Reverse Address Resolution Protocol

Reverse Address Resolution Protocol (RARP) is a network protocol used in telecommunications to map a MAC address to an IP address. RARP plays a crucial role in facilitating communication between devices on a network by allowing them to identify each other based on their unique addresses. By utilizing RARP, telecom operators in the UK can streamline network management, enhance security, and improve overall network efficiency.

The Reverse Address Resolution Protocol (RARP) is closely related to the more widely known Address Resolution Protocol (ARP). While ARP maps an IP address to a MAC address (Media Access Control), RARP does the opposite—translating a device’s hardware address into its corresponding IP address. This reverse mapping is especially useful for network devices such as diskless workstations or network printers that may not know their own IP address upon startup. In such cases, the device sends a RARP request as a broadcast message on the local area network (LAN), asking a RARP server to provide its unique IP address.

A typical RARP packet contains fields such as the protocol address length, hardware address length, and the receiver hardware address fields, which allow devices on the same physical network to understand and process the request. The requesting client broadcasts this information, and the RARP server replies with the correct IP configuration, ensuring that the device can then participate in the internet protocol (IP) environment. This process occurs at the data link layer of the OSI model, making RARP a fundamental network protocol for basic device configuration in early local networks.

However, in modern networks, RARP has become largely obsolete due to its drawbacks and the alternatives that exist. Protocols like the Bootstrap Protocol (BOOTP) and later the Dynamic Host Configuration Protocol (DHCP) replaced RARP because they provide more robust features such as subnet mask assignment, configuration files, and support for multiple subnets. These advanced protocols reduced IP conflicts, supported manual assignment, and worked across broader environments rather than being limited to the same LAN. While RARP is rarely used today, understanding it remains valuable for network administrators when studying legacy devices, troubleshooting address resolution issues, or learning about the evolution of network configuration.