Howdy OS!
Generation of AD topology diagram is a "smart default" that needs to be enabled if you want that feature.
1. Go to Authoring -> Management Pack Objects -> Object Discoveries
2. Locate the "AD Topology Discovery" discovery that has Root Management Server as the target.
3. Select to Override the Object Discovery for specific objects of type: Root Management Server.
4. Change the override value to True and save the override.
Within a few minutes you should be able to see a diagram view at Monitoring -> Distributed Applications -> Active Directory Topology Root -> Open Diagram View.
/ John Joyner
/ MOM MVP
