Communication on an internetwork is accomplished by sending data at layer three using a network layer address, but the actual transmission of that data occurs at layer two using a data link layer address. This means that every device with a fully-specified networking protocol stack will have both a layer two and a layer three address. It is necessary to define some way of being able to link these addresses together. Usually, this is done by taking a network layer address and determining what data link layer address goes with it. This process is called address resolution.

In this section I look at the problem of address resolution at both a conceptual and practical level, with a focus on how it is done in the important TCP/IP protocol suite. I begin with a section that overviews address resolution in general terms and describes the issues involved in the process. I then describe the TCP/IP Address Resolution Protocol (ARP), probably the best-known and most commonly used address resolution technique. I also provide a brief overview of how address resolution is done for multicast addresses in IP, and the method used in the new IP version 6.