ARP - technical definition

The address resolution protocol (see Figure 1-1) is used to find a hardware address for a given IP address. Computer names on the Internet are associated with IP addresses. To send a message to a computer via the local network (for example, through Ethernet or a wireless network), the hardware address must be known.

So, when a computer needs to transmit an IP packet to a computer in the same network segment, it broadcasts the destination IP address on the local Ethernet using the ARP protocol, where it is read by all attached computers. To achieve this, it fills out the fields of the protocol with its Ethernet address, its IP address, and the IP address of the destination, filling the destination IP Address with 1 and signaling that it is requesting the relevant Ethernet address. The computer owning the address then responds, and the IP packet can then be sent to that Ethernet address.

The ARP protocol is designed to serve in a more general fashion; it includes a Hardware Address Type and a Protocol Address Type that can be set according to the higher-level protocolÂ’s needs.

See Also: Ethernet; Internet; Internet Protocol (IP); IP Addresses; Packet; Protocol; TCP/IP or Transmission Control Protocol/Internet Protocol.