ARP is used by the Internet Protocol network layer protocol to map IP network addresses to the hardware addresses used by a DataLink Protocol. A host that needs a physical address broadcasts an ARP request across TCP/IP; to which the host with the physical address responds. An example of its use would be on an Ethernet network to map a 48-bit MAC Address to a 32-bit IP address.
Additional resources
Address Resolution Protocol
More background on ARP.
ARP
How a remote machine differentiates between different media access control addresses of machines on the same subnet by sending out FFFF.FFFF.FFFF for the destination MAC. Network World, 05/27/02.
