Operation Manual – ARPH3C S9500 Series Routing Switches Chapter 1 ARP Configuration1-1Chapter 1 ARP ConfigurationWhen configuring ARP, go to these sections for information you are interested in:z Introduction to ARPz Configuring ARPz Displaying and Debugging ARP1.1 Introduction to ARPAddress resolution protocol (ARP) is used to resolve an IP address into a MACaddress.I. Why ARPAn IP address cannot be directly used for communication on an Ethernet becausenetwork devices can identify only MAC addresses. An IP address is a network layeraddress. To send datagrams through the network layer to the destination host, the MACaddress of the host is required. Therefore, the IP address must be resolved into a MACaddress.II. ARP address resolution processFigure 1-1 ARP address resolution processSuppose that Host A and Host B are on the same subnet and Host A sends a packet toHost B. The resolution process is as follows:1) Host A checks its ARP table to see whether there is an ARP entry for Host B. If yes,Host A uses the MAC address in the entry to encapsulate the IP packet into a datalink layer frame and sends the frame to Host B.2) If Host A finds no entry for Host B, Host A buffers the packet and broadcasts anARP request, in which the sender IP address and sender MAC address arerespectively the IP address and MAC address of Host A and the target IP address
