4. Packet Format

To communicate mappings from <protocol, address> pairs to 48.bit Ethernet addresses, a packet format that embodies the Address Resolution protocol is needed. The format of the packet follows.

Ethernet transmission layer (not necessarily accessible to the user):

• 48.bit: Ethernet address of destination
• 48.bit: Ethernet address of sender
• 16.bit: Protocol type = ether_type$ADDRESS_RESOLUTION

Ethernet packet data:

• 16.bit: (ar$hrd) Hardware address space (e.g., Ethernet, Packet Radio Net.)
• 16.bit: (ar$pro) Protocol address space. For Ethernet hardware, this is from the set of type fields ether_typ$<protocol>
• 8.bit: (ar$hln) byte length of each hardware address
• 8.bit: (ar$pln) byte length of each protocol address
• 16.bit: (ar$op) opcode (ares_op$REQUEST | ares_op$REPLY)
• nbytes: (ar$sha) Hardware address of sender of this packet, n from the ar$hln field
• mbytes: (ar$spa) Protocol address of sender of this packet, m from the ar$pln field
• nbytes: (ar$tha) Hardware address of target of this packet (if known)
• mbytes: (ar$tpa) Protocol address of target