You configure Microsoft Forefront Unified Access Gateway 2010 to use the Use local Active Directory forest authentication option. In this case, Forefront Unified Access Gateway detects and uses only a single global catalog server in the forest to query for existing domain controllers during trunk authentication.
If this global catalog server is offline or otherwise unavailable, Forefront Unified Access Gateway will not detect this condition and becomes unable to locate domain resources for authentication. Trunk authentication by using this local Active Directory forest authentication repository option continues to fail until the server is restarted, and a different global catalog server is detected.
This problem occurs because, in order to perform Active Directory Domain Services (AD DS) forest authentication, Microsoft Forefront UAG User Manager (the UserMgrCom service) performs a Domain Name System (DNS) query for the Active Directory _gc srv records. The UserMgrCom service does this to find an available global catalog server, based on the authentication repository forest configuration. After a global catalog server is selected, and the connection information is cached, the UserMgrCom service does not perform any additional query or create a new global catalog server connection until the service is restarted.
To resolve this problem, install Service Pack 4 for Microsoft Forefront Unified Access Gateway 2010.
To work around this problem, manually restart the UAG User Manager (the UserMgrCom service) to start a new global catalog server query and connection if the original global catalog server is no longer available.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
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