486 Configuring RoutingARPThe PowerConnect 8024/8024F uses the ARP protocol to associate a layer 2 MAC address with a layer 3IPv4 address. Additionally, the administrator can statically add entries into the ARP table.ARP is a necessary part of the internet protocol (IP) and is used to translate an IP address to a media(MAC) address, defined by a local area network (LAN) such as Ethernet. A station needing to send an IPpacket must learn the MAC address of the IP destination, or of the next hop router, if the destination isnot on the same subnet. This is achieved by broadcasting an ARP request packet, to which the intendedrecipient responds by unicasting an ARP reply containing its MAC address. Once learned, the MACaddress is used in the destination address field of the layer 2 header prepended to the IP packet.The ARP cache is a table maintained locally in each station on a network. There are no specificrequirements for the construction or maintenance of this cache, but at a minimum it needs to containthe information learned from processing ARP protocol packets, which for Ethernet are denoted by an0x0806 EtherType field. ARP cache entries are learned by examining the source information in the ARPpacket payload fields, regardless of whether it is an ARP request or response. Thus, when an ARP requestis broadcast to all stations on a LAN segment or virtual LAN (VLAN), every recipient has the opportunityto store the sender’s IP and MAC address in their respective ARP cache. The ARP response, beingunicast, is normally seen only by the requestor, who stores the sender information in its ARP cache.Newer information always replaces existing content in the ARP cache.The ARP cache can have between 256 and 896 entries When multiple network interfaces are supportedby a device, as is typical of a router, either a single ARP cache is used for all interfaces, or a separate cacheis maintained per interface. While the latter approach is useful when network addressing is not uniqueper interface, this is not the case for Ethernet MAC address assignment so a single ARP cache isemployed.Devices can be moved in a network, which means the IP address that was at one time associated with acertain MAC address is now found using a different MAC, or may have disappeared from the networkaltogether (i.e., it has been reconfigured, disconnected, or powered off). This leads to stale informationin the ARP cache unless entries are updated in reaction to new information seen on the network,periodically refreshed to determine if an address still exists, or removed from the cache if the entry hasnot been identified as a sender of an ARP packet during the course of an ageout interval, usuallyspecified through configuration.The ARP menu page contains links to web pages that configure and display ARP detail. To display thispage, click Routing →ARP in the tree view. Following are the web pages accessible from this menu page:• ARP Create• ARP Table ConfigurationARP CreateUse the ARP Create page to add an entry to the Address Resolution Protocol table.To display the page, click Routing →ARP →ARP Create in the tree view.
