Symptoms
When you use the fully qualified domain name (FQDN) or a custom host header to browse a local Web site that is hosted on a computer that is running Microsoft Internet Information Services (IIS) 5.1 or a later version, you may receive an error message that resembles the following:
HTTP 401.1 - Unauthorized: Logon Failed
Cause
The security feature loopback check prevents access to a web application using a fully qualified domain name (FQDN) if an attempt to access it takes place from a machine that hosts that application.
Workaround
You need to disable the loopback check by setting the DisableLoopbackCheck registry key.
To set the DisableLoopbackCheck registry key, follow these steps:
- Click Start, click Run, type regedit, and then click OK.
- In Registry Editor, locate and then click the following registry key:
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
- Right-click Lsa, point to New and then click DWORD Value.
- Type DisableLoopbackCheck, and then press ENTER.
- Right-click DisableLoopbackCheck, and then click Modify.
- In the Value data box, type 1, and then click OK.
- Close Registry Editor, and then restart your computer.
The easiest way to add this parameter to the registry - run cmd and paste the following command:
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa" /v DisableLoopbackCheck /t REG_DWORD /d 1 /f
Reference