For Dummies CCENT Certification All-In-One

For Dummies CCENT Certification All-In-One
Chapter 1: Network Security
In This Chapter
✓ Introduction to security terminology
✓ Identifying types of attacks
✓ Looking at security devices
✓ Mitigating security threats
ne of the most important skills to have if you are going to support networked systems or systems connected to the Internet is the ability of
securing systems and networks. In order to be successful as a network professional today, you need to have a solid understanding of network security
and ways to protect the network.
I remember when a close friend of mine had his Web site totally replaced
by a hacker. My friend’s Web site files were replaced with inappropriate
content, and he wondered how on Earth someone had hacked his server. It
seems amazing now, but back then (circa 1994) a lot of companies did not
use firewalls because they were not aware of the risks involved in having a
computer connected directly to the Internet. Back then, people thought, “I
have a password on the administrator account, so I am secure.”
In this chapter, you find out about the basic concepts and terminology
related to information system security and network security. Be sure to read
this chapter carefully, and make sure you understand the topics, as you will
be tested on basic security concepts with the CCENT certification exam.
Have fun with this topic area — security is a very exciting field!
Quick Assessment
Quick Assessment
(True/False). A packet-filtering firewall checks the state of the
A ______ is responsible for creating a secure tunnel over an unsecure
The term used for controlling who is allowed to access a resource is
(True/False). A dictionary attack calculates all potential passwords.
A ______ virus is a self-replicating virus.
False. See “Firewalls.”
VPN. Review “Virtual Private Networks.”
Authorization. Check out “Authorization.”
False. Peruse “Password attacks.”
Worm. Take a look at “Worm.”
Introduction to Security Terminology
Introduction to Security Terminology
Let me start the discussion by going over some basic security concepts and
terminology. The CCENT certification exam expects you to have some
background in security best practices, so this chapter is designed to expose
the concepts to you. The next chapter looks at specific steps you need to
take to secure your Cisco devices.
Authentication is the process of proving one’s identity to the network
environment. Typically, authentication involves typing a username and
password on a system, and it is then verified against an account database
before you are granted access. There are different methods you can use to
authenticate to a system or network — you can supply a valid username and
password or maybe even use biometrics to be authenticated. Biometrics is
the concept of using a unique physical characteristic of yourself to authenticate
to the system, such as a fingerprint, a retina scan, or voice recognition to
prove your identity.
Consider these three different forms of authentication, known as authentication
factors, and their uses:
✦ Something you have: Dependent on the user having an object in her
possession to prove who she is. An example of this authentication is
possession of an ID card or door key.
✦ Something you know: Dependent on the user knowing a piece of
information to validate who he is. Examples of this are knowledge of a
password, pass code, or even a PIN (personal identification number).
✦ Something you are: Dependent on you proving your identity by
something you are, such as a fingerprint or retina scan — so biometrics
falls into this authentication factor.
Most authentication systems use a two-form authentication factor, where
two of the three factors mentioned here are used. For example, it is not
enough to have the ATM card in your possession to use it — you must know
the PIN for that card as well.
Smart card
A popular authentication device used today in networking environments
is a smart card, which is a small, ATM card–like device that contains your
account information. You insert the smart card into a smart card reader
that is connected to a computer, and then you enter the PIN associated with
the smart card. This is an example of securing an environment by requiring
the user to not only have the card, but also know the PIN — an example of
two-form authentication.
Introduction to Security Terminology
Using strong passwords
A number of years ago, I had a coworker
who was always trying to get me to guess his
passwords. He thought I had some magical
trick or program that was cracking them, but
all I was doing was guessing his passwords. I
remember one time he changed it, and I could
not guess it — until one night when we were
at a social function for work and all he talked
about was the Flyers hockey team. I remember
sitting there thinking, “I bet that is his
password.” Sure enough, the next day at work,
I tried flyers as his password, and it worked.
Now the lesson here is that he should have
at least mixed the case of the word flyers to
make something like flYeRs, or even better,
thrown a symbol in there by replacing the s
with a $. I would have had a much harder time
trying to guess his password if he had used
flYeR$ instead. This is an example of a strong
Strong passwords
It is really hard to talk about authentication without talking about ensuring
your usage of strong passwords on systems and devices. A strong password
is a password that is very difficult for hackers to guess or crack because it
contains a mix of uppercase and lowercase characters, a mix of numbers
and letters, and is a minimum of six characters long.
After someone is authenticated to a system or device, he is then granted or
denied access to resources such as files and printers, or given limited
privileges to a device. Authorization is the process of giving a person
permission to access a resource or a device.
