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
- 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).
- 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.
- 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
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.
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