Networks Horizon

Reverse Address Resolution Protocol (RARP)


RARP is used to obtain the Layer 3 address of the requesting station itself. RARP is now mostly obsolete and replaced by BOOTP, which was later superseded by the Dynamic Host Configuration Protocol (DHCP).

RARP is used by device A to say “I am device A and I am sending this broadcast using my hardware address, can someone please tell me my IP address?”it is providing its own hardware address and asking for an IP address it can use.The response to a request returns the protocol address of the requesting station, not the address of the station receiving the request. IP-specific mechanisms are designed to only support the IP protocol.

Any device on the network that is set up to act as an RARP server responds to the broadcast from the source device. It generates an RARP Reply using an code value of 4. It sets the Sender Hardware Address and Sender Protocol Address to its own hardware and IP address of course, since it is the sender of the reply. It then sets the Target Hardware Address to the hardware address of the original source device. It looks up in a table the hardware address of the source, determines that device's IP address assignment, and puts it into the Target Protocol Address field.

Below are some key point in RARP process.

• Sending device broadcasts the information asking IP address for itself.
• Requester sends RARP Request alongwith source and destination MAC address and leaves Source and destination IP Address field blank.
• All devices ignores the message except RARP server.
• RARP server contains an ARP table with MAC ADDRESS-IP address mapping.
• RARP server send RARP reply which contains an IP address for the requester.
• RARP has been designed to support Internet Protocol(IP) only.