IIS site not responding from some machines, DNS correct

Question

This is a strange one. I have a site set up on IIS 6, this site has a unique IP assigned to it. The strange thing is that it works from some locations and it just doesn't from other locations. DNS is resolving to the right IP address, however pinging to that address times out. Any ideas why the site doesn't work?

As a note, I have other sites running from the same VPS, but using a different IP address. and they are working fine.

Cheers

Answer 1

Since it's not pinging, it's at a lower level than IIS. My only guess is that you have some custom firewall rules in place. Also confirm that your server does listen to pings, just so that you know for sure what the expected response should be.

To troubleshoot, narrow this down to the smallest part. i.e. ping the IP of a good site and failed site and confirm that one listens to the IP and the other doesn't. Try the same from a computer where both sites work.

Consider any patterns in the computers where it doesn't work from. Are they in a different subnet, in a different part of the Internet? Review all firewall rules in the path from the failed computers to the server.

Answer 2

Try tracert from both directions. Are they following the same route? Maybe the response from your server is going on a different route that is blocked.

Answer 3

It sounds like you might be running into an issue with Socket Pooling. From Microsoft's technical whitepapers:

In IIS4, you could bind different Web sites to different IP addresses. Sites did not share sockets, but each site on a unique IP address had several sockets. These sockets are created when the site starts, and they consume significant non-paged memory (RAM). This memory consumption limits the number of sites bound to IP addresses that can be created on a single machine.

For IIS 5.0, this process has been modified so that sites bound to different IP addresses, but sharing the same port number, share the same set of sockets.

Socket Pooling continues from IIS 5.0 to the current Windows versions. Try disabling the socket pooling and see if you can get your web site working. I ran into this problem and wrote a blog post about it titled Separating IP:PORT Bindings on Windows.