On a new server, I ran into a problem where IIS was not showing any of the IP addresses bound to the primary NIC.

Furthermore, instead of the expected IP addresses, there was a mystery IP that began with a zero, which was not listed in any of the network interfaces, and which did not show up in the output of ipconfig.

Googling for the problem only turned up Microsoft KB2551090, but it didn’t seem to apply, since we do not use the “skipassource” flag.

A registry search for the mystery IP address yielded no results. Where did the IP address come from?

Out of desperation, I tried a “geolocation” IP address lookup to see if that would give me a hint, but it turns out that IP addresses beginning with a zero are not valid.

But I DID happen to notice that the IP address, when converted to a decimal number, was exactly the same as the computer name, which consisted only of numbers. This was a machine that we did not set up, so we didn’t choose this particular name.

On a hunch, I figured that IIS didn’t like the numeric computer name. I renamed the machine to have letters, rebooted, and violá: The expected IPs were in IIS.