Configure Cisco Nat on a Cisco 1841 router

For this example I used the following setup

The configuration below is for R2

1. enable
* User Privilege Mode*

2. conf t
*Configuration Mode*

3. interface fa0/0
*Interface fa0/0 configuration mode*
4. ip address dhcp
5. no shutdown
6. ip nat outside
7. exit

*Back in Configuration Mode*
You can share NAT with the other interfaces by placing the ip nat inside commando on them.

8. interface se0/1/0
*Interface se0/1/0 configuration mode*
9. ip address 10.0.5.1 255.255.255.0
10. no shutdown
11. ip nat inside
12. bandwidth 10000000
13. exit

*The bandwidth commando will improve the internet connection between the devices*

14. interface se0/1/1
*Interface se0/1/1 configuration mode*
15. ip address 10.0.6.2 255.255.255.0
16. no shutdown
17. ip nat inside
18. bandwidth 10000000
19. exit

*Back in Configuration Mode*

20. access-list 10 permit 10.0.0.0 0.255.255.255
21. ip nat inside source list 10 interface FastEthernet0/0 overload

If you use OSPF you have to use the  default-information originate commando to share the default route