Implementing Physical Layer Solutions
ARP commands

The ARP client and server processes operate on all computers using IP over the Internet. The processes are normally implemented as part of the software driver which drives the NIC.

An end-station will construct an Address Resolution Table when it is connected to a network and attempting to communicate with devices on its LAN segment. To reduce the number of address resolution requests, a client normally caches resolved addresses for a (short) period of time. The ARP cache is of a finite size, and would become full of incomplete and obsolete entries for computers that are not in use if it was allowed to grow without check. The ARP cache is therefore periodically flushed of all entries. This deletes unused entries and frees space in the cache. It also removes any unsuccessful attempts to contact hosts that are not currently running.

The arp command can be used on an end-station to verify that the device is actually communicating with other devices on its LAN segment. The presence of an ARP table indicates that the end-station has at least been connected to the network in the recent past.