JSI Tip 3654. Don't locate the Infrastructure Master and Global Catalog on the same server in a multi-domain forest?

Infrastructure FSMO Role

"When an object in one domain is referenced by another object in another domain, it represents the reference by the GUID, the SID (for references to security principals), and the DN of the object being referenced. The infrastructure FSMO role holder is the DC responsible for updating an object's SID and distinguished name in a cross-domain object reference.

NOTE: The infrastructure role should be held by a DC that is not a global catalog (GC). If this role is hosted on a GC server, cross-domain object references in that domain are not updated, and a warning to that effect is entered in that DC's event log."