Reverse Address Resolution Protocol(RARP)

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Introduction

RARP stands for “Reverse Address Resolution Protocol”.
RARP is now considered as an old protocol because of use of IPv4 and we use it very less anymore to assign IP addresses to hosts. Now, it has been replaced by BOOTP and later by DHCP.
Reverse ARP differs from the Inverse ARP(InARP), which is designed to obtain the IP address associated with a local Frame Relay data link connection. InARP is not used in Ethernet where as RARP is used in Ethernet.

RARP is a request-response communication protocol used to map or translate the Hardware or Physical or Media Access Control(MAC) address to IP network address.

RARP uses a MAC address to find an IP address .
RARP translates the 48-bit MAC address into 32-bit IPv4 address.
It is one of the most important protocol of Network layer of OSI reference model.
It works when when IPv4 is used.
It uses broadcast in request and unicast in response.
It is a LAN protocol.

On the same network as the hosts, we have a RARP server listening to the RARP requests. This server contains a table that contains the detail of combination of MAC and IP addresses. When it receives a RARP request from a client with its MAC address, it checks & match its table to find the matching IP address for that MAC address in the RARP request packet. The RARP server then replies with a RARP reply to the host through which client is connceted. When the host receives the RARP reply, it knows its IP address.

RARP is used to obtain the IP address of a physical machine in a local area network (LAN) and even diskless workstations(in which workstations broadcast their MAC address in the same/whole LAN network, when the specialized RARP server receives the request it responds the workstation with a unique IP address).