A is incorrect. The Cisco
Catalyst 1900 switch supports 64 VLANs with a separate spanning tree.
Answer B is incorrect. The Cisco Catalyst 1900 switch supports 64
VLANs with a separate spanning tree. Answer C is incorrect. The Cisco
Catalyst 1900 switch supports 64 VLANs with a separate spanning tree.
Answer E is incorrect. The Cisco Catalyst 1900 switch supports 64
VLANs with a separate spanning tree.
19.
Answer C is correct. Show VLAN-membership will display a list of ports
and their corresponding VLAN-membership. Answer A is incorrect. The
IOS command to display the VLAN membership is show VLANmembership. List ports is not a valid IOS command. Answer B is
incorrect. The IOS command to display the VLAN membership is show
VLAN-membership. List VLAN is not a valid IOS command. Answer D is
incorrect. VLAN-membership is used to assign a port to a VLAN. It will
not display current port membership status.
20.
Answer D is correct. There are adequate ports in the administration
area, and all of the cabling on the factory floor is shielded. Answer A is
incorrect. The cable running from the administration area switch to the
factory floor switch is unshielded. STP should be used rather than UTP
because of the documented electromagnetic interference. Answer B is
incorrect. The cable running from the factory floor switch to the hosts on
the factory floor is unshielded. STP should be used rather than UTP
because of the documented electromagnetic interference. Answer C is
incorrect. The two switches that are allocated to the administration area
will not have enough ports to handle the 50 workstations and three
servers.
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21.
Answer A is correct because a bridge can segment a network in two,
thereby reducing the amount of unicast traffic on a segment. Answer B
is correct because a switch reduces the size of a segment to an
individual host. Answer C is incorrect. The school asked not to have the
network resubnetted, which would be necessary if a router was
implemented. Answer D is incorrect because repeater does not reduce
the size of a network segment.
22.
Answer B is correct. Store-and-forward switching copies the entire
frame into a buffer, performs a CRC (cyclic redundancy) check, and
then forwards error-free frames to their destination. Answer A is
incorrect. Fragment-free switching only examines the first 64 bytes of a
frame before forwarding it. Answer C is incorrect because cut-through
switching performs no error correction whatsoever on a frame. Answer
D is incorrect because basic switching is the same as cut through
switching. No error correction occurs using this method.
23.
Answer A is correct. Fragment free switching checks the first 64 bytes
of a frame for errors. If the frame is error free, it is forwarded to its
destination. Because only the first 64 bytes are checked, latency for this
method of switching does not increase with the size of the transmitted
frame. Answer B is incorrect. Store and forward switching checks the
entire frame. This means that latency increases as frame size
increases. The larger the frame, the longer it takes to check. Answers C
and D are incorrect because basic switching and cut through switching
provide no error correction.
24.
Answer D is correct. You do not have to enter the IP address of the
TFTP server until after this command is issued (it will prompt for one).
Answer A is incorrect because backup is not an IOS command. Answer
B is incorrect because backup is not an IOS command. Answer C is
incorrect; this will copy a startup-config file stored on the TFTP server to
the switch.
25.
Answer B is correct. This shorthand is commonly used to copy the
startup configuration to the running configuration of a router. Answer A
is incorrect. This will copy the running configuration to the startup
configuration. Answers C and D are incorrect because overwrite is not a
command in IOS.
26.
Answer A is correct. The hostname command is used to set the
hostname of a router. Answer B is incorrect. The set name command
does not exist within IOS. Answer C is incorrect. The configure name
command does not exist within IOS. Answer D is incorrect. The apply
name command does not exist within IOS.
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27.
Answer A is correct. Enable password CAPRICORNUS will set the
enable password to CAPRICORNUS. Line con 0 will put the router into
the mode where the console password can be set. Password AQUILA
will set the appropriate password. Answers B and D are incorrect
because enable password CAPRICORNUS will set the enable
password to CAPRICORNUS. Answer C is incorrect. Line vty 0 4 will
configure the VTY rather than CONSOLE password.
28.
Answer A is correct. CDP is enabled by default on Cisco Catalyst 1900
switches. Answer B is incorrect. By default, there is no console
password on a Cisco Catalyst 1900 switch. Answer C is incorrect. By
default, the Spanning Tree protocol is enabled on a Cisco Catalyst 1900
switch. Answer D is incorrect. By default, the switching mode is set to
FragmentFree. Answer E is incorrect. By default, the 10BaseT port is
set to half duplex.
29.
Answer E is correct. It assigns the correct IP, default gateway, and the
correct subnet mask to the switch. Answer A is incorrect because it
assigns the wrong subnet mask and default gateway to the switch.
Answer B is incorrect because it assigns the wrong default gateway to
the switch. Answer C is incorrect because it assigns the wrong IP
address, default gateway, and subnet mask to the switch. Answer D is
incorrect because it assigns the wrong subnet mask to the switch.
30.
Answer D is correct. The first goal is to stop traffic from a particular
internal network reaching the Internet. Traffic to the Internet from the
internal network travels inbound (into the router) across interface S1
and outbound (out of the router) across interface E0. Access list 4
applied inbound on s1 will meet the first goal, as it blocks the traffic from
the specified subnet. To meet the second goal, Access list 2 should be
applied to e0 inbound (that is, from the Internet to the router) to restrict
traffic from the Internet to that which is specified. Access list 2 could be
applied to s1 out and access list 4 to e0 out to achieve the same result;
however, this would require more work from the router. It was also not
presented as an option in this question. Answer A is incorrect. Traffic
from the Internet is inbound on interface e0 and outbound on interface
s1. These access lists also use the incorrect wildcard mask (Access list
1 permits traffic from x.x.x.0 where X is anywhere from 1 to 255).
Answer B is incorrect. These access lists use the incorrect wildcard
mask (Access list 1 permits traffic from x.x.x.0 where X is anywhere
from 1 to 255). Answer C is incorrect. Traffic from the Internet is
inbound on interface e0 and outbound on interface s1.
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31.
Answer B is correct. Although this access list should be applied to
incoming traffic on interface e0, applying it to outgoing traffic on
interface s1 will work as well. Answer A is incorrect because the
wildcard mask specifies the first three quads rather than the final quad
of 192.168.20.0. Answer C is incorrect. Applying this access list to
outgoing traffic on interface e0 will not work because all traffic from that
particular network originates on the network that is connected to the
interface and will therefore be incoming on e0. Answer D is incorrect
because the access list mask specifies the first three quads rather than
the final quad of 192.168.20.0. Answer E is incorrect; because answer
B will work, there is a correct answer.