Do not confuse authentication and authorization: You must be first
authenticated to the network; then, after authentication, you can access the
resources and perform the tasks that you have been authorized for.
Vulnerability is the term we use for a weakness in a system or device. The
vulnerability is created accidentally by the manufacturer and is typically the
result of a code mistake in the software or firmware.
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An example of authorization in the networking world is choosing to
authorize a system on the network (meaning we allow it to connect to the
network through a port on the switch) by its MAC address. In high-security
environments, this is very popular, and in the Cisco world, this is known as
port security.
Introduction to Security Terminology
Hackers find out about vulnerabilities in the software and hardware devices
we use by purposely testing the limitations of the device or software. Once
they discover the vulnerability, they work on figuring out how they can
exploit it.
An exploit takes advantage of a weakness, or vulnerability, in a piece of
software or a device. For example, years ago it was found that most Web
servers were vulnerable to attack because the Web server did not verify the
file being requested in a URL. Hackers exploited this by starting to send commands in a URL that would navigate the folder structure of the Web server
and call for files other than normal Web pages. This is known as folder traversing, and it was a popular exploit on Web servers.
What about CIA?
When working in the security field, you will most likely run into the terms
confidentiality, integrity, availability (CIA). These are the fundamental goals of
security, and ultimately, every security control that we put in place satisfies
one of the elements of CIA.
Confidentiality is the concept of keeping information secret. In order to
implement confidentiality, you may look to securing data with permissions,
but you also have to look at encrypting the information that is stored on disk
or travels across the network.
Integrity is the veracity of the data. Data integrity is about ensuring that when
you receive information, it is the information that was actually sent and not
something that was modified in transit. Hashing is one of the popular methods
of ensuring data integrity. With hashing, the data sender runs the data
through a mathematical algorithm (known as a hashing algorithm), and an
answer is created. When the recipient receives the information, she runs the
data on the same algorithm to see if she gets the same mathematical answer.
If the same answer is calculated, she knows that the data has not been
altered in transit.
Availability is the concept that the data stored on the network is always
accessible to the people who want the data — the people who are authorized
to access it, that is. As security professionals, we need to ensure the availability
Identifying Types of Attacks
of the data, and there are a number of ways to ensure availability. For
example, you can do backups, use RAID volumes for storing your data, and
implement high-availability solutions such as clustering technologies (multiple
servers running the same application, or service, so if one server fails the
request for the service is sent to the second server).
Identifying Types of Attacks
Now that you are familiar with some basic network security terms, let’s talk
about some popular attacks against businesses today. These attacks may
sometimes seem far-fetched, but in reality, they happen every day! This
section outlines some of the most popular types of attacks that can happen
in today’s networking environments.
For the CCENT certification exam, it is critical that you are familiar with the
different types of attacks covered in this section. You are sure to get a few
questions about types of attacks.
To me, a hacker is someone with the technical expertise to bypass the
security of a network or a system. A hacker knows how to use features of a
piece of software or hardware to gain access to restricted areas of a network
and then use those features against you and your system. For example, an
e-commerce Web site connects to a product database behind the scenes so
that you can get a list of products when you visit the site. A hacker knows
how to input data into the site to manipulate the database server into
executing the code that the hacker wants to execute — and this happens
because the hacker understands the technologies used behind the scenes.
There are two major types of hackers:
✦ Black-hat hackers: Break into a system or network for malicious reasons
or for personal gain. The black-hat hacker could be looking for financial
gain, bragging rights, or revenge.
Hackers use a number of different types of attacks to hack into a network,
device, or a system. Sometimes an attack lays the groundwork for a future
or different type of attack: That is, the initial attack does not seem all that
dangerous, but it is used in the future to gain unauthorized access.
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✦ White-hat hackers: Try to hack into software or hardware in order to
understand how to protect others from black-hat hackers. These are the
good guys.
Identifying Types of Attacks
Social engineering attacks
A social engineering attack occurs when a hacker tries to obtain information
or gain access to a system through social contact with a user. Typically, the
hacker poses as someone else and tries to trick a user into divulging personal
or corporate information that allows the hacker access to a system or network.
For example, a hacker calls your company’s phone number, listed in the
phone book, and poses as a technical support person for your company.
He tells the user who answers the phone that a new application has been
deployed on the network, and for the application to work, the user’s password
must be reset. After the password is reset to what the hacker wants, he
might “verify” with the user the credential that the user uses. A user who
is not educated on social engineering might divulge important information
without thinking that the caller might have malicious intent.
A social engineering attack is an attack where a hacker tries to trick a user
or administrator into divulging sensitive information through social contact.
After the sensitive information is obtained, the hacker can then use that
information to compromise the system or network.
