PAT Configuration with Packet Tracer

Port-address-translation-pat

PAT Configuration with Cisco Packet Tracer

In some cases there can be hundreds of inside local addresses and at the same time your global ip addresses can be limited.At this time you can use PAT instead of static and dynamic NAT translation.

Here, with PAT(Port Address Translation), we translate each PC to a unique port number of a single public address.

You can DOWNLOAD Packet Tracer example with .pkt format HERE.

Firstly we identify the interfaces as inside and outside as before static and dynamic NAT configurations. Here, we will use the same topology like Dynamic NAT configuration article. Because, for PAT configuration, we need a small change on the configuration.

port address translation (PAT) topology
 

PAT (Port Address Translation) Configuration Topology
Here, we will start with the IP address configurations firstly.

Our PCs on Packet Tracer will be configured with below IP addresses.

PC0 : 10.0.0.2 255.255.255.0 GW:10.0.0.1
PC1 : 10.0.0.3 255.255.255.0 GW:10.0.0.1
PC2 : 10.0.0.4 255.255.255.0 GW:10.0.0.1

Router1(config)# interface FastEthernet0/0
Router1(config-if)# ip address 10.0.0.1 255.255.255.0
Router1(config-if)# no shutdown
Router1(config-if)# exit
Router1(config)# interface FastEthernet0/1
Router1(config-if)# ip address 212.100.100.2 255.255.255.0
Router1(config-if)# no shutdown
Router1(config-if)# exit
Router2(config)# interface FastEthernet0/0
Router2(config-if)# ip address 212.100.100.1 255.255.255.0
Router2(config-if)# no shutdown
Router2(config-if)# exit
Router2(config)# ip default-gateway 212.100.100.2
Router2(config)# no ip routing

Now, let’s do the classical NAT configuration and plus PAT configuration (overload).

Router1 (config)# int e0/0 
Router1 (config-if)# ip nat inside
Router1 (config-if)# exit
Router1 (config)# int s0/0 
Router1 (config-if)# ip nat outside
Router1 (config-if)# exit

After that we will use the below commands for PAT configuration:

Router1 (config)# access-list 10 permit 10.0.0.0 0.0.0.255
Router1 (config)# ip nat pool IPCISCO 50.50.50.80 50.50.50.80 netmask 255.255.255.0
Router1 (config)# ip nat inside source list 10 pool IPCISCO overload

Here, any match interface with access-list 10, will be translated with overload to the serial interface IP address. The secret key word of PAT configuration is “overload“.

Let’s check the nat table on Router1.

Router1# show ip nat translations 
Pro  Inside global     Inside local       Outside local      Outside global
icmp 50.50.50.80:1     10.0.0.4:1         212.100.100.1:1    212.100.100.1:1
icmp 50.50.50.80:2     10.0.0.4:2         212.100.100.1:2    212.100.100.1:2
icmp 50.50.50.80:3     10.0.0.4:3         212.100.100.1:3    212.100.100.1:3
icmp 50.50.50.80:4     10.0.0.4:4         212.100.100.1:4    212.100.100.1:4

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Lesson tags: PAT, NAT
Back to: CCNA > NAT (Network Address Translation)

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