32.
Answer D is correct. The interface is correctly chosen, the
encapsulation type is correct, and the keepalive setting is correctly set
at 20 seconds. Answer A is incorrect because the encapsulation is set
to ppp rather than frame-relay. Answer B is incorrect because the
interface is set to s1 instead of s0. Answer C is incorrect because the
encapsulation is set to ppp rather than frame-relay, and the keepalive is
set to 5 rather than 20.
33.
Answer B is correct, and answers A, C, and D are incorrect. Layer 1
deals with Bits. Layer 2 deals with Frames. Layer 3 deals with Packets.
Layer 4 deals with Segments.
34.
Answer C is correct. IP addresses are represented by Layer 3 of the
OSI model. Answers A, B, and D are incorrect, as they represent IP
addresses occurring at other layers of the OSI model.
35.
Answers C and D are correct. Repeaters and hubs do nothing to stop or
filter broadcast traffic; therefore, these devices could not be used to
reduce this type of congestion on the LAN. Answer A is incorrect. The
Catalyst 1900 switch can be configured with VLANs. VLANs do not
forward broadcast traffic; therefore, segmenting the network into several
VLANs might alleviate this problem. Answer B is incorrect. Routers do
not forward broadcast traffic. Segmenting the network with a router may
alleviate the broadcast traffic problem.
36.
Answer A is correct because it provides the correct syntax and is also
the only one that has the correct series of numbers. Answers B, C, and
D are incorrect because the syntax and number series are incorrect.
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37.
Answer D is correct. To answer this question you must work out what
the network address and broadcast address will be for each of the /29
networks that this /24 network has been divided into. You can only
assign an address that is neither a network nor a broadcast address to
a router interface. In answer D, this address is the first available host
address on network 192.168.10.152 /29. Answer A is incorrect.
192.168.10.15 is the broadcast address of network 192.168.10.8 /29.
Legitimate addresses would have been from .9 through to .14. Answer
B is incorrect. 102.168.10.223 is the broadcast address of network
192.168.10.116 /29. Legitimate addresses would have been from .117
through to .222. Answer C is incorrect. 192.168.10.184 is the network
address of network 192.168.10.184 /29. Legitimate addresses would
have been from .185 through to .190.
38.
Answers A and B are correct. To find which hosts are addressable and
which hosts are not, you must find what the networks are. To do this
divide the two /24 address spaces into a total of 16 equal-sized
networks. This comes to 8 equal sized networks per /24 address space.
As the networks are of equal size, the subnet mask of this new network
is straightforward to calculate. A /24 network is 1 network of 254 hosts.
A /24 network divided in two is 2 networks at /25 with 126 hosts. A /24
network divided in four is at /26 and has 62 hosts. A /24 network divided
in eight is at /27 and has 30 hosts per network division. So in this
question, taking two /24 networks and putting them into 16 equal-sized
networks results in 16 networks of 30 possible hosts. The final octet
network addresses of these networks will be .0, .32, .64, .96, .128, .160,
.192, and .224. If any of the answers have these numbers in the final
address, they cannot be assigned to hosts on the network. Similarly the
broadcast addresses of .31., .63, .95, .127, .159, .191, .223, and .255
cannot be addressed. Any answer that has these numbers in the final
octet cannot be assigned to a host. The question is looking for which
addresses cannot be assigned. Answer A (192.168.100.31) cannot be
assigned, as 192.168.100.31 is the broadcast address of network
192.168.100.0 /27. Therefore, answer A is a correct answer. Answer B
is a correct answer. 192.168.100.63 is the broadcast address of
network 192.168.100.32 /27. Answer C is incorrect because it is a host
address on the 192.168.101.192 /27 network. This address can be
assigned and hence is a wrong answer. Answer D is incorrect because
it is a host address on the 192.168.100.224 /27 network. This address
can be assigned and hence is a wrong answer. Answer E is incorrect
because it is a host address on the 192.168.100.128 /27 network. This
address can be assigned and hence is a wrong answer.
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39.
Answer B and Answer G are correct. See Figure 1 for a diagram.
Figure 1.
Answer B is correct. As host 192.168.10.165 is hosted off switch three,
this host would not be able to be pinged if switch three went down.
Answer G is correct. Although host 192.168.10.165 is hosted off switch
three and is unreachable, the break could have occurred on the
repeater or the switch. Answer A is incorrect. Host 192.168.10.80 can
ping host 192.168.10.200, thereby indicating that the router is
functional. Answer C is incorrect. Host 192.168.10.200 is contactable.
This means that switch four must be active. Answer D is incorrect.
Switch one lies between host 192.168.10.70 and host 192.168.10.200,
and these hosts can contact each other. Answer E is incorrect. Switch
two hosts 192.168.10.70, which is able to communicate across the
network. Answer F is incorrect. The repeater between switches one and
two lies between host 192.168.10.70 and host 192.168.10.200, and
these hosts can contact each other.
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40.
Answer B is correct. At no point do packets successfully traverse
interface s1 of the router. Use the diagram with the question to trace
each ping path. Of the options presented, this is the most likely from the
information you are given in the question. Answer A is incorrect.
Interface e0 is functional because packets can pass from host
10.10.10.14 to host 10.10.30.68. Answer C is incorrect. Interface s2 is
functional because packets can pass from host 10.10.10.14 to host
10.10.30.68. Answer D is incorrect. Host 10.10.20.58 can be pinged;
this would be impossible if the switch was down. Answer E is incorrect.
Switch Omega is functional because packets can pass from host
10.10.10.14 to host 10.10.30.68. Answer F is incorrect. Switch Beta is
functional because packets can pass from host 10.10.10.14 to host
10.10.30.68.
41.
Answer A is correct. All other traffic bar 10.10.100.0 /24 and
10.10.150.0 /24 should be allowed. This line is irrelevant to our
purpose. Answer D is correct. A router "reads" an access list from top to
bottom. Once traffic matches, the router stops "reading." Access list 1
matches all traffic from the network 10.10.0.0 /16, hence the traffic we
are interested in denying has already been permitted. Answers B and E
are incorrect. These lines do what we want them to, but they do not
have a chance to do so until line one is moved to the bottom of the list.