This example might sound unrealistic, but it happens all the time. If you
work for a small company, you might not experience a social engineering
attack. In a large corporate environment, though, it is extremely possible
that a social engineering attack would be successful if the company does not
educate its users. A large company usually stations the IT staff or management
at the head office, but employees in most branch locations have never talked
to IT management. The branch employees would not recognize the voices of
the IT folks, so a hacker could impersonate someone from the head office —
and the user at the branch office would never know the difference.
There are a number of popular social engineering attack scenarios — and
network administrators are just as likely to be social engineering victims as
“regular” employees, so they need to be aware. Here are some popular social
engineering attack scenarios:
✦ Hacker impersonates an IT administrator. The hacker calls or e-mails an
employee and pretends to be the network administrator. The hacker tricks
the employee into divulging a password or even resetting the password.
✦ Hacker impersonates a user. The hacker calls or e-mails the network
administrator and pretends to be a user who forgot her password,
asking the administrator to reset her password for her.
✦ Hacker e-mails a program to network users. The hacker typically
e-mails all the users on a network, telling them about a security bug in
the OS. He advises users to run the update.exe file attached to the
e-mail. In this example, update.exe is the attack file — it opens the
computer up so that the hacker can access the computer.
Identifying Types of Attacks
When you are working as a network professional, educate your users
never to run a program that has been e-mailed to them. Most software
vendors, such as Microsoft, state that they will never e-mail a program
to a person: Instead, they will e-mail a URL, but it is up to the person to
go to the URL and download the update. A great book to find out more
on the process a hacker employs to compromise a system is Kevin
Beaver’s Hacking For Dummies, 3rd edition (Wiley).
Network-based attacks
A network-based attack uses networking technologies or protocols to
perform the attack, and they are some of the most popular types of attacks
today. The following explains the terminology associated with seven
important network-based attacks.
Ensure that you are familiar with the different types of network-based
attacks for the CCENT certification exam.
Password attacks
A password attack involves the hacker trying to figure out the passwords
for different accounts on a system, or a password that guards a device. The
three major types of password attacks are dictionary attack, hybrid attack,
and brute force attack.
With a dictionary attack, hackers use a program in conjunction with two text
files to automatically try a number of passwords.
✦ One text file contains the most popular user accounts — such as
administrator, admin, and root — found on networks. This file is termed
the user account text file.
✦ The second text file contains a list of all the words in the English
dictionary, and then some. Hackers can also obtain dictionary files for
different languages. This file is termed the dictionary text file or password
list file.
To protect against a dictionary attack, be sure to use strong passwords that
mix letters, numbers, and symbols. This prevents the passwords from being
found in the dictionary. Also, passwords are normally case sensitive, so be
sure to use a mix of both lowercase and uppercase characters. Mixing the
case of a password means a hacker not only has to guess the password but
also the combination of uppercase and lowercase characters.
Network Security
The dictionary attack program then tries to log in with every user account
in the user account text file with every word in the dictionary text file,
attempting to determine the password for the user account.
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Identifying Types of Attacks
Also note that because there are dictionary files for different languages you
should not use words found in any dictionary. This means avoiding not only
English words, but also French, German, Hebrew . . . even Klingon!
A second type of password attack is known as a hybrid password attack. A
hybrid password attack is like a dictionary attack in the sense it uses a dictionary
file, but it also tries variations of the password by placing numbers on the
end of the word and sometimes replacing popular characters. For example,
after the hybrid attack program tries all the passwords in the dictionary file,
it may then try them again by replacing any letter a with @ in the words.
Hackers can also perform a brute force attack. With a brute force attack,
instead of trying to use words from a dictionary file, the hacker uses a
program that tries to figure out your password by mathematically calculating
all potential passwords with a certain length and set of characters. Figure 1-1
shows a popular password-cracking tool known as LC4. Tools like this are great
for network administrators to audit how strong their users’ passwords are.
Figure 1-1:
with LC4.
To protect against dictionary attacks, we use strong passwords, but to
protect against a brute force password attack, we must implement an
account lockout policy, where after three bad logon attempts, the account is
locked and cannot be used.
If you have configured an account lockout policy to protect your account
database, understand that only works if the hacker is connected to your
network and attempting to hack into live systems (known as an online
attack). If the hacker can get a copy of your account database, or hashed
passwords in a configuration file, and take that away with him (known as an
offline attack) then there is no protection against the brute force attack.
Identifying Types of Attacks
Denial of service
Another popular network attack is a denial of service (DoS) attack, which
can come in many forms and is designed to cause a system or network
device to be so busy that it cannot service a real request from a client,
essentially overloading the system or device and shutting it down.
