ARP resolves an IPv4 address to a MAC address on a LAN. ARP is one of the three main network layer protocols that includes ARP, IPv4, and ICMP, all of which are essential in delivering data.
In the following diagram, we see that ARP is actually in between layer 3 and layer 2, as ARP resolves an IP address (network layer) to a MAC address (data link layer). However, many consider ARP as a layer 3 protocol:
The OSI model: network layer
Now that you can see where ARP resides in the OSI model, let's look at what happens within a LAN and how ARP does its job.