Answer C is incorrect. Line three is irrelevant to our purpose and should
be deleted.
42.
Answer D is correct. This change will allow HTTP access to all hosts on
the 192.168.0.0 /24 network; this was not specified in the goals. Answer
E is correct. This will allow, rather than deny as specified, telnet access
from target network to the destination network. Answer A is incorrect.
This modification must be made to meet the goal of allowing all hosts
access to the Web server on host 192.168.10.21. Answer B is incorrect.
This modification must be made to achieve the goal of blocking telnet
access to any host on the 192.168.10.0 /24 network from the
192.168.20.0 /24 network. Answer C is incorrect. This modification is
required, or else hosts on 192.168.44.0 /24 will not be able to FTP to
host 192.168.10.22.
43.
Answer C is correct, and answers A, B, and D are incorrect. Bits
represent Layer 1 communication. Frames represent Layer 2
communication. Packets represent Layer 3 communication. Segments
represent Layer 4 communication and Datagrams represent Layer 5
(and above) communication.
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44.
Answer A is correct because Bits represent Layer 1 communication.
Answer D is correct because Segments represent Layer 4
communication. Answer E is correct because Datagrams represent
Layer 5 (and above) communication. Answer B is incorrect. Frames
represent Layer 2 communication. Packets represent Layer 3
communication. Answer C is incorrect. Frames represent Layer 2
communication. Packets represent Layer 3 communication.
45.
Answers C and D are correct because spanning tree is designed to
ensure that there is only one path through the network. If multiple paths
exist, data can loop through the network indefinitely until it expires.
Answers A and B are incorrect because spanning tree is designed to
ensure that there is only one path through the network.
46.
Answer B is correct, and answers A, C, and D are incorrect. There will
be an STP root bridge for each broadcast domain. Two TCP/IP subnets
separated by a Cisco router equals two broadcast domains.
47.
Answer B is correct, and answers A, C, and D are incorrect. Unicast is
1:1. Multicast is 1:Many. Broadcast is 1:All.
48.
Answer B is correct. Switches do reduce the size of unicast collision
domains. Answer C is correct. Routers do reduce the size of broadcast
domains as they do not forward broadcast packets. Answer D is correct.
VLANs do not forward broadcast packets to other VLANs. Implementing
VLANs on a switch reduces the size of the broadcast domain. Answer A
is incorrect. Switches, without VLANs, forward broadcast packets on all
interfaces; therefore, they do not reduce the size of the broadcast
domain.
49.
Answer A is correct. RIPv2 uses distance vector logic to determine
routes. Answer C is correct. IGRP uses distance vector logic to
determine routes. Answer D is correct. EIGRP is a hybrid protocol that
makes use of both distance vector and link-state logic to determine
routes. Answer B is incorrect. OSPF uses link-state logic to determine
routes.
50.
Answer D is correct. BGP is an exterior routing protocol. Answer A is
incorrect. RIPv2 is an interior routing protocol. Answer B is incorrect.
IGRP is an interior routing protocol. Answer C is incorrect. OSPF is an
interior routing protocol.
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51.
Answer C is correct. TFTP is used for high-speed/low overhead file
transfer. It is commonly used on Cisco systems for backing up and
restoring config files and IOS images. Answer A is incorrect. HTTP is
generally not used for bidirectional file transfer. It also has greater
overhead than TFTP. Answer B is incorrect. Telnet is generally not
used for bidirectional file transfer. Answer D is incorrect. Although FTP
can be used to transfer files, TFTP is a better choice in this scenario
because FTP has a greater overhead than TFTP.
52.
Answer A is correct. A laptop running appropriate software can connect
via a special cable to the console port for direct router configuration.
Answer B is correct. A laptop running appropriate software can connect
via a special cable to the auxiliary port for direct router configuration.
Answer C is incorrect. A laptop cannot configure a router's initial setup
via the UTP port. Later, when the router is configured, a Telnet session
may be established via this port. Answer D is incorrect. A laptop cannot
configure a router's initial setup via the serial port.
53.
Answer C is correct. FLASH stores the IOS as well as additional
configuration files and alternate IOS images (depending on the size of
FLASH memory). Answer A is incorrect. RAM stores the running
configuration file, working memory, and routing tables. Answer B is
incorrect. The POST and Bootstrap are stored in ROM. Answer D is
incorrect. NVRAM stores the startup config file and the config register,
but does not store the IOS image.
54.
Answer A is correct. According to line one of the access list, FTP traffic
from 10.10.x.x to host 192.168.10.24 will be discarded. Answer B is
correct. Although none of the access lists specifically mention this
traffic, all access lists have an implicit deny statement at the end for any
traffic that does not match. Answer E is correct. According to line 2 of
the access list, these packets will be discarded. Answer C is incorrect.
According to line 3 of the access list, these packets will be allowed to
pass through. Answer D is incorrect. According to line 5 of the access
list, these packets will be allowed to pass through.
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55.
Answer D is correct. This is a difficult question that requires you to
understand access lists and their masks extremely well. The mask on
the second line of the access list:
ACCESS LIST 102 deny tcp 10.60.0.128 0.0.255.127 192.168.10.24 eq
ftp
stipulates that the first bit in the final octet is set but that other bits are
wild (127 = 011111111). The first bit is set by the access list at 1 (as it
is 128 in decimal, 10000000 in binary), meaning that this line of the list
will catch all values in the final decimal quad over and including 128. In
real life, you would not write an access list like this. The third quad is
wild. The final decimal quad is 200; therefore, the packet is discarded.
Answer A is incorrect. The fifth line of the access list will allow FTP
packets from this host to traverse the interface when this list is applied.
Once a packet matches a line in the access list, it stops being
processed. Answer B is incorrect. The fifth line of the access list will
allow FTP packets from this host to traverse the interface when this list
is applied. Once a packet matches a line in the access list, it stops
being processed. Answer C is incorrect. The mask on the second line of
the access list stipulates that the first bit in the final octet is set but that
other bits are wild (127 = 011111111). The first bit is set by the access
list at 1, meaning that this line of the list will catch all values in the final
decimal quad over and including 128. In real life, you would not write an
access list like this. The third quad is wild. The final decimal quad is 57;
therefore, the packet passes. If the final decimal quad had been over
128, like in answer D, then this packet would have been discarded.