For example, say you have an e-mail server and a hacker attacks the e-mail
server by flooding the server with e-mail messages, causing it to be so busy
that it cannot send any more e-mails. You have been denied the service that
the system was created for.
There are a number of different types of DoS attacks that have come out
over the years, including the following:
✦ Ping of death: The hacker continuously pings your system with oversized packets causing your system to crash.
✦ SYN flood: The hacker performs a partial three-way handshake with
each port on the system. This uses up memory on your system and
eventually crashes the system. The hacker accomplishes this by sending
a SYN message to a number of different ports, but when your system
replies with an ACK/SYN, the hacker does not complete the process
with an ACK. As a result your system holds that partial connection in
memory, waiting for the ACK. For more on the three-way handshake,
SYN, and ACK, see Book I, Chapter 4.
To protect against denial of service attacks, you need to have a firewall (a
piece of software or a hardware device that prevents someone from entering
your system or network) installed, and you should also keep your systems
and devices patched (apply any updates and security fixes).
Spoofing is a type of attack in which a hacker modifies the source address of
a frame or packet. There are three major types of spoofing:
✦ MAC spoofing: The hacker alters the source MAC address of the frame.
✦ E-mail spoofing: The hacker alters the source e-mail address to make
the e-mail look like it came from someone other than the hacker.
An example of a spoof attack is the smurf attack, which is a combination of a
denial of service and spoofing. Here is how it works:
1. The hacker pings a large number of systems but modifies the source
address of the packet so that the ping request looks like it is coming
from a different system.
Network Security
✦ IP spoofing: The hacker alters the source IP address in a packet.
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Identifying Types of Attacks
2. All systems that are pinged reply to the modified source address — an
unsuspecting victim.
3. The victim’s system (most likely a server) receives so many replies to
the ping request that it is overwhelmed with traffic, causing it to be
unable to answer any other request from the network.
To protect against spoof attacks, you can implement encryption and
authentication services on the network.
Eavesdropping attack
An eavesdropping attack occurs when a hacker uses some sort of packet
sniffer program to see all the traffic on the network. Hackers use packet
sniffers to find out login passwords or to monitor activities. Figure 1-2 shows
Microsoft Network Monitor, a program that monitors network traffic by
displaying the contents of the packets.
Figure 1-2:
Monitor to
analyze FTP
logon traffic.
Notice in Figure 1-2 that the highlighted packet (frame 8) shows someone
logging on with a username of administrator; in frame 11, you can see
that this user has typed the password [email protected] In this example, the
hacker now has the username and password of a network account by
eavesdropping on the conversation!
To protect against eavesdrop attacks, you need encrypt network traffic and
physically control who can connect to your network.
Identifying Types of Attacks
A man-in-the-middle attack involves the hacker intercepting the data in
transit, potentially modifying the data, and then forwarding the information
on to the intended recipient. Note that the intended recipient receives the
information, but the hacker sees the information as well.
Man-in-the-middle attacks are popular with wireless networks at coffee
shops today. The hacker poisons the ARP cache of the wireless clients so
that they forward all the traffic to the hacker’s system first, who then forwards
the information onto the Internet. The clients are still surfing the Internet,
but what they do not realize is that they are passing through the hacker’s
laptop first. (And the hacker is typically capturing all the traffic with a
packet sniffer in hopes of capturing user passwords.)
To protect against man-in-the-middle attacks, you need to restrict access to
the network and implement encryption and authentication services on the
Session hijacking
A session hijack is similar to a man-in-the-middle attack, but instead of the
hacker intercepting the data, altering it, and sending it to whomever it was
destined, the hacker simply hijacks the conversation by disconnecting one
of the participants off the network (usually via a denial of service attack) and
then impersonates that person within the conversation. The other party has
no idea that he or she is communicating with someone other than the original
To protect against session hijacking attacks, you need to restrict access to
the network and implement encryption and authentication services on the
Buffer overflow
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A very popular type of attack today is a buffer overflow attack, which involves
the hacker sending more data to a piece of software than the software
expects. The information sent to an application is typically stored in an
area of memory known as a buffer. When more data than expected is sent to
the application, the information is stored in memory beyond the allocated
buffer. It has been found that if a hacker can store information beyond the
allocated buffer, he can run his own code that typically results in a remote
command shell with administrative access. The reason why administrative
access is gained is because the code executes in the context of the user
account associated with the software that was hacked — normally an
administrative account!
Identifying Types of Attacks
To protect against buffer overflow attacks, you need to keep the system,
applications, and devices up to date with patches and security fixes.
