What is ARP?

Although applications communicate using IP addresses, network adapters actually exchange Ethernet frames using hardware (MAC) addresses.

ARP (Address Resolution Protocol) bridges this gap by translating IP addresses into MAC addresses.

A simplified ARP lookup looks like this:

IP Address > ARP Request > MAC Address

When a computer wants to communicate with another host on the local network, it first checks its ARP cache.

If no matching entry exists, the computer broadcasts an ARP request asking which device owns the specified IP address.

The destination computer replies with its MAC address, and the result is stored in the ARP cache for future use.

On Windows, the current ARP cache can be displayed using:

arp -a

This is a useful command when troubleshooting local network connectivity or duplicate IP address problems.

The ARP protocol is described in RFC 826 document by D. Plummer.