ARP (Address Resolution Protocol) | RARP (Reverse Address Resolution Protocol) | IARP (Inverse ARP) | What is ARP, RARP, IARP | ARP Commands

ARP (Adress Resolution Protocol )

ARP is that protocol used by an IP address for mapping an IP address to its hardware. ARP works on the data link layer of an OSI Model. Data link layer operates below the network layer of an OSI Model.

Basically what ARP does is that its helps to find out the computer physical address using an IP Address. Every network device has its ARP cache and when a packet has arrived to the destination, on gateway its check the destination from the ARP cache or send a fresh request for ARP, once the address confirmed the packet handed over to the destination.

ARP updates the cache for its future reference. ARP updates the MAC Address as well as IP Addresses in the ARP cache.

once u type a command on your windows computer for arp cache it will display as below.

RARP (Reverse Address Resolution Protocol)

When you have the Mac Address of the host but don't have the IP address then its dynamically used to receives an IP address based on the Mac Address.

IARP (Inverse ARP) 

IARP is used in frame-relay. Conceptually it's identical to RARP; i.e., it's for learning layer 3 addresses when only layer 2 addresses are known. In frame-relay's case the L2 addresses are DLCI's. A router knows it's got a FR circuit plugged into it; and it knows the DLCI for the circuit (either via static configuration or LMI-learned), but it does not know the IP address of the device at the other end of the circuit. And of course it needs to know this address so that when it gets traffic destined for it; it knows which DLCI to send the traffic onto. InvARP therefore sends a query onto the DLCI, the device at the other end responds with its own IP address.