To support a resource forest topology, Lync Server 2010 must be deployed in your resource forest and configured at minimum with one-way trust between the resource forest and all user forests (such that the resource forest trusts all user forests).

Warning:
You must establish a two-way trust between the resource forest and user forests to enable distribution group expansion when groups from user forests are synchronized as contacts to the resource forest. Two-way trust is required between the Microsoft Exchange Server and Lync Server forests, if they are deployed in separate forests, for enabling Exchange Unified Messaging (UM).

The following shows how an example organization, Contoso, configured a Front End pool in its resource forest.

After you have deployed Lync Server in the resource forest, complete the following steps:

• Create disabled accounts with the corresponding attributes for each user account in the user forests. This process will vary depending on whether or not you have Microsoft Exchange Server deployed in the resource forest where Lync Server is installed.
  
  
• Enable the disabled accounts you created for Lync Server.