RARP (Reverse Address Resolution Protocol) allows a physical machine in a local area network to request its IP address from a gateway server"s Address Resolution Protocol (ARP) table or cache. A network administrator creates a table in a local area network"s gateway router that maps the physical machine (or Media Access Control - MAC address) addresses to corresponding Internet Protocol addresses (IP address). When a new machine is set up, its RARP client program requests from the RARP server on the router to be sent its IP address. Assuming that an entry has been set up in the router table, the RARP server will return the IP address to the machine which can store it for future use.

RARP is available for Ethernet, Fiber Distributed-Data Interface , and Token Ring LANs. ARP (Address Resolution Protocol) performs the opposite function as the RARP: mapping of an IP address to a physical machine address.

Protocol Structure

RARP and ARP has the same structure:

• 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:
  1 ARP request.
  2 ARP response.
  3 RARP request.
  4 RARP response.
  5 Dynamic RARP request.
  6 Dynamic RARP reply.
  7 Dynamic RARP error.
  8 InARP request.
  9 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.

Related Terms: RARP

Sponsor Source: RARP is defined by IETF (http://www.ietf.org) in RFC 903.

Reference: http://www.javvin.com/protocol/rfc903.pdf: Reverse Address Resolution Protocol