Answer E is incorrect. The fifth line of the access list will allow ftp
packets from this host to traverse the interface when this list is applied.
Once a packet matches a line in the access list, it stops being
processed.
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Glossary
access list
Rules applied to a router that will determine traffic patterns for data.
administrative distance
A value that ranges from 0 through 255 that determines the priority of a source's
routing information.
advanced distance vector protocol
A routing protocol that combines the strengths of the distance vector and link
state routing protocols. Cisco's Enhanced Interior Gateway Routing Protocol
(EIGRP) is considered an advanced distance vector protocol.
Application layer
The highest layer of the OSI model (Layer 7). It is closest to the end user and
selects appropriate network services to support end-user applications such as
email and FTP.
area
See [autonomous system]
ARP (Address Resolution Protocol)
Used to map a known logical address to an unknown physical address. A device
performs an ARP broadcast to identify the physical address of a destination
device. This physical address is then stored in cache memory for later
transmissions.
Asynchronous Transfer Mode (ATM)
A dedicated-connection switching technology that organizes digital data into 53byte cell units and transmits them over a physical medium using digital signal
technology.
attenuation
A term that refers to the reduction in strength of a signal. Attenuation occurs with
any type of signal, whether digital or analog. Sometimes referred to as signal
loss.
autonomous system (AS)
A group of networks under common administration that share a routing strategy.
An autonomous system is sometimes referred to as a domain or area.
bandwidth
The available capacity of a network link over a physical medium.
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BGP (Border Gateway Protocol)
An exterior routing protocol that exchanges route information between
autonomous systems.
boot field
The lowest four binary digits of a configuration register. The value of the boot
field determines the order in which a router searches for Cisco IOS software.
BRI (Basic Rate Interface)
An ISDN interface that contains two B channels and one D channel for circuitswitched communication for data, voice, and video.
bridge
A device used to segment a LAN into multiple physical segments. A bridge uses
a forwarding table to determine which frames need to be forwarded to specific
segments. Bridges isolate local traffic to the originating physical segment but
forward all non-local and broadcast traffic.
Bridge Protocol Data Unit (BDPU)
Data messages that are exchanged across the switches within an extended LAN
that uses a spanning tree protocol topology.
broadcast
A data frame that every node on a local segment will be sent.
buffering
A method of flow control used by the Transport layer that involves the memory
buffers on the receiving hosts. The Transport layer of the receiving system
ensures that sufficient buffers are available and that data is not transmitted at a
rate that exceeds the rate at which the receiving system can process it.
carrier detect signal
A signal received on a router interface that indicates whether the Physical layer
connectivity is operating properly.
CDP (Cisco Discovery Protocol)
A Cisco proprietary protocol that operates at the Data Link layer. CDP enables
network administrators to view a summary protocol and address information
about other directly connected Cisco routers (and some Cisco switches).
channel
A single communications path on a system. In some situations, channels can be
multiplexed over a single connection.
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CHAP (Challenge Handshake Authentication Protocol)
An authentication protocol for the Point-to-Point Protocol (PPP) that uses a threeway, encrypted handshake to force a remote host to identify itself to a local host.
checksum
A field that performs calculations to ensure the integrity of data.
CIDR (Classless Interdomain Routing)
Implemented to resolve the rapid depletion of IP address space on the Internet
and to minimize the number of routes on the Internet. CIDR provides a more
efficient method of allocating IP address space by removing the concept of
classes in IP addressing. CIDR enables routes to be summarized on powers-oftwo boundaries, thus reducing multiple routes into a single prefix.
CIR (Committed Information Rate)
The rate at which a Frame Relay link transmits data, averaged over time. CIR is
measured in bits per second.
classful addressing
Categorizes IP addresses into ranges that are used to create a hierarchy in the
IP addressing scheme. The most common classes are A, B, and C, which can be
identified by looking at the first three binary digits of an IP address.
classless addressing
Also commonly known as supernetting. The limited number of IP addresses was
causing major concern and there was a huge waste of addressing as well, as
routing became an issue. Because of a new hierarchical distribution of
addresses, classless addressing resolved many concerns.
CO (central office)
The local telephone company office where all local loops in an area connect.
configuration register
A numeric value (typically displayed in hexadecimal form) used to specify certain
actions on a router.
congestion
A situation that occurs during data transfer if one or more computers generate
network traffic faster than it can be transmitted through the network.
connectionless network services
Connectionless network services involve using a permanently established link.
Path selection and bandwidth allocation are done dynamically.
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connection-oriented network services
Connection-oriented network services involve using a nonpermanent path for
data transfer between systems. In order for two systems to communicate, they
must establish a path that will be used for the duration of their connection.
console
A terminal attached directly to the router for configuring and monitoring the
router.
convergence
The process by which all routers within an internetwork route information and
eventually agree on optimal routes through the internetwork.
counting to infinity
A routing problem in which the distance metric for a destination network is
continually increased because the internetwork has not fully converged.
CPE (customer premise equipment)
Terminating equipment such as telephones and modems supplied by the service
provider, installed at the customer site, and connected to the network.
CRC (cyclic redundancy check)
An error-checking mechanism by which the receiving node calculates a value
based on the data it receives and compares it with the value stored within the
frame from the sending node.
CSMA/CD (Carrier Sense Multiple Access/Collision Detection)
A physical specification used by Ethernet to provide contention-based frame
transmission. CSMA/ CD specifies that a sending device must share physical
transmission media and listen to determine whether a collision occurs after
transmitting. In simple terms, this means that an Ethernet card has a built-in
capability to detect a potential packet collision on the internetwork.
cut-through switching
A method of forwarding frames based on the first 6 bytes contained in the frame.
Cut-through switching provides higher throughput than store-and-forward
switching because it requires only 6 bytes of data to make the forwarding
decision. Cut-through switching does not provide error checking like its
counterpart store-and-forward switching.
DARPA (Defense Advanced Research Projects Agency)
A government agency that develops advanced defense capabilities. It is now
known as ARPA.
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DCE (data communications equipment)
The device at the network end of a user-to-network connection that provides a
physical connection to the network, forwards traffic, and provides a clocking
signal used to synchronize data transmission between the DCE and DTE
devices.
