Currently our Cisco 1721 is configured with a NAT pool using our five public IP addresses. We want to change the IP address on the FastEthernet0 int. from a private IP to a Public IP then connect our firewall to this interface. I've deleted the NAT pool, removed all NAT configuration and attempted to assign a public IP address to the FastEthernet0 interface. When I do I receive the error "IP Overlaps with Serial0". I tried assigning several different IP addresses from our block of IP's but continue to receive the same message.