Understanding the role and purpose of ARP

ARP is one of the three main network layer protocols (ARP, IPv4, and Internet Control Message Protocol (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 of the Open Systems Interconnection (OSI) model, as ARP resolves an IP address (network layer) to a MAC address (data link layer):

Figure 16.1 – The OSI model network layer protocols

Note

Although ARP resides in between Layer 2 and Layer 3 of the OSI model, many consider ARP as a Layer 3 protocol.

In this section, we'll see how ARP resolves a MAC address. We'll then learn how the ARP cache helps provide a speedier response. In addition, we'll discover how an IPv6 network uses the Neighbor Discovery Protocol (NDP) to resolve an IPv6 address to a MAC address.

On a LAN using IPv4, the frame header must use a MAC...