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I am running a Windows Server 2008 R2 with 3 nics (2 with external IPs, 1 with internal IP). The two external IPs are associated with two web sites running on that server. The third nic is for communication with a backend server. Everything is working fine, both website are reachable from outside. Now I need my backend server to make a connection to the outside world. To do this I activated and configured NAT on my described web server.

Now the Problem: when activating NAT, one of the external IP adresses becomes unreachable. Deactivating NAT makes the second external IP again reachable. Tatally repoducable!

What shoud I do? I need both external IPs and the NAT Function! Can somebody help me out??

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How did you configured NAT?

Did you use Routing and Remote Access?

For NAT to work correctly, you have to configure it in Routing and Remote Access - every interface must be added and set up correctly in NAT settings. In addition, if any interface is configured to be public and you want to access server through that interface, you have to explicitly allow communication on desired ports for that interface.

More information about configuring NAT with Routing and Remote Access on Microsoft website:

Enable and Configure NAT

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