DDR (dial-on-demand routing)
The technique by which a router can initiate and terminate a circuit-switched
connection over ISDN or telephone lines to meet network traffic demands.
de-encapsulation
The process by which a destination peer layer removes and reads the control
information sent by the source peer layer in another network host.
default mask
A binary or decimal representation of the number of bits used to identify an IP
network. The class of the IP address defines the default mask. A default mask is
represented by four octets of binary digits. The mask can also be presented in
dotted decimal notation.
default route
A network route (that usually points to another router) established to receive and
attempt to process all packets for which no route appears in the route table.
delay
The amount of time necessary to move a packet through the internetwork from
source to destination.
demarc
The point of demarcation is between the carrier's equipment and the customer
premise equipment (CPE).
discard eligibility bit
A bit that can be set to indicate that a frame may be dropped if congestion occurs
within the Frame Relay network.
distance vector protocol
An interior routing protocol that relies on distance and vector or direction to
choose optimal paths. distance vector protocol requires each router to send all or
a large part of its route table to its neighboring routers periodically.
DLCI (data link connection identifier)
A value that specifies a permanent virtual circuit (PVC) or switched virtual circuit
(SVC) in a Frame Relay network.
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DNS (Domain Name System)
A system used to translate fully qualified hostnames or computer names into IP
addresses, and vice versa.
domain
See [autonomous system]
dotted decimal notation
A method of representing binary IP addresses in a decimal format. Dotted
decimal notation represents the four octets of an IP address in four decimal
values separated by decimal points.
DTE (data terminal equipment)
The device at the user end of the user-to-network connection that connects to a
data network through a data communications equipment (DCE) device.
dynamic route
A network route that adjusts automatically to changes within the internetwork.
EGP (Exterior Gateway Protocol)
An exterior routing protocol that exchanges route information between
autonomous systems. EGP has become obsolete and is being replaced by the
Border Gateway Protocol (BGP).
EIGRP (Enhanced Interior Gateway Routing Protocol)
A Cisco proprietary routing protocol that includes features of both distance vector
and link state routing protocols. EIGRP is considered an advanced distance
vector protocol.
encapsulation
Generally speaking, encapsulation is the process of wrapping data in a particular
protocol header. In the context of the OSI model, encapsulation is the process by
which a source peer layer includes header and/or trailer control information with
a Protocol Data Unit (PDU) destined for its peer layer in another network host.
The information encapsulated instructs the destination peer layer how to process
the information.
EXEC
The user interface for executing Cisco router commands.
exterior routing protocol
A routing protocol that conveys information between autonomous systems; it is
widely used within the Internet. The Border Gateway Protocol (BGP) is an
example of an exterior routing protocol.
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FCS (frame check sequence)
Extra characters added to a frame for error control purposes. FCS is the result of
a cyclic redundancy check (CRC).
Flash
Router memory that stores the Cisco IOS image and associated microcode.
Flash is erasable, reprogrammable ROM that retains its content when the router
is powered down or restarted.
flat routing protocol
A routing environment in which all routers are considered peers and can
communicate with any other router in the network as directly as possible. A flat
routing protocol functions well in simple and predictable network environments.
flow control
A mechanism that throttles back data transmission to ensure that a sending
system does not overwhelm the receiving system with data.
Forward Explicit Congestion Notification (FECN)
A Frame Relay message that notifies the receiving device that there is
congestion in the network. An FECN bit is sent in the same direction in which the
frame was traveling, toward its destination.
Frame Relay
A switched Data Link layer protocol that supports multiple virtual circuits using
High-level Data Link Control (HDLC) encapsulation between connected devices.
frame tagging
A method of tagging a frame with a unique user-defined virtual local area network
(VLAN). The process of tagging frames allows VLANs to span multiple switches.
FTP (File Transfer Protocol)
A protocol used to copy a file from one host to another host, regardless of the
physical hardware or operating system of each device. FTP identifies a client and
server during the file-transfer process. In addition, it provides a guaranteed
transfer by using the services of the Transmission Control Protocol (TCP).
full-duplex
The physical transmission process on a network device by which one pair of
wires transmits data while another pair of wires receives data. Full-duplex
transmission is achieved by eliminating the possibility of collisions on an Ethernet
segment, thereby eliminating the need for a device to sense collisions.
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function
A term that refers to the different devices and the hardware tasks these devices
perform within ISDN.
global configuration mode
A router mode that enables simple router configuration commands, such as
router names, banners, and passwords, to be executed. Global configuration
commands affect the whole router rather than a single interface or component.
GNS (Get Nearest Server)
A request sent by an Internetwork Packet Exchange (IPX) client to locate the
closest active server of a particular service. Depending on where the service can
be located, either a server or a router can respond to the request.
half-duplex
The physical transmission process whereby one pair of wires is used to transmit
information and the other pair of wires is used to receive information or to sense
collisions on the physical media. Half-duplex transmission is required on Ethernet
segments with multiple devices.
handshake
The process of one system making a request to another system prior to a
connection being established. Handshakes occur during the establishment of a
connection between two systems, and they address matters such as
synchronization and connection parameters.
HDLC (High-level Data Link Control)
A bit-oriented, synchronous Data Link layer protocol that specifies data
encapsulation methods on serial links.
Header
Control information placed before the data during the encapsulation process.
hierarchical routing protocol
A routing environment that relies on several routers to compose a backbone.
Most traffic from non-backbone routers traverses the backbone routers (or at
least travels to the backbone) to reach another non-backbone router. This is
accomplished by breaking a network into a hierarchy of networks, where each
level is responsible for its own routing.
hold-down
The state into which a route is placed so that routers will not advertise or accept
updates for that route until a timer expires.
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hop count
The number of routers a packet passes through on its way to the destination
network.
hostname
A logical name given to a router.
HSSI (High-Speed Serial Interface)
A physical standard designed for serial connections that require high data
transmission rates. The HSSI standard allows for high-speed communication that
runs at speeds up to 52Mbps.
ICMP (Internet Control Message Protocol)
A protocol that communicates error messages and controls messages between
devices. Thirteen different types of ICMP messages are defined. ICMP allows
devices to check the status of other devices, to query the current time, and to
perform other functions such as ping and traceroute.
IEEE (Institute of Electrical and Electronics Engineers)
An organization that defines standards for network LANs, among other things.
