Address Resolution Protocol (ARP)
ARP is the protocol IPv4 devices use to find the MAC address that matches a known IP address on the local network.
What is Address Resolution Protocol (ARP)?
A device that needs to send a packet to a local IP address broadcasts an ARP request; the owner of that address replies with its MAC address, which is then cached. IPv6 uses Neighbour Discovery instead. Because it links layer 3 addresses to layer 2 addresses, ARP is sometimes described as a "layer 2.5" protocol, but it is most often placed at layer 2.