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Address Resolution Protocol

Sending IP packets on a multiaccess network requires mapping from an IP address to a MAC address (the physical or hardware address).

In an Ethernet environment, Address Resolution Protocol (ARP) is used to map a MAC address to an IP address. ARP dynamically binds the IP address (the logical address) to the correct MAC address. Before IP unicast packets can be sent, ARP discovers the MAC address used by the Ethernet interface where the IP address is configured.

Hosts that use ARP maintain a cache of discovered Internet-to-Ethernet address mappings to minimize the number of ARP broadcast messages. To keep the cache from growing too large, an entry is removed if it is not used within a certain period of time. Before sending a packet, the host searches its cache for Internet-to-Ethernet address mapping. If the mapping is not found, the host sends an ARP request.

Note: For information about MAC address validation, see MAC Address Validation.

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