Reverse Address Resolution Protocol (RARP) is a protocol used in computer networking, with the primary role of translating physical network addresses (MAC addresses) into IP addresses. RARP is the inverse of the more widely recognized Address Resolution Protocol (ARP), which, conversely, translates IP addresses into MAC addresses.
RARP operates at the data link layer (Layer 2) of the OSI (Open Systems Interconnection) model. RARP’s primary application was to support diskless workstations. These machines do not have a hard disk to store their IP addresses. Therefore, when they start up, they require a mechanism to discover their IP address, and RARP provided a way to achieve this.
When a system boots up and wants to know its IP address, it broadcasts a RARP request packet onto the network. This packet contains its MAC address and requests the corresponding IP address. A RARP server listening on the network responds with the IP address associated with that MAC address.
It’s important to note that RARP requires a server on the network with the MAC-to-IP address mapping. This is in contrast to ARP, where the devices on the network hold their IP-to-MAC address mappings and respond to ARP requests.
RARP is simple and effective, designed for specific use-cases such as diskless workstations. Its use of broadcasting to solicit the required information makes it easy to use and implement in smaller networks.
However, RARP’s simplicity is also its disadvantage. It operates only within a single broadcast domain, which means it doesn’t work well in larger, more complex networks. Furthermore, it requires the maintenance of a RARP server with an up-to-date table of MAC-to-IP address mappings, which adds administrative overhead. Finally, RARP only provides an IP address, leaving other necessary information (like subnet mask, default gateway, and DNS server) to be obtained through other means.
Due to the limitations of RARP, the Bootstrap Protocol (BOOTP) was developed as a more versatile solution. Like RARP, BOOTP provides network booting for diskless workstations. However, it operates at the network layer (Layer 3) of the OSI model and can handle routing, allowing it to function across multiple networks, not just a single broadcast domain.
BOOTP can also carry additional information beyond just an IP address, including subnet mask, default gateway, and the IP address of the BOOTP server. BOOTP is more complicated than RARP, but it provides a more complete solution for network booting requirements.
BOOTP, in turn, laid the foundation for the creation of the Dynamic Host Configuration Protocol (DHCP). DHCP is more sophisticated and flexible than BOOTP. It supports dynamic allocation of IP addresses, reducing the need for manual IP address management, and it can carry a wider range of configuration information.
The Reverse Address Resolution Protocol (RARP) was an essential stepping stone in the evolution of network protocols. Although it is not widely used today, its development was instrumental in refining the methodologies used for address resolution in networked computing. Understanding RARP helps us appreciate the complexities of network communications and the significance of its successors, BOOTP and DHCP, in modern networking.