Operation Manual – ARPH3C S7500 Series Ethernet Switches Chapter 1 ARP Configuration1-3Different manufactures’ products may provide more information about ARP table. Onan S7500 series Ethernet switch, you can use the display arp command to displayARP entries in the table (see ARP Command Manual for details).Table 1-3 describes the fields of APR table.Table 1-3 Description on the fields of an ARP tableField DescriptionIF index Index of the physical interface or port on the device owningthe physical address and IP address in the entryPhysical address Physical address of the device, a MAC addressIP address IP address of the deviceTypeEntry type, which can be:z 1: Not any of the followingz 2: Invalid entryz 3: Dynamic entryz 4: Static entry1.1.4 ARP ImplementationThe ARP table of a host is empty when the host just starts up. When a dynamic ARPentry has not been used for a specific time period, it is removed from the ARP table.The purpose of this is to save memory space and update the entries in the ARP table.The following describes the implementation procedure of ARP.z Suppose Host A and Host B are on the same network segment. The IP address ofHost A is IP_A and that of Host B is IP_B. To send a packet to Host B, Host A firstlooks up its own ARP table for an ARP entry that contains IP_B. If such an entry isfound, Host A encapsulates the IP packet into a frame by using the MAC addressin the entry as the destination MAC address and then sends the frame to Host B.z If no such an entry is found in the ARP table, Host A puts the packet into thetransmission queue, generates an ARP request packet with the IP addresses ofHost B and Host A and the MAC address of Host A (IP_B, IP_A and MAC_A), andbroadcasts the request on the Ethernet. Since the ARP request is broadcasted, allhosts on the network segment receive it. However, only the host with IP addressIP_B (Host B) will process the request further.z Host B adds the sender IP address and MAC address carried in the request (IP_Aand MAC_A of Host A) in an entry to its ARP table and then returns an ARP replypacket to the sender (Host A), with its MAC address carried in the packet. Notethat the ARP reply is a unicast packet instead of a broadcasted packet.z Upon receiving the ARP reply, Host A extracts the IP address and MAC address ofHost B from the packet, adds them in an entry to its ARP table, and then sends outall the packets destined for Host B in the transmission queue.