The IEEE is the industry standard used in today's computing world.
IGRP (Interior Gateway Routing Protocol)
A Cisco proprietary distance vector routing protocol that uses hop count as its
metric.
initial configuration dialog
The dialog used to configure a router the first time it is booted or when no
configuration file exists. The initial configuration dialog is an optional tool used to
simplify the configuration process.
integrated routing
A technique in which a router that is routing multiple routed protocols shares
resources. Rather than using several routing protocols to support multiple routed
protocols, a network administrator can use a single routing protocol to support
multiple routed protocols. The Enhanced Interior Gateway Routing Protocol
(EIGRP) is an example of a routing protocol that supports integrated routing.
interdomain router
A router that uses an exterior routing protocol, such as the Border Gateway
Protocol (BGP), to exchange route information between autonomous systems.
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interfaces
Router components that provide the network connections where data packets
move in and out of the router. Depending on the model of router, interfaces exist
either on the motherboard or on separate, modular interface cards.
interior routing protocol
A routing protocol that exchanges information within an autonomous system.
Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP),
and Open Shortest Path First (OSPF) are examples of interior routing protocols.
intradomain router
A router that uses an interior routing protocol, such as the Interior Gateway
Routing Protocol (IGRP), to convey route information within an autonomous
system.
IP (Internet Protocol)
One of the many protocols maintained in the TCP/IP suite of protocols. IP is the
transport mechanism for Transmission Control Protocol (TCP), User Datagram
Protocol (UDP), and Internet Control Message Protocol (ICMP) data. It also
provides the logical addressing necessary for complex routing activity.
IP extended access list
An access list that provides a way of filtering IP traffic on a router interface based
on the source and destination IP address or port, IP precedence field, TOS field,
ICMP-type, ICMP-code, ICMP-message, IGMP-type, and TCP-established
connections.
IP standard access list
An access list that provides a way of filtering IP traffic on a router interface based
on the source IP address or address range.
IPX (Internetwork Packet Exchange)
The Layer 3 protocol used within NetWare to transmit data between servers and
workstations.
IPX extended access list
An access list that provides a way of filtering IPX traffic on a router interface
based on the source and destination IPX address or address range, IPX protocol,
and source and destination sockets.
IPX SAP filter
A method of filtering SAP traffic on a router interface. SAP filters are used to filter
SAP traffic origination or traffic destined for specific IPX addresses or address
ranges.
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IPX standard access list
An access list that provides a way of filtering IPX traffic on a router interface
based on the source IPX address or address range.
ISDN (Integrated Services Digital Network)
A communications protocol offered by telephone companies that permits
telephone networks to carry data, voice, and other traffic.
ISL (interswitch link)
A protocol used to allow virtual local area networks (VLANs) to span multiple
switches. ISL is used between switches to communicate common VLANs
between devices.
keepalive frames
Protocol Data Units (PDUs) transmitted at the Data Link layer that indicate
whether the proper frame type is configured.
LAN protocols
Protocols that identify Layer 2 protocols used for the transmission of data within a
local area network (LAN). The three most popular LAN protocols used today are
Ethernet, token ring, and Fiber Distributed Data Interface (FDDI).
LCP (Link Control Protocol)
A protocol that configures, tests, maintains, and terminates Point-to-Point
Protocol (PPP) connections.
link state packet
A broadcast packet that contains the status of a router's links or network
interfaces.
link state protocol
An interior routing protocol in which each router sends only the state of its own
network links across the network, but sends this information to every router within
its autonomous system or area. This process enables routers to learn and
maintain full knowledge of the network's exact topology and how it is
interconnected. Link state protocols use a "shortest path first" algorithm.
LLC (Logical Link Control) sublayer
A sublayer of the Data Link layer. The LLC sublayer provides the software
functions of the Data Link layer.
LMI (Local Management Interface)
A set of enhancements to the Frame Relay protocol specifications used to
manage complex networks. Some key Frame Relay LMI extensions include
global addressing, virtual circuit status messages, and multicasting.
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load
An indication of how busy a network resource is. CPU utilization and packets
processed per second are two indicators of load.
local loop
The line from the customer's premises to the telephone company's central office
(CO).
logical addressing
Network layer addressing is most commonly referred to as logical addressing
(versus the physical addressing of the Data Link layer). A logical address
consists of two parts: the network and the node. Routers use the network part of
the logical address to determine the best path to the network of a remote device.
The node part of the logical address is used to identify the specific node to
forward the packet on the destination network.
logical ANDing
A process of comparing two sets of binary numbers to result in one value
representing an IP address network. Logical ANDing is used to compare an IP
address against its subnet mask to yield the IP subnet on which the IP address
resides. ANDing is also used to determine whether a packet has a local or
remote destination.
MAC address
A physical address used to define a device uniquely.
MAC (Media Access Control) layer
A sublayer of the Data Link layer that provides the hardware functions of the
Data Link layer.
metric
The relative cost of sending packets to a destination network over a specific
network route. Examples of metrics include bandwidth, delay, and reliability.
MIB (management information database)
A database that maintains statistics on certain data items. The Simple Network
Management Protocol (SNMP) uses MIBs to query information about devices.
multicasting
A process of using one IP address to represent a group of IP addresses.
Multicasting is used to send messages to a subset of IP addresses in a network
or networks.
multipath routing protocol
A routing protocol that load-balances over multiple optimal paths to a destination
network when the costs of the paths are equal.
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multiplexing
A method of flow control used by the Transport layer in which application
conversations are combined over a single channel by interleaving packets from
different segments and trans mitting them.
NBMA (nonbroadcast multiaccess)
A multiaccess network that either does not support broadcasts or for which
sending broadcasts is not feasible.
NCP (NetWare Core Protocol)
A collection of upper-layer server routines that satisfy requests from other
applications.
NCP (network control protocol)
A collection of protocols that establishes and configures different Network layer
protocols for use over a Point-to-Point Protocol (PPP) connection.
NetBIOS (Network Basic Input/Output System)
A common Session layer interface specification from IBM and Microsoft that
enables applications to request lower-level network services.
NetWare
A popular LAN operating system developed by Novell Corporation that runs on a
variety of different types of LANs.
NetWare shell
An upper-layer NetWare service that determines whether application calls require
additional network services.
network discovery
When a router starts up, this is the process by which it learns of its internetwork
environment and begins to communicate with other routers.
