Use the following commands to dictate which interface should be defined as the inside and outside.

(config-if)#ip nat inside
(config-if)#ip nat outside 

The access list must permit only those addresses that are to be translated. An access list that is too permissive can lead to unpredictable results. Cisco highly recommends that you do not configure access lists referenced by NAT commands with permit any. Using permit any can result in NAT consuming too many router resources, which can cause network problems.

(config)access-list 1 permit 10.10.0.0 0.0.0.255
(config)#ip nat inside source list 1 interface FastEthernet0/0 overload 

Show/Debug Commands

• show ip nat translations
• debug ip nat
• no debug all