Address Resolution Protocol(ARP)

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ARP Means Address Resolution Protocol. its used for Decision of internet Layer Address into data link layer. ARP basically used mapping a network address into Physical Address(MAC Address). ARP has been implemented with mixed network layer and data link layer.

Type of ARP

The ARP Message (“who is X.X.X.X tell Y.Y.Y.Y”, where X.X.X.X and Y.Y.Y.Y are  IP Address’) is send using Ethernet Broadcast, and an Ethernet protocol type of value 0x806. Since it is broadcast, it is received by all systems in the same collision domain.
This is ensures that is the target of the query is connected to the network, it will receive a copy of the query. Only this system responds. The other systems discard the packet silently.
The target system forms an arp response (“X.X.X.X is hh:hh:hh:hh:hh:hh”, where hh:hh:hh:hh:hh:hh is the Ethernet source address of the computer with the IP address of X.X.X.X). This packet is unicast to the address of the computer sending the query (in this case Y.Y.Y.Y). Since the original request also included the hardware address (Ethernet source address) of the requesting computer, this is already known, and doesn’t require another arp message to find this out.

RARP Means Reverse Address Resolution Protocol. The RARP protocol is used to translate hardware interface addresses to protocol(IP Address) addresses.

Host A wants to send data to Host B which is not on that network, Host A sends an ARP to get a MAC address for host B. Router (gateway) replies to Host A with its own MAC address stating itself as destination (something like a proxy roll call when you respond as present to a roll call of your friend), hence when the data is sent to the destination by Host A it would be sending to the gateway (as destination MAC is given as Gateway’s MAC) which would in-turn send to host B. This is called proxy arp.

Gratuitous ARP
GARP Means Gratuitous Address Resolution Protocol. GARP the Src. host sends and arp request using destination address and source address as its own address and broadcasts mainly used to update other devices about its own IP address.

GARP is used in:
Change of L2 address
Duplicate address detection
Virtual IP

IARP means Inverse Address Resolution Protocol. Its basically used Frame Relay and ATM Network. IARP translates Layer 2 addresses to Layer 3 addresses.

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