Reverse Address Resolution Protocol

Reverse Address Resolution Protocol (RARP) is a Link layer protocol used to obtain an IP address for a given link-layer address (such as an Ethernet address).It has been rendered obsolete by Bootstrap Protocol and the more modern Dynamic Host Configuration Protocol, which both support a much greater feature set than RARP.

The primary limitations of RARP are that each MAC address must be manually configured on a central server, and that the protocol only conveys an IP address. This leaves configuration of subnetting, gateways, and other information to other protocols or the user. Another limitation of RARP compared to BOOTP or DHCP is that it is a non-IP protocol. This means that like ARP it cannot be handled by the TCP/IP stack on the client, but is instead implemented separately.

Reverse ARP is the complement of the Address Resolution Protocol.

Protocol Structure - RARP (Reverse Address Resolution Protocol)RARP and ARP has the same structure:

16		32 bit
Hardware Type		Protocol Type
HLen	Plen	Operation
Sender Hardware Address
Sender Protocol Address
Target Hardware Address
Target Protocol Address

• Hardware type - Specifies a hardware interface type for which the sender requires a response.
• Protocol type - Specifies the type of high-level protocol address the sender has supplied.
• Hlen - Hardware address length.
• Plen - Protocol address length.
• Operation - The values are as follows:
• ARP request.
• ARP response.
• RARP request.
• RARP response.
• Dynamic RARP request.
• Dynamic RARP reply.
• Dynamic RARP error.
• InARP request.
• InARP reply.
• Sender hardware address -HLen bytes in length.
• Sender protocol address - PLen bytes in length.
• Target hardware address - HLen bytes in length.
• Target protocol address - PLen bytes in length.