To enable NAT on your IOS powered Cisco router, follow these simple steps.
1.) Identify your outside (public) interface. This interface is usually a serial interface, dialer interface, or another ethernet interface.
2.) Identify your inside (private) interface. This is usually ethernet0/0 or fastethernet0/0.
3.) Specify what IP netblock you want to NAT or NAT all subnets.
4.) Enter the configuration and test.
In this example, we use serial0/0 for the "outside" interface and ethernet0/0 for the "inside" interface. We also NAT every IP subnet from the "inside" interface.
router(config)# ! ! Goto your "outside" interface and tell it how to NAT interface serial0/0 ip nat outside exit ! ! Goto your "inside" interface and tell it how to NAT interface ethernet0/0 ip nat inside exit ! ! Build an Access-List to tell the router what subnets to block. access-list 101 permit ip any any ! ! Tell the router to use the new Access-List and to NAT using PAT ip nat inside source list 101 interface Serial0/0 overload exit copy running-config startup-config
Now you are setup to access the Internet with your internal subnets.