Previously we have seen how a sender will know the destination's MAC address if the IP address of the receiver is known to the sender .
- RARP is just opposite of ARP.
- RARP stands for Reverse Address Resolution Protocol.
- Sometimes a machine knowns its MAC address but not the IP address so it can know its IP address using RARP.
- RARP maps Physical address to logical address.
A machine can know its MAC address by seeing its NIC card and using RARP request it can know its IP address.
So if a machine wants to know its IP address it broadcast RARP request packets since broadcasting is done data link layer, then there a RARP server is installed at each network which tells the requesting machine's their IP address. Reply form RARP server is a unicast message.
If an administration has a lot of subnet or subnetwork then it has to assign a RARP server for each individual subnetwork which will increase the number of entries in the routing table.