IP Routing Primer

ARP Explained

All layer three network protocols must have a method for mapping layer three addresses to their corresponding layer two addresses (typically a MAC address) for point-to-point data transfer. In this case, point-to-point means that only two hosts are participating in the data transfer. The other options, such as point-to-multipoint (Internet television or radio broadcasting) and multipoint-to-multipoint (TCP/IP-based videoconferencing), are beyond the scope of this book.

Consider an IP host that is trying to initiate a TCP/IP application session, such as FTP with another IP host. The initiating host first checks its ARP table (a cache of known IP address/MAC address associations) to see whether it already has the correct MAC address ...