Synatax :
arp <IP> <MAC> arpa
arp x.x.x.x 0000.0000.000 arpa
Example
R1(config)#arp 10.1.1.25 00ac.a1f3.01ab arpa
Notes :
- static ARP entries are more preferred as they are administratively added.
- this way you can ensure that even if you have an ip duplicate the important devices in your network will be always accessible .