Dynamic NAT

In dynamic NAT, the router dynamically maps inside local addresses to inside global addresses as needed.

An ACL is used to identify which traffic should be translated.

• If the source IP is permitted by the ACL, the source IP will be translated.

• If the source IP is denied by the ACL, the source IP will not be translated.

  • It will not be dropped.

A NAT pool is used to define the available inside global addresses.

Although they are dynamically assigned, the mappings are still one-to-one (one inside local IP address per inside global IP address).

If there aren't enough inside global IP addresses available (= all currently being used), it is called 'NAT pool exhaustion'.

• If a packet from another inside host arrives and needs NAT but there are no available addresses, the router will drop the packet.

• The host will be unable to access outside networks until one of the inside global IP addresses becomes available.

• Dynamic NAT entries will time out automatically if not used, or you can clear them manually.

NAT pool exhaustion