Network hosts such as diskless workstations frequently do not know their protocol addresses when booted; they often know only their hardware interface addresses. To communicate using higher-level protocols like IP, they must discover their protocol address from some external source. Our problem is that there is no standard mechanism for doing so.
Plummer's "Address Resolution Protocol" (ARP)  is designed to solve a complementary problem, resolving a host's hardware address given its protocol address. This RFC proposes a "Reverse Address Resolution Protocol" (RARP). As with ARP, we assume a broadcast medium, such as Ethernet.