RARP

RARP is the short for Reverse Address Resolution Protocol. It is a TCP/IP protocol that permits a physical address like the Ethernet address, to be translated into an IP address.

The hosts like diskless workstations usually merely know their hardware interface addresses, or MAC address upon booting, however not their IP address.  They must discover their respective IP addresses from an external source, Normally, a RARP server. RARP is defined in RFC 903.