Thursday, 28 April 2011

DisableLoopBackCheck : SharePoint 2010

I recently encountered an issue when I was working with one of my clients for providing them support on the deployment of master pages and updated solution files on their Standalone SharePoint 2010 installation.
Every attempt to log in into the local SharePoint 2010 environment by providing username and password failed and I was getting the username and password prompt continuously. As a result I was not able to access the site settings section of my SharePoint Server from  local server itself.
On a detailed investigation, It appeared that this issue has led to multiple issues in my SharePoint 2010 environment.

1)   Deployment Issues : The user will not be able to access the SharePoint Site Admin and hence will not be able to perform the deployment of master pages and layout page. The user will not be able to modify the settings available for the users.

2)   Search Administration :  if the SharePoint Environment hosts the Search Indexer also on the same SharePoint Box , then the indexer will be crawling itself and hence will not be able to access the content and the Crawl log  will be full of 401 error.

3)   Custom” scripts: Any custom script that is trying to access the web application while execution, the script will not be able to log in and hence will not be able to execute.

4)   Custom Code : Any custom code that requires to log in into the Web application will fail as it will not be able to log in when executed on the SharePoint 2010 Server.

This issue occurs because of a security feature added by Microsoft on Windows 2003 and Windows 2008 server.
you can either disable the loop back check entirely or else you can add a list of addresses to exclude them from the security check of the server.
To Disable the  Loop back check in the Registry, you need to perform any of the following:
  1. Go To Start—> Run –> Type Regedit, and then click OK.
  2. Locate the Following Registry Key :  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
  3. In Windows 2008, Add a new DWORD 32 bit, at the Lsa.
  4. Type “DisableLoopbackCheck” and then press ENTER.
  5. Right-Click DisableLoopbackCheck, and then click Modify.
  6. In the Value box, type 1 and then click OK.
You can also add the Registry entry,using the PowerShell :
New-ItemProperty –> HKLM:\System\CurrentControlSet\Control\Lsa –Name “DisableLoopbackCheck” –value “1”

Additional Details can be obtained from the following Microsoft Article

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