Port Address Translation(PAT) configuration in Packet Tracer

Welcome! In this tutorial, we’ll look at how to configure Port Address Translation (PAT) on a router in Packet Tracer. With PAT technique, one public IP address can be used to translate many private IP addresses for various internal devices (devices in a given private LAN). However,  a different port is assigned to each private IP address. Because many private IP addresses are mapped to one global IP address, PAT is also referred to as NAT overload.

PAT configuration is almost similar to dynamic NAT configuration, only that in PAT, you don’t have to create a pool of public IP addresses because the private addresses can map to just one public IP address. This public address may be the IP address of a router’s interface connecting to the outside networks.

Let’s now do configurations in Packet Tracer.

First build the network topology.

Then configure IP addresses on the router, the two laptops and the internet server.

Router IP configuration

Router(config)#int fa0/0
Router(config-if)#ip add 192.168.1.1  255.255.255.0
Router(config-if)#no shut
Router(config-if)#
Router(config-if)#int fa0/1
Router(config-if)#ip add 200.0.0.1 255.255.255.0
Router(config-if)#no shut

Host IP configurations

Laptop1:  IP add: 192.168.1.2/24    Default gateway: 192.168.1.1

Laptop2:  IP add: 192.168.1.3/24     Default gateway   192.168.1.1

Internet Server:  IP add: 200.0.0.10/24   Default gateway:   200.0.0.1

Now, to configure PAT on the router:

1.  Configure an inside interface on the router using ip nat inside command.

2. Configure an outside interface on the router using ip nat outside command.

3. Create an access-list of private IP addresses to be translated using the command access

4. Enable PAT on the router using the command ip nat inside source list ACL_NUMBER interface INTERFACE_TYPE overload.

Here are the  PAT configuration commands for the router:

Router(config)#int fa0/0
Router(config-if)#ip nat inside
Router(config-if)#

Router(config-if)#int fa0/1
Router(config-if)#ip nat outside
Router(config-if)#exit
Router(config)#access-list 1 permit 192.168.1.2 0.0.0.255
Router(config)#ip nat inside source list 1 int fa0/1 overload

That’s all we have to do for configurations. We’ll now move on to test whether the NAT translations are actually taking place.

To do this:

Ping the internet server from Laptop1, then from Laptop 2. If you hadn’t done that until now, the pings will trigger address translations on the router.

You can verify address translations using the command: show ip nat translations. 

See the results:

From the picture above, you can see that the same public address (outside local) has been used to translate the private addresses (inside local) of the two laptops, but using different port numbers.

Golden Tip: You can create an access list of private IP addresses and a pool of public IP addresses then enable Port Address Translation on a router in a similar way to dynamic NAT configuration. The only difference in configurations between PAT and dynamic NAT  if PAT configuration is done this way is the word overload.

And we are done! That’s it! PAT.

Hope this tutorial was helpful to you. Comment to help improve it.

All the best!

You may also like to read:

• Dynamic NAT configuration
• Static NAT configuration