Topic Last Modified: 2010-06-23

Site Link Transitivity works together with the W2K3_BRIDGES_REQUIRED option to let an Exchange administrator provide access to public folders in remote sites. By using this method, you can avoid the potential overhead of generating replication over a large Active Directory directory service topology.

You may have a large Active Directory site topology that is made up of many sites. Additionally, you may have users from one site who must access public folders when they log on from another site. Consider the following scenario:

• You have several hub sites that are connected to one another by using high-speed network connections. For example, Site A, Site B, and Site C are interconnected.
  
  
• You have many other sites that are connected to only one of the hub sites over a slower connection. You do not have a mesh topology in which all the sites are interconnected. For example, Site 1 and Site 2 are connected only to Site A, Site 3 and Site 4 are connected only to Site B, and so on.
  
  
• Typically, users in a particular remote site access public folders from that site.
  
  
• Occasionally, users from a remote site (for example, Site 1) require access to their public folders when they are in another remote site (for example, Site 3).
  
  

In this scenario, you have the following options:

• Public folder replicas: You can configure public folder replication over the WAN links. This option is best suited in an environment in which the WAN usage for public folder access exceeds the cost to replicate the public folders over the WAN. If users require only occasional access to the public folders, replicating the public folder content will likely cost more than WAN access of the public folder content.
  
  
• Public folder referrals: You can use public folder referrals in an environment in which the public folder replication cost exceeds that of public folder access over the WAN. The following basic methods can configure public folder referrals:
  
  
  • Reactive: This configuration method waits for a user request to the public folder content before access is granted to the public folder. This method costs less in support costs, but has more user dissatisfaction.
    
    
  • Proactive: This configuration method creates a large matrix of public folder referrals. This method has a small effect on users. However, depending on the number of sites, this method might have a large effect on support costs. For example, in a multi-site topology that contains 300 sites, you might have to create up to 90,000 Exchange referrals (300 x 300).
    
    
• Active Directory site transitivity: This method lets you configure site transitivity together with the W2K3_BRIDGES_REQUIRED option to control Active Directory replication with domain controllers that are located in adjacent sites. This option may provide you the greatest flexibility and provide a balance between user access and WAN cost in a large multi-site organization.
  
  

Active Directory site link transitivity together with the W2K3_BRIDGES_REQUIRED option is fully supported for use in an Exchange 2007 organization. This feature lets you constrain the KCC to adjacent site links as you keep topology-wide cost determination by using intersite messaging. Active Directory site link transitivity is available in a Windows Server 2003 or higher version forest-functional level. For more information about how to configure this feature, see the "Bridging Site Links Manually" section in How Active Directory Replication Topology Works.

For More Information

To ensure that you are reading the most up-to-date information and to find additional Exchange Server 2007 documentation, visit the Exchange Server TechCenter.

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