Software-based attacks
Just like there are a number of different types of network attacks, there are a
number of software attacks. As you can likely guess, a software attack comes
through software that a user runs. The most popular software attacks are
mentioned in the sections that follow, and you should be familiar with them
for the CCENT certification exam.
SQL injection
A SQL injection attack occurs when the hacker sends Transact SQL
statements (statements that manipulate a database) into an application so
that the application will send those statements to the database server to be
executed. If the application developer does not validate data inputted into
the application, the hacker can modify the data in the underlying database
or even manipulate the system.
A virus is a program that causes harm to your system. Typically, viruses are
spread through e-mails and are included in attachments, such as word
processing documents and spreadsheets. The virus can do any of a number
of things: It can delete files from your system, modify the system configuration,
or e-mail all your contacts in your e-mail software. To prevent viruses, install
antivirus software and do not open any unexpected file attachments that
arrive in your e-mail.
Trojan horse
A Trojan horse is a type of virus that a user is typically tricked into running
on the system, and when the software runs, it does something totally
different from what the user expected it to do. For example, NetBus (an
older Trojan horse virus) is an example of a Trojan horse virus sent as a file
called patch.exe. The user receiving the file — typically through an e-mail —
believes the file will fix a security issue. The problem is that patch.exe is a
Trojan horse, and when that horse starts running, it opens the computer up
to allow a hacker to connect to the system.
The hacker then uses a client program, like the one shown in Figure 1-3, to
connect to the system and start messing with the computer. The hacker can
do things like launch other programs, flip your screen upside down, eject
your CD-ROM tray, watch your activity, and modify or delete files!
A worm is a virus that does not need to be activated by someone opening the
file. It is self-replicating, meaning that it spreads itself from system to system
Looking at Security Devices
automatically, infecting each computer. How the virus spreads depends on
the virus itself — there have been worm viruses that connect across the
network automatically to a vulnerable system and then infect that system.
Recently, worm viruses automatically infect a flash drive that is connected
to the system so that when you take the drive to the next system, the worm
infects that system from the flash drive.
Figure 1-3:
Using a
Trojan virus
known as
to control
a user’s
Logic bomb
A logic bomb is a type of virus or malicious software that was designed to
wreak havoc on your system on a certain date and time. The scary thing
about logic bombs is that they seem like useful software until the day the
programmer decides it will become malicious!
To protect against malicious software such as a virus, Trojan horse, worm,
and a logic bomb, you need to use a firewall and keep your virus definitions
Looking at Security Devices
A firewall is a piece of software or a device that is designed to control what
traffic is allowed to enter or leave the network. Most firewalls control traffic
that enters the network by analyzing the header of the packet and looking at
the source IP address, destination IP address, and the source and destination
port. If the packet trying to enter the network meets certain conditions, such
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When looking to secure your systems or networks, you can definitely follow
best practices such as patching systems or using strong passwords, but
realistically, you are going to need to use one or more popular security
devices to secure your environment. In this section, I discuss popular security
devices you should be familiar with for the CCENT certification exam.
Looking at Security Devices
as the destination port is 80, the packet is then allowed or denied access to
the network depending on how the firewall is configured.
There are three major types of firewalls that are popular today:
✦ Packet-filtering firewall: A packet-filtering firewall is limited in the sense
that it filters traffic by the fields in the header such as the source and
destination IP address and the source and destination port numbers. It
is very easy for the hacker to bypass this firewall; she can alter the fields
in the header.
✦ Stateful packet inspection firewall: Most firewalls today are stateful
packet inspection firewalls, which filter traffic by the fields in the header
but also can understand the context of the conversation. For example,
a stateful packet inspection firewall knows that before you can send
data to a Web site you must have had a three-way handshake with the
system. The firewall stores the “state” of the conversation in a state
table so it can verify that the packet it is receiving should actually be
occurring at this point in time.
✦ Application-level firewall: An application-level firewall has the benefit
of not only being able to analyze the fields in the header and being
stateful, but it has the added benefit of being able to analyze the
application data that is stored in the packet. For example, an
application-layer firewall can verify that a three-way handshake has
occurred and that the destination port is 80, but it can also verify that
the HTTP command in the packet is a GET and not a POST. These
firewalls can limit what features of an application are allowed to be
There are many different ways to implement a firewall solution, and most
networks use multiple firewalls to control access to different parts of the
network. Figure 1-4 shows a very popular firewall solution that uses two
Figure 1-4:
are used
to protect
the internal
Looking at Security Devices
The first firewall (Firewall1 in Figure 1-4) is connected to the Internet and
controls what traffic is allowed to pass from the Internet through the
firewall. You can see that the first firewall has to allow HTTP traffic and DNS
server traffic through the firewall, as there are public HTTP and DNS servers
behind the first firewall.