NIC (network interface card)
A board that provides network communication capabilities to and from a network
host.
NLSP (NetWare Link State Protocol)
A link state routing protocol used for routing Internetwork Package Exchange
(IPX).
NOS (network operating system)
A term used to describe distributed file systems that support file sharing, printing,
database access, and other similar applications.
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NVRAM (nonvolatile random access memory)
A memory area of the router that stores permanent information, such as the
router's backup configuration file. The contents of NVRAM are retained when the
router is powered down or restarted.
OSI (Open Systems Interconnection) model
A layered networking framework developed by the International Organization for
Standardization. The OSI model describes seven layers that correspond to
specific networking functions.
OSPF (Open Shortest Path First)
A hierarchical link state routing protocol that was developed as a successor to
the Routing Information Protocol (RIP).
packet switching
A process by which a router moves a packet from one interface to another.
PAP (Password Authentication Protocol)
An authentication protocol for the Point-to-Point Protocol (PPP) that uses a twoway, unencrypted handshake to enable a remote host to identify itself to a local
host.
parallelization
A method of flow control used by the Transport layer in which multiple channels
are combined to increase the effective bandwidth for the upper layers;
synonymous with multilink.
path length
The sum of the costs of each link traversed up to the destination network. Some
routing protocols refer to path length as hop count.
PDU (Protocol Data Unit)
A unit of measure that refers to data that is transmitted between two peer layers
within different network devices. Segments, packets, and frames are examples of
PDUs.
peer-to-peer communication
A form of communication that occurs between the same layers of two different
network hosts.
physical connection
A direct connection between two devices.
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ping
A tool for testing IP connectivity between two devices. Ping is used to send
multiple IP packets between a sending and a receiving device. The destination
device responds with an Internet Control Message Protocol (ICMP) packet to
notify the source device of its existence.
POP (point of presence)
A physical location where a carrier has installed equipment to interconnect with a
local exchange carrier.
PPP (Point-to-Point Protocol)
A standard protocol that enables router-to-router and host-to-network
connectivity over synchronous and asynchronous circuits such as telephone
lines.
Presentation layer
Layer 6 of the OSI model. The Presentation layer is concerned with how data is
represented to the Application layer.
PRI (Primary Rate Interface)
An ISDN interface that contains 23 B channels and 1 D channel for circuitswitched communication for data, voice, and video. In North America and Japan,
a PRI contains 23 B channels and 1 D channel. In Europe, it contains 30 B
channels and 1 D channel.
privileged mode
An extensive administrative and management mode on a Cisco router. This
router mode permits testing, debugging, and commands to modify the router's
configuration.
protocol
A formal description of a set of rules and conventions that defines how devices
on a network must exchange information.
PSTN (public switched telephone network)
The circuit-switching facilities maintained for voice analog communication.
PVC (permanent virtual circuit)
A virtual circuit that is permanently established and ready for use.
RAM (random access memory)
A memory area of a router that serves as a working storage area. RAM contains
data such as route tables, various types of caches and buffers, as well as input
and output queues and the router's active configuration file. The contents of RAM
are lost when the router is powered down or restarted.
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RARP (Reverse Address Resolution Protocol)
This protocol provides mapping that is exactly opposite to the Address
Resolution Protocol (ARP). RARP maps a known physical address to a logical
address. Diskless machines that do not have a configured IP address when
started typically use RARP. RARP requires the existence of a server that
maintains physical-to-logical address mappings.
reference point
An identifier of the logical interfaces between functions within ISDN.
reliability
A metric that allows the network administrator to assign arbitrarily a numeric
value to indicate a reliability factor for a link. The reliability metric is a method
used to capture an administrator's experience with a given network link.
RIP (Routing Information Protocol)
A widely used distance vector routing protocol that uses hop count as its metric.
ROM (read-only memory)
An area of router memory that contains a version of the Cisco IOS image—
usually an older version with minimal functionality. ROM also stores the bootstrap
program and power-on diagnostic programs.
ROM monitor
A mode on a Cisco router in which the executing software is maintained in ROM.
ROM monitor mode (RXBOOT)
A router-maintenance mode that enables router recovery functions when the IOS
file in Flash has been erased or is corrupt.
route aggregation
The process of combining multiple IP address networks into one superset of IP
address networks. Route aggregation is implemented to reduce the number of
route table entries required to forward IP packets accurately in an internetwork.
route poisoning
A routing technique by which a router immediately marks a network as
unreachable as soon as it detects that the network is down. The router
broadcasts the update throughout the network and maintains this poisoned route
in its route table for a specified period of time.
route table
An area of a router's memory that stores the network topology information used
to determine optimal routes. Route tables contain information such as destination
network, next hop, and associated metrics.
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routed protocol
A protocol that provides the information required for the routing protocol to
determine the topology of the internetwork and the best path to a destination.
The routed protocol provides this information in the form of a logical address and
other fields within a packet. The information contained in the packet allows the
router to direct user traffic. The most common routed protocols include Internet
Protocol (IP) and Internetwork Packet Exchange (IPX).
router modes
Modes that enable the execution of specific router commands and functions.
User, privileged, and setup are examples of router modes that allow you to
perform certain tasks.
routing algorithms
Well-defined rules that aid routers in the collection of route information and the
determination of the optimal path.
routing loop
An event in which two or more routers have not yet converged and are
propagating their inaccurate route tables. In addition, they are probably still
switching packets based on their inaccurate route tables.
routing protocols
Routing protocols use algorithms to generate a list of paths to a particular
destination and the cost associated with each path. Routers use routing protocols
to communicate among each other the best route to use to reach a particular
destination.
RS-232
A physical standard used to identify cabling types for serial data transmission for
speeds of 19.2Kbps or less. RS-232 connects two devices communicating over a
serial link with either a 25-pin (DB-25) or 9-pin (DB-9) serial interface. RS-232 is
now known as EIA/TIA-232.
running configuration file
The executing configuration file on a router.
SAP (Service Advertisement Protocol)
An Internetwork Package Exchange (IPX) protocol that serves as a means to
inform network clients of available network resources and services.
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SDLC (Synchronous Data Link Control)
Primarily used for terminal-to-mainframe communication, SDLC requires that one
device be labeled as the primary station and all other devices be labeled as
secondary stations. Communication can only occur between the primary station
and a secondary station.
session
A dialogue between two or more different systems.
