The Reply

Reply Fills the MAC

The router answers with the MAC address that belongs to the requested local IP address.

highlighted = computed this step

The owner answers directly

The reply is no longer broadcast. The Ethernet destination is the client MAC, and the Ethernet source is the router MAC.

reply opcode=2\text{reply opcode}=2
ARP replyThe reply fills the router MAC and sends the answer back to the client.Reply Ethernet112 bits / 14 bytes0x001122334455aabbccddeeff0806byte 0byte 1byte 2byte 300000000000100010010001000110011byte 4byte 5byte 6byte 701000100010101011010101010111011byte 8byte 9byte 10byte 1111001100110111011110111011111111byte 12byte 130000100000000110dst-mac0x001122334455(cont.)(cont.)src-mac0xaabbccddeeffethertype2054->ARPARP reply224 bits / 28 bytes0x0001080006040002aabbccddeeffc0a80101001122334455c0a8010abyte 0byte 1byte 2byte 300000000000000010000100000000000byte 4byte 5byte 6byte 700000110000001000000000000000010byte 8byte 9byte 10byte 1110101010101110111100110011011101byte 12byte 13byte 14byte 1511101110111111111100000010101000byte 16byte 17byte 18byte 1900000001000000010000000000010001byte 20byte 21byte 22byte 2300100010001100110100010001010101byte 24byte 25byte 26byte 2711000000101010000000000100001010htype1ptype0x0800hlen6plen4opcode2sender-mac0xaabbccddeeff(cont.)sender-ip192.168.1.1(cont.)(cont.)target-mac0x001122334455target-ip192.168.1.10

Reply envelope

The reply destination is 0x001122334455. The reply source is 0xaabbccddeeff.

dst=0x001122334455,src=0xaabbccddeeff\text{dst}=0x001122334455,\quad \text{src}=0xaabbccddeeff
ARP replyThe reply fills the router MAC and sends the answer back to the client.Reply Ethernet112 bits / 14 bytes0x001122334455aabbccddeeff0806byte 0byte 1byte 2byte 300000000000100010010001000110011byte 4byte 5byte 6byte 701000100010101011010101010111011byte 8byte 9byte 10byte 1111001100110111011110111011111111byte 12byte 130000100000000110dst-mac0x001122334455(cont.)(cont.)src-mac0xaabbccddeeffethertype2054->ARPARP reply224 bits / 28 bytes0x0001080006040002aabbccddeeffc0a80101001122334455c0a8010abyte 0byte 1byte 2byte 300000000000000010000100000000000byte 4byte 5byte 6byte 700000110000001000000000000000010byte 8byte 9byte 10byte 1110101010101110111100110011011101byte 12byte 13byte 14byte 1511101110111111111100000010101000byte 16byte 17byte 18byte 1900000001000000010000000000010001byte 20byte 21byte 22byte 2300100010001100110100010001010101byte 24byte 25byte 26byte 2711000000101010000000000100001010htype1ptype0x0800hlen6plen4opcode2sender-mac0xaabbccddeeff(cont.)sender-ip192.168.1.1(cont.)(cont.)target-mac0x001122334455target-ip192.168.1.10

Reply payload

Opcode 2 says this is the answer. Sender MAC 0xaabbccddeeff belongs with sender IP 192.168.1.1.

sender MAC=0xaabbccddeeff\text{sender MAC}=0xaabbccddeeff
ARP replyThe reply fills the router MAC and sends the answer back to the client.Reply Ethernet112 bits / 14 bytes0x001122334455aabbccddeeff0806byte 0byte 1byte 2byte 300000000000100010010001000110011byte 4byte 5byte 6byte 701000100010101011010101010111011byte 8byte 9byte 10byte 1111001100110111011110111011111111byte 12byte 130000100000000110dst-mac0x001122334455(cont.)(cont.)src-mac0xaabbccddeeffethertype2054->ARPARP reply224 bits / 28 bytes0x0001080006040002aabbccddeeffc0a80101001122334455c0a8010abyte 0byte 1byte 2byte 300000000000000010000100000000000byte 4byte 5byte 6byte 700000110000001000000000000000010byte 8byte 9byte 10byte 1110101010101110111100110011011101byte 12byte 13byte 14byte 1511101110111111111100000010101000byte 16byte 17byte 18byte 1900000001000000010000000000010001byte 20byte 21byte 22byte 2300100010001100110100010001010101byte 24byte 25byte 26byte 2711000000101010000000000100001010htype1ptype0x0800hlen6plen4opcode2sender-mac0xaabbccddeeff(cont.)sender-ip192.168.1.1(cont.)(cont.)target-mac0x001122334455target-ip192.168.1.10

Summary

The reply fills the missing neighbor MAC exactly: the router address is now a concrete field in the ARP payload.

router MAC=0xaabbccddeeff\text{router MAC}=0xaabbccddeeff
ARP replyThe reply fills the router MAC and sends the answer back to the client.Reply Ethernet112 bits / 14 bytes0x001122334455aabbccddeeff0806byte 0byte 1byte 2byte 300000000000100010010001000110011byte 4byte 5byte 6byte 701000100010101011010101010111011byte 8byte 9byte 10byte 1111001100110111011110111011111111byte 12byte 130000100000000110dst-mac0x001122334455(cont.)(cont.)src-mac0xaabbccddeeffethertype2054->ARPARP reply224 bits / 28 bytes0x0001080006040002aabbccddeeffc0a80101001122334455c0a8010abyte 0byte 1byte 2byte 300000000000000010000100000000000byte 4byte 5byte 6byte 700000110000001000000000000000010byte 8byte 9byte 10byte 1110101010101110111100110011011101byte 12byte 13byte 14byte 1511101110111111111100000010101000byte 16byte 17byte 18byte 1900000001000000010000000000010001byte 20byte 21byte 22byte 2300100010001100110100010001010101byte 24byte 25byte 26byte 2711000000101010000000000100001010htype1ptype0x0800hlen6plen4opcode2sender-mac0xaabbccddeeff(cont.)sender-ip192.168.1.1(cont.)(cont.)target-mac0x001122334455target-ip192.168.1.10