Ethernet

Ethernet is a network architecture that uses carrier-sense multiple-access with collision detection (CSMA/CD) for controlling access to the network media and baseband broadcasts. Ethernet is based on star topology and works at the data link layer (layer 2 of the OSI network model).

The ethernet standard data encapsulation method is defined by RFC 894. The IEEE 802.3 standard is very similar to Ethernet but does not describe Ethernet as it is used today.

The Ethernet message format consists of:

  • 6 bytes of destination MAC address.
  • 6 bytes of source MAC address.
  • 2 bytes of message type which indicates the type of data being sent.
  • 46 to 1500 bytes of data.
  • 4 bytes of cyclic redundancy check (CRC) information.

Some ethernet message types include:

  • 0800 - IP datagram with length of 38 to 1492 bytes.
  • 0806 - ARP request or reply with 28 bytes and pad bytes that are used to make the frame long enough for the minimum length.
  • 8035 - RARP request or reply of 28 bytes and pad bytes that are used to make the frame long enough for the minimum length.