Enabling the Bridge All Site Links Option

Applies To: Windows Server 2008

Site link transitivity is controlled by the Bridge all site links option on the properties pages of transport folders (such as IP or SMTP) in the Active Directory Sites and Services snap-in. Site link transitivity is enabled by default.

If you leave the Bridge all site links option enabled, you have to create a site link or add the site to an existing link only when you add a new site or remove a site so that least-cost replication paths are created automatically. The Knowledge Consistency Checker (KCC) on a read-only domain controller (RODC) always creates an inbound replication connection from a writeable Windows Server 2008 domain controller even if the KCC has to traverse many site links to establish the required replication path.

In addition, Distributed File System (DFS) can compute the cost matrix for its site-costing functionality. In other words, if you disable site link bridging and you are using File Replication Service (FRS) to replicate DFS replicas, which include the SYSVOL share, the DFS site-costing ability is also disabled.

However, with the Bridge all site links option enabled, domain controllers run the Intersite Messaging service periodically to build a spanning tree graph with the costs of the various branches of the topology. If you enable the Bridge all site links option in a large environment that has approximately 1,000 sites or more, the Intersite Messaging service can cause a spike in CPU use by the Lsass.exe process on domain controllers when the KCC runs. By default, the KCC runs every 15 minutes.

If you want to leave the Bridge all site links option enabled for applications that can take advantage of site link bridging, such as DFS, and you want the KCC to ignore the Bridge all site links setting for performance purposes so that the KCC uses only published site links and manual site link bridges, run the command repadmin /siteoptions +W2K3_BRIDGES_REQUIRED in the sites where you are concerned about KCC performance impact. To run the command, you must know the name of a domain controller in the site.

The command syntax is as follows:

repadmin /siteoptions <domain controller> /site:<site name> +W2K3_BRIDGES_REQUIRED

For example, to run the command on a site named Branch01 that has a domain controller named DC01, type the following command at an elevated command prompt, and then press ENTER:

repadmin /siteoptions DC01 /site:Branch01 +W2K3_BRIDGES_REQUIRED

Some applications and features that can take advantage of site link bridging include the following:

  • DFS

  • Microsoft Exchange Server 2007

  • The TryNextClosestSite setting for DC Locator

  • Automatic site coverage

  • Universal and global group membership caching