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Address Resolution Protocol

  • It is a communication protocol which is used to find the MAC address of a device from it's IP address.

How ARP works

[From Geeks for Geeks]
ARP working

  • In order to send the data to destination, having IP address is necessary but not sufficient; we also need the physical address of the destination machine.
  • ARP is used to get the physical address (MAC address) of destination machine.
  • Before sending the IP packet, the MAC address of destination must be known. If not so, then sender broadcasts the ARP-discovery packet requesting the MAC address of intended destination.
  • Since ARP-discovery is broadcast, every host inside that network will get this message but the packet will be discarded by everyone except that intended receiver host whose IP is associated.
  • Now, this receiver will send a unicast packet with its MAC address (ARP-reply) to the sender of ARP-discovery packet.
  • After the original sender receives the ARP-reply, it updates ARP-cache and start sending unicast message to the destination.
    ARP Working