Nat is very simple you configure.

Requirements

1 ip nat inside - under an interface (usually the inside ethernet interface)

2 ip nat outside - under an interface (usually the outside serial or ethernet interface)

3 access-list 10 permit 192.168.1.0 0.0.0.255 - an access list to permit your internal network ips to use nat. configure this as your internal ip addresses

4 ip nat inside source list 10 interface (outside interface) - lets say you dont want to waste ip addresses you are going to use PAT. this will have all your internal ips use the outside interface address to route on the internet.

heres an example


ethernet0
ip address 192.168.10.1
ip nat inside

ethernet1
ip address 216.54.100.1
ip nat outside

ip nat inside source list 8 interface ethernet1
access-list 8 permit 192.168.10.0 0.0.0.255