Pooled Network Address Translation

Static Network Address Translation provides a simple one to one method of translating private to public IP addresses. Pooled NAT provides a more dynamic approach to one to one translation when required.

The dynamic translation lasts for at least 24 hours by default when requested by a private IP address. If a one to one translation remains idle for 24 hours, the public IP address will be returned to the dynamic pool to be reused by another private IP address at a later time.

The default timeout can be changed with the command ip nat translation time <seconds>. Existing mappings can be cleared with the command clear ip nat translation *

To configure Pooled Network Address Translation as an inside pooled NAT:

1. Configure outside interfaces with ip nat outside
2. Configure inside interfaces with ip nat inside
3. Create a standard or extended access control list to specify private IP addresses that will be able to utilise the pooled network address translation, for example:
   1. ip access-list standard 10
      1. permit 10.20.40.0 0.0.0.255
4. Create the global pool of IP addreses to be utilised with the command ip nat pool <pool-name> <starting-ip-address> <ending-ip-address> prefix-length <prefix-length>
5. Tie everything together with the command ip nat inside source list <access-list> pool <pool-name>