The second firewall (Firewall2 in Figure 1-4) is designed to stop all traffic
from passing through that firewall in order to protect the private LAN. The
area between the two firewalls is known as a demilitarized zone (DMZ) and
is designed to allow selected traffic to enter the zone. This firewall solution
is known as a screened-subnet as any traffic that passes into the DMZ is
screened first and ensured it is authorized traffic.
Another very popular firewall solution that relates to Cisco devices is what
is known as a screened-host firewall, shown in Figure 1-5. It is a topology that
has the Internet connected to your router, which will then filter, or screen,
what packets are allowed to pass through and reach the firewall.
Figure 1-5:
A screenedhost firewall
uses a
router to
filter which
reach the
Cisco router
Cisco routers use access lists (a list of rules that determine what packets are
allowed to enter or leave the network) to control what traffic is allowed to
pass through the router. Access lists are beyond the scope of the CCENT
certification but are required knowledge to pass the CCNA certification
An intrusion detection system (IDS) is a device or piece of software that
monitors activity and identifies any suspicious activity on a network
or system. When the IDS identifies the suspicious activity, it logs the
activity and may even send notification to the administrator as an alert.
Network Security
Intrusion detection system
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Looking at Security Devices
There are two main types of intrusion detection systems:
✦ Host-based IDS: This is typically software installed on the system that
monitors activity on that one system. If suspicious activity is found on
the system an alert is generated and the administrator is notified.
✦ Network-based IDS: Monitors network traffic and identifies suspicious
traffic on the entire network, not just one system! The network-based
IDS captures network traffic and then compares that to signatures in the
IDS software. This analysis indicates what type of traffic is considered
What action the IDS takes when suspicious activity is found depends on
what class of intrusion detection system we are talking about. There are two
major classes of intrusion detection systems:
✦ Passive IDS: A passive IDS logs suspicious activity to a file and could
send an alert to the administrator if alerts have been configured. A
passive IDS is normally referred to as just an IDS.
✦ Active IDS: An active IDS logs the suspicious activity, sends an alert to
the administrator, and also takes corrective action such as preventing
the system that is creating the suspicious activity from further accessing
the network.
An active IDS is now known as an intrusion prevention system (IPS).
For the CCENT exam, ensure that you are familiar with the purpose of an intrusion detection system. Also, know the difference between an IDS and an IPS.
I know we talk about switches in detail within Book III, Chapters 3 and 4,
but I want to make sure that I mention switches here as a security device
because switches have some great features that help protect a network
environment. The following are some security features to remember about a
✦ Filtered traffic: The purpose of a switch is to filter traffic by sending the
traffic to only the port where the destination MAC address of the frame
is connected to the switch. This aids in security, as someone else
connected to the switch cannot easily run a packet sniffer and see all
traffic on the network. Because the traffic is not sent to the port of the
person doing the sniffing, there is no opportunity for that person to
capture and view network traffic.
✦ Port security: Port security is the feature on a switch that allows you to
limit which systems can connect to which ports on the switch. With port
security, you associate the MAC address of a system with the port, and
no other system can connect to that port.
Looking at Security Devices
✦ Disable ports: For security reasons, you need to disable any ports on
the switch that you are not using. This prevents someone from connecting
an unknown system to the network without your knowledge.
✦ VLANs: Virtual LANs allow you to create communication boundaries on
the switch. You can create multiple VLANs on the switch and then place
different ports into different VLANs. Systems that are connected to ports
in one VLAN cannot communicate with systems in another VLAN without
the use of a router.
You find out how to configure security features of Cisco switches in the next
Virtual Private Networks
The final security technology I want to mention is what is known as a virtual
private network, or VPN. A VPN is responsible for creating an encrypted
tunnel across an unsecure network such as the Internet. Once the tunnel is
created between the client and the VPN server, any data that is sent through
the tunnel is encrypted.
Looking at Figure 1-6, you see that you are in a hotel room in Toronto and
want to access some files that are in your office in New York. Normally, you
would not try to access those files across the Internet because you would
not want the information sent or received in plain text for someone to
New York
As a solution, you install VPN client software on your laptop, which connects
across the Internet to the VPN server in New York. After the VPN server
authenticates you with your username and password, you are granted
access to the network, and the encrypted tunnel is created. Now any data
sent between the VPN client and the VPN server is secure, as it is encrypted
in transit.
