(ARP) A method for finding a host's ethernet address from its internet address. The sender broadcasts an ARP packet containing the internet address of another host and waits for it (or some other host) to send back its Ethernet address. Each host maintains a cache of address translations to reduce delay and loading. ARP allows the Internet address to be independent of the Ethernet address but it only works if all hosts support it.

ARP is defined in rfc 826.

The alternative for hosts that do not do ARP is constant mapping.

See also proxy arp, reverse arp.