The Address Resolution Protocol (ARP) is developed to enable communications on an internetwork and performs a required function in IProuting. ARPlies in the（ ）layer of the TCP/IP model, and allows computers to introduce each other across a network prior to communication. ARP finds the（ ）address ofa host from its known（ ）address.Before a device sends a datagram to another deviceit looks in its ARP cache to see if there is a MAC address and corresponding IP address for the（ ）device.If there is no entry,the device sends a（ ） message to every device on the network.Only the device with the matching IPaddress replies with a packet containing the MAC address for the device(except in the case of “proxy ARP”).