Appendix A - Ethernet Header

Ethernet Header [CISCO03b]

• Preamble
  64 bit preamble is sequence of alternating 1 and 0 for receiver synchronization with signal.
• Destination MAC
  The first six bytes of an Ethernet frame make up the Destination Address. This specifies to which adapter the data frame is being sent. A Destination Address of all ones (111.111.111.111) specifies a Broadcast Message that is read by all receiving Ethernet adapters. The first three bytes of the Destination Address are assigned by the IEEE to the vendor of the adapter and are specific to the vendor.
• Source MAC
  The next six bytes of an Ethernet frame make up the Source Address. The Source Address specifies from which adapter the message originated. Like the Destination Address, the first three bytes specify the vendor of the card.
• Type / Length
  Type is the type of data encapsulated, (e.g. IP, ARP, RARP, etc) 16-bits. Length is the length of the data.
• Options
• Data
  0 - 2312 octets (bytes).
• Frame Check Sum
  Frame Check Sequence (32 bit CRC). Defined in P802.11.