Book IV
Chapter 1
Network Security
Figure 1-6:
creates an
tunnel over
an unsecure
network so
that data
can be
sent and
Your laptop in Toronto
(Hotel room)
Mitigating Security Threats
VPN protocols are responsible for encrypting the data. Examples of VPN
protocols are the Point-to-Point Tunneling Protocol (PPTP) and the Layer 2
Tunneling Protocol (L2TP). Growing in popularity is SSL VPNs, which do not
require VPN client software on the client systems as the Web browser makes
the client connection. It should also be noted that VPNs can be created from
one site to another in order to encrypt all traffic between the two sites (as
opposed to the clients creating the VPN).
Mitigating Security Threats
Now that you have been introduced to some of the different types of
network attacks and identified some of the popular network security
appliances, let’s take a look at how you can minimize potential network
threats. A fancy term for minimizing the threats is mitigating.
Although this section is not intended to be a complete list of the steps to
take to secure your environment, it is definitely a list of some of the
fundamental steps you should take — and they will go a long way to helping
create a secure environment.
To help keep your desktop workstations secure, you should consider doing
the following, at a minimum:
✦ Patch your systems. Be sure to keep your systems up to date with
patches. This includes patching the operating system and all software
✦ Use antivirus software. Ensure that you have company-approved
antivirus software installed on all desktop systems.
✦ Keep virus definitions up to date. Make sure you are keeping the virus
software definitions up to date. These definitions allow the virus-protection
software to know what the current viruses are.
✦ Limit administrative accounts. Do not give all the users administrative
capabilities to the desktop system. Ensure that most users utilize
restricted accounts and limit how many people have administrative
✦ Maintain user awareness. It is important to ensure users are aware of
some of the different threats that exist. Educate users on good e-mail
practices and about social engineering attacks.
To help keep your servers secure you should contemplate doing the
following, at a minimum:
Mitigating Security Threats
✦ Patch systems. Be sure to keep your servers up-to-date with patches.
This includes patching the operating system and all software installed.
✦ Use server-class antivirus software. Ensure that you have
company-approved antivirus software that is designed to run on servers.
✦ Keep virus definitions up-to-date. Make sure that you are keeping the
virus software definitions up-to-date. These definitions allow the
virus-protection software to know what the current viruses are.
✦ Limit administrative accounts. Ensure that you limit how many people
have administrative access to the servers. The more people making
changes to a server, the more chances mistakes will happen.
✦ Configure permissions. Make certain that all the resources are secured
with appropriate permissions.
✦ Place server in a secure room. Be sure that servers are placed in a
locked server room, where access to that room is limited to authorized
✦ Install a firewall. Depending on the type of server, you may decide to
limit what traffic can reach the server by installing a software firewall
on the system. For example, if the system is used only as a Web server,
I recommend installing a software firewall that allows only HTTP and
HTTPS traffic to the system.
To help create a more secure network environment, you should consider
following these general steps, at a minimum:
✦ Encrypt traffic. Depending on how sensitive the information is that
travels on your network, you may decide to encrypt all network traffic.
✦ Use firewalls. Use firewalls to control what type of traffic is allowed to
enter and leave different areas of the network.
✦ Use intrusion detection systems. Be sure to configure an IDS or IPS to
monitor network activity and notify you of any suspicious activity.
✦ Implement device security best practices. Ensure that on your switches
and routers you are following security best practices such as configuring
passwords, encrypting passwords, and using other switch and router
device security concepts mentioned in the next chapter!
Network Security
✦ Place switches and routers in a secure room. Make sure you are
storing switches and routers in a locked server room where you
are limiting access to the room.
Book IV
Chapter 1
Chapter Summary
Chapter Summary
This chapter covers the fundamental concepts regarding network security.
It is an important topic, but understand that this chapter only scratches the
surface of security concepts. For the CCENT certification, be familiar with
the following facts about security:
✦ Authentication is proving your identity to the system.
✦ Authorization is granting someone access to a system or resource after
he has been authenticated.
✦ CIA stands for confidentiality, integrity, and availability.
✦ A social engineering attack is when the hacker tries to trick someone into
compromising security through an e-mail or phone call.
✦ A buffer overflow attack is when the hacker sends too much data to an
application, which normally results in administrative control of the
system in a command shell.
✦ There are three types of password attacks: dictionary, hybrid, and brute
✦ A denial of service (DoS) attack is when a hacker attacks a system or
device by overloading it and causing it to crash or be too busy to perform
its job.
✦ Firewalls control what traffic can enter the network.
✦ An intrusion detection system detects suspicious activity and alerts the
✦ A VPN creates an encrypted tunnel over an unsecure network such as
the Internet.
Lab Exercises
This chapter introduces you to the world of security by exposing you to
some popular security terms and attack types. The following labs help you
review the security concepts discussed in this chapter.
