Ethernet Frame Structure

Structure of an Ethernet frame

• Sending adapter encapsulates packet in frame
• Preamble: synchronization
  • 7 bytes with pattern 10101010, followed by 1 byte with pattern 10101011
  • Used to synchronize receiver, sender, clock rates
• Addresses: source and destination MAC addresses
  • Adapter passes frame to network-level protocol if destination is local MAC address or broadcast address
  • Otherwise, adapter discards frame
• Type: indicates higher level protocol
  • Usually IP, but also others
• CRC: cyclic redundancy check