If you want to share address lists between multiple forests (cross-forest sync) different topologies are to be considered. Using GALsync in a mesh-topology provides a synchronizing of Global Address List between each Exchange organization, in a uni-directional 2-way sync only data between a source and a target organization would be exchanged. In this blog we describe the basics of different topologies realizing a synchronization model as you need.
A simple uni-directional continous export of GAL in a 2 forest environment
Assumed that you want to share addresses from forest A to forest B, you have to install GALsync in the appropriate domain of forest A and select the objects you want to replicate to forest B.
If you want to receive the addresses from forest A in forest B, you have to install GALsync in the appropriate domain of forest B, create a new Organizational Unit and place the new objects in this OU. The new objects are created as mail-enabled contacts referring in their “targetaddress” attribut to the original object in forest A. There will be no mailbox in forest B for this object!
Result: If somebody in forest B performs a Gloabl Address List lookup in Outlook and he selects one of the imported objects this mail is forwarded directly to the recipient in forest A.
A simple bi-directional continous synchronization of GAL between 2 forests
A synchronization of GAL between 2 forests consists of two uni-directional replication steps. Each forest exports it’s data to and imports the data from the other site. Every site makes it’s own decisio which data should be available for it’s partner site.
Synchronize GAL in a multi-forest environment
Often a multi-forest environment is present after company take-overs without a strong need of migration into one forest. Trusts are not required in organizations with multiple Active Directories if you only want to share Global Address List (GAL). GALsync offers a simple Inter-Org Sync without trusts.
In a Star-Sync topology the headquarter’s forest would receive all data from the affiliates forests.
The affiliates forest are not able to share GALs directly but receive all required data from headquarter forest.
In a Mesh-Sync topology everybody shares his data with everybody. So each forest is independent to decide who is getting what data. This allows a full replication of information between multiple independent Exchange organizations.
From GALsync’s point of view it doesn’t matter which topology you use to synchronize objects between multiple Exchange organizations. It’s more a question of administration. In a Star-Sync topology the affiliates only need to configure 2 policies: one export and one import policy. Only the headquarter requires an import poliy for each affiliate as well as a export policy to every affiliate.
In a Mesh-Sync erverybody requires as much policies as bi-directional syncs he wants to perform.
From an administrative perspective you might organize data in different organizational units if they are imported from different sites.