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Port Translation and(or) Redirection using Cisco IOS

Hi There,

I'm facing a "What I thought to be easy" scenario as following:

I have an internal proxy server that listens on multiple ports (80, 443, 21 ...etc) and forwards these requests to an extrenal proxy (outside the network) with the same ports.

The external proxy listens only to one port TCP/3128 and the internal proxy is currently sitting behind a 3Com router that will be replaced with a Cisco 2811 router.

The 3Com is currently changing the destination port in each request that is sent from the internal proxy to the external proxy (bi-directionally). i.e. if the internal proxy IP is and the external IP is x.x.x.x, the request will be:

S IP :

D IP : x.x.x.x

D Port : 80

The 3Com is changing the request to:

S IP :

D IP : x.x.x.x

D Port : 3128

and this applies to any other TCP port such as 443 or 21 or 25.

How to do this on a Cisco IOS router? It sounds very simple but it looks like I'm missing something very silly here.

Help would be highly appreciated.



Re: Port Translation and(or) Redirection using Cisco IOS

Sorry to be the bearer of bad news, but I can't see a way. In IOS you could use a static NAT to redirect one port, but you couldn't map several ports to the same destination port because that would violate the 1:1 nature.

NAT Overview at

Perhaps someone can suggest a way, or else you'll have to change client's proxy ports,

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