2. ARP, RARP: address resolution protocols

IP addresses are assigned independently of a machine's hardware address. To send a datagram over the Internet, the network software must convert the IP address into a physical address, which is used to transmit the frame. If the physical address is a short integer, it can be easily modified to match the IP machine address. Otherwise, translation must be performed dynamically.

The Address Resolution Protocol (ARP) performs this translation based on the physical network. The ARP protocol enables machines to resolve addresses without using a static table. A machine uses ARP to determine the physical destination address by broadcasting an ARP request on the subnet containing the IP address to be translated. The machine with the IP address in question responds by sending back its physical address. To make ARP more efficient, each machine maintains a table of resolved...