A TCP/IP utility and Microsoft Windows NT command for viewing and modifying the local Address Resolution Protocol (ARP) cache, which contains recently resolved MAC addresses of Internet Protocol (IP) hosts on the network. When one host on a TCP/IP network wants to communicate with a second host, the first host begins by using the ARP to resolve the IP address of the second host into its associated MAC address. The MAC address is needed for communication to take place over the network.
Typing arp -a displays the MAC addresses of recently resolved IP addresses. A sample display could be
Internet Address Physical Address Type
172.16.8.25 00-20-af-b4-a1-4e dynamic
172.16.8.200 00-40-95-d1-29-6c static
One of these entries is static, meaning the Internet Protocol-to-MAC address mapping has been manually added to the ARP cache using arp –s.
Note: The arp command is only available if TCP/IP is installed on the machine.