Consider the following scenario:
You set up a Microsoft Forefront Threat Management Gateway (TMG) 2010 array that has multiple domain member nodes.
You enable the EnableSharedCookie option to allow for external authenticated users to be handled by all TMG nodes.
You configure the TMG firewall service to run as a specific domain account so that internal clients can use the Kerberos protocol to authenticate with the TMG nodes.
In this scenario, you find that external users are prompted unexpectedly for authentication when they are redirected between TMG nodes.
This problem occurs because Forefront Threat Management Gateway does not use the Domain account for the remote procedure call (RPC) that's used between nodes to exchange user credentials.
To resolve this problem, install Rollup 5 for Forefront Threat Management Gateway (TMG) 2010 Service Pack 2.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.