The Active Directory has 5 FSMO roles which are dedicated for certain tasks in a domain enviroment which should not be performed by all domain controller. The role Infratructure Master has cause a bit of confusion ever since it appeared in Active Directory in Windows 2000 so here’s a quick explanation of it.
The Infrastructure Master is a domain-wide role (which means one in every domain and not one pr forest) and is used in a multiple domain forest to track and check all references to resources, such as user account, in the other domains. These references are knows as “phatom records” and are used by domain controller who are not Global Catalogs(GC). I’ve heard statements that infrastructure master can’t reside on a GC but that’s not exactly true, the infrastructure master can reside on any domain controller. However it will not function properly unless it resides on a non-GC DC in a multiple-domain forest.
- If your forest has only1 domain: Infrastructure Master is unemployed and you are free to place it anywhere
- If all DCs in your forest are also GCs: Infrastructure Master is unemployed and you are free to place it anywhere
- If your forest has at least 2 domains AND not all of your DCs are GCs: Place the infrastructure master on a non-GC DC.
Also notice that when upgrading your domain to 2008 R2, you must (as part of the preparation) run adprep /domainprep command on the server hosting the infrastructure master role.