A network engineer is troubleshooting an IPv4 Network Address Translation (NAT) configuration on a Cisco IOS router. The router is configured with NAT overload (PAT) using the command ip nat inside source list 1 interface GigabitEthernet0/0 overload. Inside hosts cannot reach the Internet. The engineer verifies that interface GigabitEthernet0/0 is up and has an IP address, and that access list 1 permits the inside subnet. Which additional configuration is most likely missing?