Lab 1-1: Security terminology
In this lab, review basic security terms by matching the term with the
appropriate description.
Lab Exercises
___ Vulnerability
A. Verifying a user’s identity.
___ Packet-filtering firewall
B. Creates an encrypted tunnel over an unsecure
___ Authentication
C. Filters traffic by understanding the context of the
____Mitigating threats
D. A weakness in a piece of software or hardware.
___ CIA
E. An area of the network used to place servers
that are accessed from the Internet.
___ VPN
F. Implementing security controls to minimize the
threats against a system or device.
___ DMZ
G. A device that identifies suspicious activity on a
system or network.
___ Stateful packet inspection
H. The fundamental goals of information security.
___ IDS
I. Inspects the fields in the header of the packet to
decide whether to allow or deny the traffic.
Lab 1-2: Types of attacks
In this lab, review the different types of attacks by matching the term with
the appropriate description.
___ Denial of service
A. Type of malicious software that the user is
tricked into installing; it allows the hacker access to
the system.
___ IP spoofing
B. Capturing network packets and being able to
view information in the packets.
___ Buffer overflow
C. Overloading a system, which results in the
system not being able to perform its job.
___ Eavesdrop attack
D. A type of password attack that tries dictionary
words but also adds numbers to the end of each
___ Social engineering attack
E. A self-replicating virus.
___ MAC spoofing
F. Sending too much data input to an application.
___ Trojan virus
G. Altering the layer-3 source address of a packet.
___ Hybrid attack
H. Altering the layer-2 source address of a packet.
___ Worm virus
I. A hacker tries to trick you into compromising
security through social contact.
Book IV
Chapter 1
Network Security
Network Security Terminology
Prep Test
What type of firewall can allow or deny traffic after inspecting the application
data in the packet?
SYN flood
Spoof attack
Brute force attack
Ping of death
Private LAN
Internal LAN
What type of attack involves the hacker contacting the victim through e-mail or
a phone call?
What is the term used for the area of the network where you are to place
servers from the Internet?
Application-level firewall
Stateful packet inspection firewall
Personal firewall
Packet-filtering firewall
Which of the following is a form of denial of service attack? (Select all that
Social engineering attack
Denial of service
E-mail attack
Contact attack
What type of firewall is capable of inspecting the fields found only in the
header of the packet?
Application-level firewall
Stateful packet inspection firewall
Windows firewall
Packet-filtering firewall
What type of attack involves the hacker sending too much data to the application, which normally results in administrative access within a command shell?
Spoof attack
Buffer overflow attack
Social engineering attack
Denial of service attack
Brute force
What type of firewall knows about the context of the conversation and
whether the packet is the right packet at that point in time?
What type of password attack mathematically calculates all possible password
Spoof attack
Buffer overflow attack
Social engineering attack
Denial of service attack
What type of attack involves the hacker modifying the source IP address of a
packet in order to try to bypass the security control?
Spoof firewall
Stateful packet inspection firewall
Screened firewall
Packet-filtering firewall
Which of the following take corrective action when suspicious activity is
detected? (Select two.)
Active IDS
Passive IDS
Network Security Terminology
Network Security Terminology
A. Application-level firewalls can inspect the application-level data, such as what
application command is executing, and either allow or deny that traffic. See
A, D. A SYN flood attack and the ping of death attack were popular denial of
service attacks years back. Review “Denial of service.”
C. The demilitarized zone (DMZ) is where you should place public servers such
as Web and DNS servers. Check out “Firewalls.”
A. A social engineering attack is when the hacker contacts the victim and tries to
trick the individual into compromising security. Peruse “Social engineering
D. A packet-filtering firewall is capable of inspecting only the packet header to
decide if the packet should be allowed or denied. This type of firewall could be
easily tricked with a spoof attack. Take a look at “Firewalls.”
B. A buffer overflow attack involves the hacker sending too much data to the
application, which typically results in administrative access to the system. Peek
at “Buffer overflow.”
A. A spoof attack is when the hacker alters the source address of a packet in
order to bypass a security control such as a firewall or access control list. Look
over “Spoofing.”
C. A brute force attack mathematically calculates all potential password
combinations. Study “Password attacks.”
B. A stateful packet inspection firewall knows the context of the conversation
and the order in which packets should be received. For example, the firewall
knows that you can send data to a Web server without a three-way handshake.
Refer to “Firewalls.”
A, C. An active IDS takes corrective action when suspicious activity is detected.
Active IDSes are now known as intrusion prevention systems (IPS). Examine
“Intrusion detection system.”
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