DFS gurus might recall that DFS site costing functionality can be negatively impacted when the Bridge all site links option is disabled in Active Directory. Fortunately this has changed for Windows Server 2003 SP1. Details are provided in the How Active Directory Replication Topology Works Technical Reference; I’ve included the relevant text below. We’ll work on getting the DFS documentation updated with this information.
When the forest functional level is Windows Server 2003 or Windows Server 2003 interim and the ISTG does not use Intersite Messaging to calculate the intersite cost matrix, DFS can still use Intersite Messaging to compute the cost matrix for its site-costing functionality, provided that the Bridge all site links option is not turned off. In branch office deployments, where the large number of sites and site links makes automatic site link bridging too costly in terms of the replication connections that are generated, the Bridge all site links option is usually turned off on the IP container (CN=IP,CN=Inter-Site Transports,CN=Sites,CN=Configuration,DC=ForestRootDomain). In this case, DFS is unable to use Intersite Messaging to calculate site costs.
When the forest functional level is Windows Server 2003 or Windows Server 2003 interim and the ISTG in a site is running Windows Server 2003 with SP1, you can use a site option to turn off automatic site link bridging for KCC operation without hampering the ability of DFS to use Intersite Messaging to calculate the cost matrix. This site option is set by running the command repadmin /siteoptions W2K3_BRIDGES_REQUIRED. This option is applied to the NTDS Site Settings object (CN=NTDS Site Settings,CN=SiteName,CN=Sites,CN=Configuration,DC=ForestRootDomain). When this method is used to disable automatic site link bridging (as opposed to turning off Bridge all site links), default Intersite Messaging options enable the site-costing calculation to occur for DFS.