The Reverse Address Resolution Protocol (RARP) is a network protocol used to allow a physical machine on a local area network (LAN) to request and obtain its IP address from a gateway server. This process occurs through the gateway’s Address Resolution Protocol (ARP) table or cache.

How RARP Works

Creating the ARP Table

A network administrator creates a table in the LAN’s gateway router that associates the physical addresses of machines (MAC addresses – Media Access Control) with their corresponding IP addresses. This table is essential for RARP to function, as it allows each physical device to be mapped to a specific network address.

Requesting the IP Address

When a new machine is configured, the RARP client program on the machine sends a request to the RARP server located on the router. The request consists of sending the machine’s MAC address, asking for the corresponding IP address in return.

RARP Server Response

Assuming there is an entry in the router’s table corresponding to the provided MAC address, the RARP server returns the IP address to the requesting machine. The machine can then store the IP address for future use.

Uses of RARP

RARP was widely used in the past to configure IP addresses on devices without non-volatile memory (such as older workstations or diskless terminals), which could not store network configurations between reboots. In these cases, every time the device was restarted, it would use RARP to obtain its IP address again.

Limitations of RARP

Despite its utility, RARP has some limitations:

• Manual Configuration: It requires the network administrator to manually configure the MAC and IP address table in the router, which can be laborious in large networks.
• Replacement by Modern Protocols: More modern protocols such as DHCP (Dynamic Host Configuration Protocol) have replaced RARP, offering greater flexibility and automatic IP address assignment features without the need for manual configuration.

Conclusion

The Reverse Address Resolution Protocol was a fundamental element in local networks for configuring IP addresses on devices lacking persistent memory. Although it has been largely replaced today by more advanced protocols, RARP remains an important part of the history of computer networking and its configuration.