The HOSTS file on my server has the standard entry 127.0.0.1 mapped to localhost. I can ping localhost, and I can access the Default Web Site when I enter http://localhost. However, when I enter http://127.0.0.1, I receive a Page not found error. Why isn't IIS responding to the IP address?

IIS might not be responding for a couple of reasons. First, be certain that you've configured the Default Web Site to respond to 127.0.0.1 by entering that IP address specifically in the Default Web Site's Properties dialog box. You might also want to enter other IP addresses that you'll use to access the site. Alternatively, you can set the IP address to All unassigned, although I don't recommend using that setting because you never know what someone might do in the future to IP addresses that go to that server.

Second, Microsoft Internet Explorer (IE) might be causing problems by routing your 127.0.0.1 request to any proxy server you've set up. By default, IE treats any address that contains a period (.) as an Internet address. Thus, localhost is routed locally, but 127.0.0.1 is sent to the proxy server. In IE, select Tools, Internet Options, then click the Connections tab. Click LAN Settings. If the Use a proxy server check box is selected, select the Bypass proxy server for local addresses check box, too.