ARP-RARP protocol
This page covers ARP and RARP protocol basics with example of fields carried in ARP Request and ARP Response message.
This tutorial covers everything one like to know about networking basics including circuit switching vs packet switching, TCP/IP protocol fields, ARP/RARP protocol fields, what is IP address ,what is MAC address, networking devices which include hub, switch, bridge, router, gateway and firewall.
• Circuit Switching vs Packet switching
• LAN vs WAN vs MAN
• What is an IP address
• What is MAC Address
• Basics of OSI and TCP-IP Layers
• What is Hub
• What is Switch
• What is Bridge
• What is Router
• What is Gateway
• Firewall basics
• TCP-IP Packet format
• ARP Protocol format
ARP is Address Resolution Protocol mainly used to determine ethernet address if IP address is known for a node in the network. RARP does reverse of the ARP protocol, it determines IP address if ethernet address is known. Following table mentions ARP protocol fields for ARP request and ARP response. ARP request is the broadcast packet sent to all the PCs. PC whose IP address matches with the one sent in the broadcast packet will respond back to the source PC of the packet with its ethernet address as needed.
| Byte position | Description | ARP Request(Received)-Hex | ARP Response(Transmitted)-Hex |
| 1 2 3 4 5 6 |
Broadcast address(ARP REQ) Ethernet destination add(ARP RES) |
FF FF FF FF FF FF |
00 A0 C9 22 89 56 |
| 7 8 9 10 11 12 |
Source Ethernet address | 00 A0 C9 22 89 56 |
00 A0 C9 E7 31 45 |
| 13 14 |
Type field | 08 06 |
08 06 |
| 15 16 |
Ethernet | 00 01 |
00 01 |
| 17 18 |
Protocol type | 08 00 |
08 00 |
| 19 | HA length | 06 | 06 |
| 20 | PA length | 04 | 04 |
| 21 22 |
Operation 1 ARP REQ Operation 2 ARP RES |
00 01 |
00 02 |
| 23 24 25 26 27 28 |
Sender Ethernet address | 00 A0 C9 22 89 56 |
00 A0 C9 E7 31 45 |
| 29 30 31 32 |
Sender protocol address | AC 12 02 47 |
AC 12 02 3F |
| 33 34 35 36 37 38 |
Target Ethernet address | 00 00 00 00 00 00 |
00 A0 C9 22 89 56 |
| 39 40 41 42 |
Target Protocol address | AC 12 02 3F |
AC 12 02 47 |
| 43 to 60 | PAD | 7E(all bytes,can be any other field also) | 7E(all bytes) |
Networking related links
What is Bridge
What is Router
What is Gateway
Firewall basics
TCP-IP Packet format
Difference between OSI and TCPIP layers
Difference between TCP UDP