Difference Between ARP (Address Resolution Protocol) and RARP(Reverse Address Resolution Protocol)

Updated: Jan 10, 2022

ARP (Address Resolution Protocol)

It is a network layer protocol. As ARP is a dynamic mapping protocol, each host in the network knows the Logical address of another host. Now, suppose a host needs to send the IP datagram to another host. But, the IP datagram must be encapsulated in a frame so that it can pass through the physical network between sender and receiver.

Here, the sender needs the physical address of the receiver so that it is being identified that to which receiver the packet belong to when the packet travel in the physical network.

For retrieving the physical address of the receiver the sender performs the following action.

The sender sends the ARP query packet on the network which is broadcasted to all the other host or router present in the network.
The ARP query packet contains the logical and physical address of the sender and the logical address of the receiver.
All the host and router receiving the ARP query packet process it but, only the intended receiver identifies its logical address present in the ARP query packet.
The receiver then sends ARP response packet which contains the logical (IP) address and physical address of the receiver.
The ARP response packet is unicast directly to the sender whose physical address is present in the ARP query packet.

RARP (Reverse Address Resolution Protocol)

It is also a network layer protocol. RARP is a TCP/IP protocol that allows any host to obtain its IP address from the server. RARP is adapted from the ARP protocol and it is just reverse of ARP.

RARP perform following steps to obtain an IP address from the server.

The sender broadcast the RARP request to all the other host present in the network.
The RARP request packet contains the physical address of the sender.
All the host receiving the RARP request packet process it but, the authorized host only which can serve RARP service, responds to the RARP request packet such host are known as RARP Server.
The authorized RARP server replies directly to requesting host with the RARP response packet which contains IP address for the sender.

RARP is outdated now because of two reasons. First, the RARP is using the broadcast service of the data-link layer; that means the RARP must be present at each network. Second, RARP only provides IP address but today the computer also need other information.

Difference Between ARP and RARP

ARP RARP

Address Resolution Protocol.	Reverse Address Resolution Protocol.
Retrieves the physical address of the receiver.	Retrieves the logical address for a computer from the server.
ARP maps 32-bit logical (IP) address to 48-bit physical address.	RARP maps 48-bit physical address to 32-bit logical (IP) address.
It is managed and maintained by local host	It is managed or maintained by RARP server
ARP table uses ARP reply for its updation	RARP tables uses RARP reply for configuration of IP Address.
Hosts and routers uses ARP for knowing the MAC address of other hosts and routers in the networks.	While RARP is used by small users having less facilities.
In ARP, broadcast MAC address is used	In RARP, broadcast IP address is used