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> 0.0.0.255 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 126.96.36.199 but you want to have a different IP address like 188.8.131.52 then you can use the command.
ip access-list extended natlist-vlan21 permit ip 184.108.40.206 0.0.0.255 any ip nat pool nat-vlan21 220.127.116.11 18.104.22.168 prefix-length 29 ip nat inside source list natlist-vlan21 pool nat-vlan21 overload