Session layer
As Layer 5 of the OSI model, the Session layer is concerned with establishing,
managing, and terminating sessions between applications on different network
devices.
setup mode
The router mode triggered on startup if no configuration file resides in nonvolatile
random access memory (NVRAM).
shortest path first
See [link state protocol]
single-path routing protocol
A routing protocol that uses only one optimal path to a destination.
sliding windows
A method by which TCP dynamically sets the window size during a connection,
allowing either device involved in the communication to slow down the sending
data rate based on the other device's capacity.
SMTP (Simple Mail Transfer Protocol)
A protocol used to pass mail messages between devices, SMTP uses
Transmission Control Protocol (TCP) connections to pass the email between
hosts.
socket
The combination of the sending and destination Transmission Control Protocol
(TCP) port numbers and the sending and destination Internet Protocol (IP)
addresses defines a socket. Therefore, a socket can be used to define any User
Datagram Protocol (UDP) or TCP connection uniquely.
Spanning Tree Protocol
A protocol used to eliminate all circular routes in a bridged or switched
environment while maintaining redundancy. Circular routes are not desirable in
Layer 2 networks because of the forwarding mechanism employed at this layer.
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split horizon
A routing mechanism that prevents a router from sending information that it
received about a network back to its neighbor that originally sent the information.
This mechanism is very useful in preventing routing loops.
SPX (Sequenced Packet Exchange)
The Layer 4 protocol used within NetWare to ensure reliable, connection-oriented
services.
startup configuration file
The backup configuration file on a router.
static route
A network route that is manually entered into the route table. Static routes
function well in very simple and predictable network environments.
store-and-forward switching
A method of forwarding frames by copying an entire frame into the buffer of a
switch and making a forwarding decision. Store-and-forward switching does not
achieve the same throughput as its counterpart, cut-through switching, because it
copies the entire frame into the buffer instead of copying only the first 6 bytes.
Store-and-forward switching, however, provides error checking that is not
provided by cut-through switching.
subinterface
One of possibly many virtual interfaces on a single physical interface.
subnetting
A process of splitting a classful range of IP addresses into multiple IP networks to
allow more flexibility in IP addressing schemes. Subnetting overcomes the
limitation of address classes and allows network administrators the flexibility to
assign multiple networks with one class of IP addresses.
switch
A switch provides increased port density and forwarding capabilities as
compared to bridges. The increased port densities of switches allow LANs to be
microsegmented, thereby increasing the amount of bandwidth delivered to each
device.
TCP (Transmission Control Protocol)
One of the many protocols maintained in the TCP/IP suite of protocols. TCP
provides a connection-oriented and reliable service to the applications that use it.
TCP three-way handshake
A process by which TCP connections send acknowledgments between each
other when setting up a TCP connection.
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TCP windowing
A method of increasing or reducing the number of acknowledgments required
between data transmissions. This allows devices to throttle the rate at which data
is transmitted.
Telnet
A standard protocol that provides a virtual terminal. Telnet enables a network
administrator to connect to a router remotely.
TFTP (Trivial File Transfer Protocol)
A protocol used to copy files from one device to another. TFTP is a strippeddown version of FTP.
tick
A measure of network delay time about 1/18th of a second. In RIP version 2,
ticks serve as the primary value used to determine the best path.
traceroute
An IP service that allows a user to utilize the services of the User Datagram
Protocol (UDP) and the Internet Control Message Protocol (ICMP) to identify the
number of hops between sending and receiving devices and the paths taken
from the sending to the receiving device. Traceroute also provides the IP address
and DNS name of each hop. Typically, traceroute is used to troubleshoot IP
connectivity between two devices.
trailer
Control information placed after the data during the encapsulation process.
See also [encapsulation]
Transport layer
As Layer 4 of the OSI model, it is concerned with segmenting upper-layer
applications, establishing end-to-end connectivity through the network, sending
segments from one host to another, and ensuring the reliable transport of data.
trunk
A switch port that connects to another switch to allow virtual local area networks
(VLANs) to span multiple switches.
tunnel
A tunnel takes packets or frames from one protocol and places them inside
frames from another network system.
See also [encapsulation]
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UDP (User Datagram Protocol)
One of the many protocols maintained in the TCP/IP suite of protocols, UDP is a
Layer 4, best-effort delivery protocol and, therefore, maintains connectionless
network services.
user mode
A display-only mode on a Cisco router. Only limited information about the router
can be viewed within this router mode; no configuration changes are permitted.
V.35
A physical standard used to identify cabling types for serial data transmission for
speeds up to 4Mbps. The V.35 standard was created by the International
Telecommunication Union-Telecommunication (ITU-T) standardization sector.
virtual connection
A logical connection between two devices created through the use of
acknowledgments.
VLAN (virtual local area network)
A technique of assigning devices to specific LANs based on the port to which
they attach on a switch rather than the physical location. VLANs extend the
flexibility of LANs by allowing devices to be assigned to specific LANs on a portby-port basis versus a device basis.
VLSM (variable-length subnet masking)
VLSM provides more flexibility in assigning IP address space. (A common
problem with routing protocols is the necessity of all devices in a given routing
protocol domain to use the same subnet mask.) Routing protocols that support
VLSM allow administrators to assign IP networks with different subnet masks.
This increased flexibility saves IP address space because administrators can
assign IP networks based on the number of hosts on each network.
VTP
With VTP, an administrator can make configuration changes centrally on a single
Catalyst series switch and have those changes automatically communicated to
all the other switches in the network.
WANs (wide area networks)
WANs use data communications equipment (DCE) to connect multiple LANs.
Examples of WAN protocols include but are not limited to Frame Relay, Point-toPoint Protocol (PPP), High-level Data Link Control (HDLC), and Integrated
Services Digital Network (ISDN).
well-known ports
A set of ports between 1 and 1,023 that are reserved for specific TCP/IP
protocols and services.
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CONCLUSION.
THANK YOU.
I hope you have enjoyed your journey with this course CCNA (Cisco Certified
Network Associate) (640-801). May this be a significant step in your journey of
success?
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CCNA (Cisco Certified Network
Associate) (640-801).
© Copyright by CTF Services Limited 2005
All rights reserved worldwide. No part of this book may be reproduced or transmitted in
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