PAT (NAT Overload)

Port Address Translation (PAT) means using PORTS in order to NAT various Inside Local IPs to 1 Inside Global IP.

Step 1: Create an ACL with all the Inside Local addresses:
 (config)#access-list 1 permit 10.2.2.0 0.0.0.7

Step 2: There are 2 ways to configure PAT, described in Steps 2.1 and 2.2:

Step 2.1: 
- Create the Inside Global IP Pool of any addresses from the Link towards the other Router:
 (config)#ip nat pool OVERLOAD 10.1.1.2 10.1.1.2 prefix-length 24

- Configure the NAT Overload with the defined pool:
 (config)#ip nat inside source list 1 pool TASK2 overload

Step 2.2:
Configure the NAT to point to the Interface you need the traffic to go out from:
 (config)#ip nat inside source list 1 interface s0/1/0.21

!!! The system adds "overload" argument:
 (config)#do sh run | i nat inside
  ip nat inside
  ip nat inside source list 1 interface Serial0/1/0.21 overload