Local LAN access to Public IP address

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Jul 16th, 2007
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I have have Cisco 877W router which has some web servers connected behind it. The Cisco has 8 static IP addresses on its dialer interface. Port forwarding is used to access the web servers from the internet using their designated IP adddresses.


However, from the local LAN I cannot use the public IP addresses of these servers to access them. Rather I have to use the local IPs.


This is causing a problem within the server configuration. if we use an external URL, eg x.x.x.x, to access the internet facing servers from the internal network, the address is inaccessible. Most of the time, this doesn?t present a problem, but there are times when it does. Specifically, we have to set a URL within the ?server? application to enable a particular communication process with the client PC. If we set this to the external address, external PCs can use this function, whereas internal PCs can?t, while if we set it to the internal address, external PCs then can?t use the function while internal PCs can. Therefore, is there anything that can be enabled on the router to allow the external IP address to be accessible from the internal network please?

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What you are looking to do is called 'Hairpinning' and is generally not allowed. I am fairly certain the 800 series will not allow it. It's basically the question, "why would you want to go out to stay in?"


An easy way around your problem is to use an internal DNS entry for the URL to internal IP or modify the Host file (assuming they are Windows boxes and you don't have an internal DNS serer) to do the translation for you.


The Host file is in WINDOWS\SYSTEM32\DRIVERS\ETC directory. If you modify the HOST file, you may need to do this not only on the web servers, but your internal clients as well.

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