Cisco

DNS

Add host

cisco# ip host <fqdn> x.x.x.x

DHCP

Clear binding

Source

cisco# clear ip dhcp binding x.x.x.x

Clear ARP entry

Source

cisco# clear ip arp x.x.x.x

Error

Binding already exists

Source

Descriptions: When adding a DHCP reservation the error message appears: A binding already exists for x.x.x.x.
Solution: Currently a client is using the IP address you tried to configure in the binding. Release the dhcp binding first and then add it to the host reservation:

cisco(config)# end
cisco# clear ip dhcp binding x.x.x.x
cisco# conf t
cisco(config)# ip dhcp pool clienta
cisco(dhcp-config)# host x.x.x.x y.y.y.y
cisco(dhcp-config)# hardware-address|client-identifier ffff.ffff.ffff
cisco(dhcp-config)# end