For packets to be forwarded across a network from one Cisco 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.
For further information on ARP and configuring static ARP you may wish to refer to:
Cisco Configuring Address Resolution Methods
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