Ethernet only deals with MAC addresses. It doesn’t involve any routing or packets. It works with Frames.

Ethernet Frame:

  • Preamble – Start bits
  • Destination (6 bytes) – Destination MAC address
  • Source (6 bytes) – Source MAC address
  • Length/Type (2 bytes) – Length and EtherType
  • Payload (1500 bytes) – Data, zero padded
  • FCS  (4 bytes) -Frame checksum, CRC

The most important part is the EtherType

  • 0x800 – an IP header is next
  • 0x806 – ARP is on the way
  • 0x8035 – RARP is coming
  • 0x810 – this has 801.1q VLAN tags

They can all live in the broadcast domain simultaneously.