2. Ethernet
Rev. 20170224.114221
2. Ethernet
ccnacookbook.com
Ethernet—The 802.3 family of physical and data link ( layer 2) standards for hard-wired nets. The
same L protocols are used, no matter the physical cable type or transmission speed.
IEEE #
Name
Description
Speed
CABLE & Max Length
802.3
10BASE-T
Ethernet
10 Mbps
Copper, 100 m
802.3 u
100BASE-T
Fast Ethernet
100 Mbps
Copper, 100 m
802.3 z
1000BASE-LX
Gigabit Ethernet
1 Gbps
Fiber, 5000 m
802.3 ab
1000BASE-T
Gigabit Ethernet
1 Gbps
Copper, 100 m
802.3 an
10GBASE-T
10 Gig Ethernet
10 Gbps
Copper, 100 m
Frame—A L data structure including header, data, and trailer.
SOHO (Small Office / Home Office)—i.e. a small network
AP (Access Point)—Wireless network radio for the 802.11 family of standards
L A Y E R
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( P H Y S I C A L )
S T A N D A R D S
UTP (Unshielded Twisted Pair) Pinouts for routers and hosts
RJ-45 Pins
10BASE-T & 100BASE-T
Gigabit
1,2
Send (routers, hosts, wireless APs) or Receive (switches & hubs)
Send, Receive
3,6
Receive (routers, hosts, wireless APs) or Send (switches & hubs)
Send, Receive
4,5
N/C
Send, Receive
7,8
N/C
Send, Receive
Straight-through Cable—Pin 1 goes to pin 1, etc. Good for connecting dissimilar devices, like a
computer to a switch.
Crossover Cable—Connects the pins 1&2 to 3&6 for wiring like devices directly to each other, e.g.
two routers.
Crosstalk—Interference between pairs of wires in the same cable due to EMI (ElectroMagnetic
Interference)
RJ-45—Common name for the connector on  Ethernet cables.
NIC (Network Interface Card)
SPF+ (Small Form-factor Pluggable)—a family of transceivers that can be plugged into generic
ports on Cisco devices to offer flexible media choices.
 (-)

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L A Y E R
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( D A T A
L I N K )
P R O T O C O L S
MAC (Media Access Control) Address—48-bit address used by Ethernet.
OUI (Organizationally Unique Identifier)—24-bit number assigned by IEEE to Ethernet
equipment manufacturers. Used as the first half of a  address, helping to ensure that all
unicast  addresses are unique.
Group (non-unicast) MAC Addresses:
• Broadcast—FFFF.FFFF.FFFF goes to all devices on the 
• Multicast—goes to a subset of devices that have volunteered to receive.
Ethernet Frame
Field
Bytes
Purpose
Preamble
7
Alternating 1s and 0s to set bit-pace
Start of Frame (SOF) Delimiter
1
Announces that the next byte begins the destination address
Destination Address
6
MAC address
Source Address
6
Length
2
Length of the Data field
Data
46-1500
802.2 header and data. Can be padded to meet minimum size
FCS
4
Frame Check Sequence for error detection
Ethertype Field—tells what kind of Layer 3 content is in the payload. Formerly this was in what is
now the length field. Now it is usually in an 802.2 header that is part of the data field.
FCS (Frame Check Sequence) Error Detection—On receipt, if the computed  doesn't match the
one in the frame trailer, the frame is discarded. Upper layer protocols like  can resend the
(now missing) frame to achieve error recovery.
Duplex—With switches, separate pairs can be used for send and receive, allowing full-duplex. Hubs
send and receive on the same pair, forcing half-duplex operation where only one end of the link
can talk at once. Hubs are considered Layer-one devices; they electrically amplify and distribute
a received signal out all other ports without understanding or regenerating it. If you know a hub
is attached to a port on your switch or router, you should force half-duplex operation on that
port.
CSMA/CD (Carrier-Sense Multiple Access / Collision Detection)—Used in half duplex. A Sender:
• Listens until the line is silent
• Begin sending the framework while listening for a collision
• On Collision, all sending nodes:
◦ Send a jamming signal announcing the collision
◦ Back off for a random period of time and begin at the top when time's up
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 (-)
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