The Address Resolution Protocol(ARP)was developed to enable communication on an Internetwork and perform a required function in IP routing.ARP lies between layers（71）of the OSI model,and allows computers to introduce each other across a network prior to communication.APR finds the（72 ）address of a host from its known（73 ）address.Before a device sends a datagram to another device,it looks in its ARP cache to see if there is a MAC address and corresponding IP address for the destination device.If there is no entry,the souree device sends a（74）message to every device on the network.Each device compares the IP address to its own.Only the device with the matching IP address replies with a packet containing the MAC address for the device（except in the case of “proxy ARP”）.The source device adds the（75 ）device MAC address to its ARP table for future reference.
