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The HTTP request 401.1 - Unauthorized: Logon Failed

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:

  1. Click Start, click Run, type regedit, and then click OK.
  2. In Registry Editor, locate and then click the following registry key:
  3. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
  4. Right-click Lsa, point to New and then click DWORD Value.
  5. Type DisableLoopbackCheck, and then press ENTER.
  6. Right-click DisableLoopbackCheck, and then click Modify.
  7. In the Value data box, type 1, and then click OK.
  8. 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

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