Cisco Router – Configure NAT (NAT Overload)

KB ID 0000971 


NAT is the process of taking one or more IP adresses and tranlsating it/them into differnet IP addreses. You may require your router to translate all your internal IP addresses to your public (ISP allocated) IP address. To do that we use a process called NAT Overload.

Cisco NAT Overload


1. Connect to the router, and got to enable mode, then global configuration mode.

PetesRouter#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.

2. Setup the WAN (outside facing) interface.

PetesRouter(config)#interface GigabitEthernet0/0
PetesRouter(config-if)#ip address
PetesRouter(config-if)#ip nat outside
PetesRouter(config-if)#no shutdown

3. Setup the LAN (inside facing) interface.

PetesRouter(config)#interface GigabitEthernet0/1
PetesRouter(config-if)#ip address
PetesRouter(config-if)#ip nat inside
PetesRouter(config-if)#no shutdown

4. You will need a ‘default route’ which will be the routers ‘next hop’ towards the internet.

PetesRouter(config)#ip route

5. Create an ACL that wil match any trafic coming from inside (remember permit means match).

PetesRouter(config)#access-list 100 remark NAT-ACL
PetesRouter(config)#access-list 100 permit ip any

6. Then tie it all together with the following command;

PetesRouter(config)#ip nat inside source list 100 interface GigabitEthernet 0/0 overload

7. Save the changes.

PetesRouter#write mem
Building configuration...


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Author: Migrated

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