NAT with Port Forwarding

NAT port forwarding is typically used to allow remote hosts to connect to a host or server on our private LAN. A host from the Internet will connect to the outside IP address of a router that is configured for NAT. This NAT router will forward traffic to host on the inside. Here is an example:

Above we have three routers, we’ll use these to demonstrate NAT port forwarding. R1 represents an internal Web-Server, where R3 represents user-host on the outside. R2 will make sure that the Web-Server is reachable from the outside using the external IP address.

Configuration :

First we will configure a static route on R1 so it knows how to reach the outside world:

!
R1(config)#ip route 0.0.0.0 0.0.0.0 fa1/0 192.168.12.2
!

Now we can worry about the NAT commands. Let’s configure the inside and outside interfaces:

R2(config)#interface FastEthernet 0/0
R2(config-if)#ip nat inside
!
R2(config)#interface FastEthernet 1/0
R2(config-if)#ip nat outside

Now we should configure the Port forwarding feature using the outside IP address

Example:

When someone try to connect to TCP port 80 on the outside interface of R2, it should be forwarded to R1. Here’s how to do it:

!
R2(config)#ip nat inside source static tcp 192.168.12.1 80 192.168.23.2 80 extendable
!

Useful Links:

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