Strange? NAT behavior on cisco 2651

Posted on 2003-03-29
Medium Priority
Last Modified: 2010-04-17
I'm running 2 private networks(192.168.2.x and 192.168.3.x) off of a cisco 2651 with two ethernet interfaces. I have a full T1 to the internet. I'm using NAT and all works fine - unless I try and access one of my public IP addresses from one of the private networks. In other words, my web server is My public ip of is mapped to that address. It works fine from the outside. On the inside, if I enter the public IP into a web browser on the internal network I get nothing. If DNS (on my ISP) is used to resolve a my domain to the public address, then it works fine from inside. A straight public IP just doesn't work from inside. Any thoughts?
Question by:digichip
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Accepted Solution

lrmoore earned 300 total points
ID: 8231392
This is a fairly common misconception of how NAT/routing work.
your internal clients can only access the internal IP address, not the public address.
You can setup your own DNS server, and you only need the one web servers IP address in it, with forwarders pointing to the ISP dns. This will let your internal users resolve www.yourcompany.com to the internal address, and the rest of the world resolves to the external public address.
Or, you can install a host file on every PC with the internal IP address of the web server. Try it on one system.

Author Comment

ID: 8231481
Thanks for your quick answer. I suspected something like that, but wasn't sure. I'm attempting to access a video file on my internal web server. The calling page is actually hosted externally on a Verizon server. I'm not sure why a direct IP request from an external web page should fail, but I assume it's because the page gets loaded onto my client (internally) before the request for the video file is made (using the external IP). At least now that I know it's not suppoed to work how I was trying to make it work I can focus on making it work some other way...


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