Ethernet Information

Ethernet Protocol

Here is the diagram of ethernet PDU. The length of each field is shown in bits. 

Preamble: 8 bytes.
Indicates that the frame is about to begin

Destination Address: 6 bytes.
MAC address of the destination node. May be unicast, multicast or broadcast.

Source Address: 6 bytes.
The unicast MAC address of the source node.

Type/Length: 2 bytes.
The number of bytes encapsulated OR the protocol type of the next higher protocol.

Data: Variable length, 46 to 1500 bytes.

FCS: Frame Check Sequence.

Ethernet Version 2 (also Version "II") is the original version also known as DIX, which stands for Digital, Intel, and Xerox, the vendor consortium who first created it. The IEEE 802.3 Ethernet standard was established some time later. The original Ethernet Version 2 frame varies slightly from the 802.3 Ethernet frame format in that a Type field, also referred to as Ethertype, is used in place of the Length field (also 2 bytes). The Type field is used to "steer" the information up the protocol stack to the next layer. Examples of Ethertype values are 0x0800 for IP and 0x0806 for Address Resolution Protocol (ARP). The 802.3 Ethernet frame has a Length field instead of a Type field, and an 802.2 LLC header in the payload field. The LLC header DSAP field indicates the protocol being carried and steers the frame to the appropriate process in the Network Layer, just as the EtherType field did in the Ethernet Version 2 frame. Another way of looking at this is that Ethernet frames have either a Length or a Type field. When using LLC, the field is Length-encoded. If not using LLC, the field is Type-encoded.

Jumbo Frame

Usually Jumbo Frame is made up of 9000 bytes (payload), 9018 bytes (including header).

pitfalls: DONT_FRAGMENT bit in IP header
solution: Station reconfigure its IP protocol stack for a smaller MTU

Ethernet Standards

IEEE 802.3 half-duplex Ethernet (CSMA/CD)IEEE 802.3x full-duplex Ethernet - PAUSE frame

IEEE 802.3u Fast Ethernet (100BASE-T)
IEEE 802.3z Gigabit Ethernet (1000BASE-X)
IEEE 802.3ab Gigabit Ethernet (1000BASE-T)
IEEE 802.3ac Ethernet VLANs
IEEE 802.3ae 10Gigabit Ethernet
TCP offload - shifting TCP/IP processing tasks to network adapters, removing server CPU out of I/O processing
TCP segment offloading (TSO) - offloading segmentation task of TCP layer from host CPU to NIC

How ICMP Packet is embedded in Ethernet Frame

The 14-byte ethernet header is omitted in this picture. The rest of the fields are:

8 Bytes LLC Header (including SNAP header)
20 Bytes IP Header
8 Bytes ICMP Header
56 Bytes ICMP Payload
4 bytes FCS

How 802.1X Packet is embedded in WiFi Mac Frame

This show an 802.1X packet in 802.11 radio link.

Ethernet Pinout

Here is the RJ-45 Receptacle Pinouts:

Pin  Description
1    TxD+
2    TxD-
3    RxD+
6    RxD-

Here are instructions for building an Ethernet 10BaseT or 100BaseT crossover cable. The pinouts for an Ethernet crossover cable are as follows:

Connector 1 Connector 2 Pinout Pinout 1 3 2 6 3 1 4 OPEN 5 OPEN 6 2 7 OPEN 8 OPEN

  So pin 1 -> pin 3, pin 2 -> pin 6, pin 3 -> pin 1, and pin 6 -> pin 2. All of the other pins are left open.

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First Created: March 4, 2005
Last Modified: May 29, 2006