What is RARP
Apr 22, 2026
On this article we want to deep diving into RARP. RARP is stands for Reverse Address Resolution protocol it's uses to map a hardware-address(MAC address) to an IP address. The opposite of ARP
dive into What is RARP ? why RARP is used ?
Todays RARP is deprecated and Networks use BOOTP/DHCP
What is inside RARP:
- Hardware Type (Htype 2 Byte)
- Protocol Type (Ptype 2 Byte)
- Hardware address lenght (HLen 1 Byte)
- Protocol address lenght (Plen 1 Byte)
- opcode (2 Byte (03 is for RARP request and 04 is for RARP reply))
- Source Hardware address (SHA 6 Byte for ethernet MAC)
- Source Protocol address (SPA 4 Byte for IPV4)
- Target Hardware address (THA 6 Byte for ethernet MAC)
- Target Protocol address (TPA 4 Byte for IPV4)
- 28 Byte for RARP in Ethernet and IPV4
How RARP works:
- Device boots with only its MAC address.
- Broadcasts a RARP request asking “What is my IP?”
- RARP server looks up the MAC in its table.
- Server replies with RARP reply containing IP.
When RARP is used:
RARP is used for Diskless workstations or devices that boot the os from Network and when this devices boot ask those IP addresses
Why RARP is deprecated:
because this protocol only used for ask IP address without route, gateway, subnetmask or lease time and only in ip layer and its unroutable so after 1990 networks use BOOTP/DHCP
ARP (1979) → RARP (1984) → BOOTP (1988) → DHCP (1993→Now)