The question [1] tells: "In Windows 2008, we find that TCP connections from public ip e.g. 1.2.3.4 to 127.0.0.1:8334 fail" MS KB article [2] (on Loopback Check security feature in Windows-es) explains this as: "authentication fails if the FQDN or the custom host header that you use does not match the local computer name" QUESTIONs (reformulating [4]): 1) Aren't FQDNs of of both 127.0.0.1 and 1.2.3.4 (of the same machine) from the question [1] the same? 2) Don't FQDN of 1.2.3.4 match local computer name (in case of TCP connection from 1.2.3.4 to 127.0.0.1) in question [1]? 3) I'd be grateful if you answer questions [3] related to these questions Cited: [1] The question "Windows Server 2008 - Connecting to 127.0.0.1" http://serverfault.com/questions/170476/windows-server-2008-connecting-to-127-0-0-1/ [2] You receive error 401.1 when you browse a Web site that uses Integrated Authentication and is hosted on IIS 5.1 or a later version http://support.microsoft.com/kb/896861 [3] The question "On disabling Loopback check security feature in Windows XP Pro SP3" http://superuser.com/questions/178187/on-disabling-loopback-check-security-feature-in-windows-xp-pro-sp3 [4] What are FQDN of my localhost, 127.0.0.1, APIPA and DHCP attributed ip? http://social.technet.microsoft.com/Forums/en-US/winserversecurity/thread/a03ab9b9-e550-463c-b060-5776078d4064