Table of Contents Proxy-ARP Concept
TCP/IP Tutorial and Technical Overview

2.9 Reverse Address Resolution Protocol (RARP)

Figure: Reverse Address Resolution Protocol (RARP)

2.9.1 RARP Overview

The RARP protocol is a network-specific standard protocol. Its status is elective.

Some network hosts, such as diskless workstations, do not know their own IP address when they are booted. To determine their own IP address, they use a mechanism similar to ARP (Address Resolution Protocol), but now the hardware address of the host is the known parameter, and the IP address the queried parameter. It differs more fundamentally from ARP in the fact that a "RARP server" must exist on the network which maintains a database of mappings from hardware address to protocol address.

2.9.2 RARP Concept

The reverse address resolution is performed the same way as the ARP address resolution. The same packet format (see Figure - ARP Request/Reply Packet) is used as for ARP.

An exception is the "operation code" field which now takes the following values:

for the RARP request
for the RARP reply
And of course, the "physical" header of the frame will now indicate RARP as the higher-level protocol (8035 hex) instead of ARP (0806 hex) or IP (0800 hex) in the EtherType field. Some differences arise from the concept of RARP itself:

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