The Request

Sender and Target Fields

The request carries the sender pair and the target IP address whose MAC is being asked for.

highlighted = computed this step

The addresses say who asks

After the fixed header, ARP carries a sender pair and a target pair. The sender pair names the client that is asking.

sender MAC=0x001122334455\text{sender MAC}=0x001122334455
Sender and targetThe ARP payload fields are decoded from the same pinned request frame.Sender and target224 bits / 28 bytes0x0001080006040001001122334455c0a8010a000000000000c0a80101byte 0byte 1byte 2byte 300000000000000010000100000000000byte 4byte 5byte 6byte 700000110000001000000000000000001byte 8byte 9byte 10byte 1100000000000100010010001000110011byte 12byte 13byte 14byte 1501000100010101011100000010101000byte 16byte 17byte 18byte 1900000001000010100000000000000000byte 20byte 21byte 22byte 2300000000000000000000000000000000byte 24byte 25byte 26byte 2711000000101010000000000100000001htype1ptype0x0800hlen6plen4opcode1sender-mac0x001122334455(cont.)sender-ip192.168.1.10(cont.)(cont.)target-mac0x000000000000target-ip192.168.1.1

Sender fields

The sender MAC is 0x001122334455 and the sender IP is 192.168.1.10.

sender IP=192.168.1.10\text{sender IP}=192.168.1.10
Sender and targetThe ARP payload fields are decoded from the same pinned request frame.Sender and target224 bits / 28 bytes0x0001080006040001001122334455c0a8010a000000000000c0a80101byte 0byte 1byte 2byte 300000000000000010000100000000000byte 4byte 5byte 6byte 700000110000001000000000000000001byte 8byte 9byte 10byte 1100000000000100010010001000110011byte 12byte 13byte 14byte 1501000100010101011100000010101000byte 16byte 17byte 18byte 1900000001000010100000000000000000byte 20byte 21byte 22byte 2300000000000000000000000000000000byte 24byte 25byte 26byte 2711000000101010000000000100000001htype1ptype0x0800hlen6plen4opcode1sender-mac0x001122334455(cont.)sender-ip192.168.1.10(cont.)(cont.)target-mac0x000000000000target-ip192.168.1.1

Target fields

The target IP is 192.168.1.1. The request is asking for that neighbor's MAC address.

target IP=192.168.1.1\text{target IP}=192.168.1.1
Sender and targetThe ARP payload fields are decoded from the same pinned request frame.Sender and target224 bits / 28 bytes0x0001080006040001001122334455c0a8010a000000000000c0a80101byte 0byte 1byte 2byte 300000000000000010000100000000000byte 4byte 5byte 6byte 700000110000001000000000000000001byte 8byte 9byte 10byte 1100000000000100010010001000110011byte 12byte 13byte 14byte 1501000100010101011100000010101000byte 16byte 17byte 18byte 1900000001000010100000000000000000byte 20byte 21byte 22byte 2300000000000000000000000000000000byte 24byte 25byte 26byte 2711000000101010000000000100000001htype1ptype0x0800hlen6plen4opcode1sender-mac0x001122334455(cont.)sender-ip192.168.1.10(cont.)(cont.)target-mac0x000000000000target-ip192.168.1.1

Summary

An ARP request is a local question: this sender has one IP address and asks for the MAC beside another IP address.

target MAC unknown=0x000000000000\text{target MAC unknown}=0x000000000000
Sender and targetThe ARP payload fields are decoded from the same pinned request frame.Sender and target224 bits / 28 bytes0x0001080006040001001122334455c0a8010a000000000000c0a80101byte 0byte 1byte 2byte 300000000000000010000100000000000byte 4byte 5byte 6byte 700000110000001000000000000000001byte 8byte 9byte 10byte 1100000000000100010010001000110011byte 12byte 13byte 14byte 1501000100010101011100000010101000byte 16byte 17byte 18byte 1900000001000010100000000000000000byte 20byte 21byte 22byte 2300000000000000000000000000000000byte 24byte 25byte 26byte 2711000000101010000000000100000001htype1ptype0x0800hlen6plen4opcode1sender-mac0x001122334455(cont.)sender-ip192.168.1.10(cont.)(cont.)target-mac0x000000000000target-ip192.168.1.1