Cisco IOS | Nat a subnet to external IP address

It might happen some times that you need to translate a complete subnet to an external IP address. This can be useful if you use multiple companies behind a network device. To accomplish this result you can use on a cisco IOS the following setup.

ip access-list extended natlist-vlan<vlan-tag>
 permit ip <ip range> any

ip nat pool nat-vlan<vlan-tag> <external ip address> <external ip address> prefix-length XX (e.a. 29)
ip nat inside source list natlist-vlan<vlan-tag> pool nat-vlan<vlan-tag> overload

The result will be that a device form the selected subnet will be visible as a different external IP address than the original IP address. For example, your main IP address is but you want to have a different IP address like then you can use the command.

ip access-list extended natlist-vlan21
 permit ip any

ip nat pool nat-vlan21 prefix-length 29
ip nat inside source list natlist-vlan21 pool nat-vlan21 overload

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