For packets to be forwarded across a network from one device to another, they must be encapsulated in a Layer-2 frame containing the Layer-2 source and destination addresses. Various protocols rely on different mechanisms to resolve a destination Layer-3 address to a destination Layer-2 address. When IP operates over a LAN such as Ethernet, it uses Address Resolution Protocol (ARP) to find the Layer-2 Media Access Control (MAC) address corresponding to the Layer-3 IP address of a device. This mapping is stored in the ARP table. Instead of dynamically mapping the Layer-3 address to a Layer-2 address, Cisco routers can also be configured with a static mapping between the addresses.
To configure a static ARP mapping, issue the arp ip-address hardware-address type [alias] from the global configuration mode of the router. This command installs a permanent entry in the ARP table of the router, while dynamically learned entries are either refreshed or aged out.