The first domain controller in the first Active Directory forest will hold all five FSMO roles. All these roles are critical in the Active Directory infrastructure. Some of them are heavily used and some roles are only used on specific occasions. Some role owners will not be able to afford any downtime, and some role will still be able to have downtime. So, based on features, impact, and responsibilities, these can be placed on different domain controllers. However, FSMO roles placement is heavily dependent on characteristics of the infrastructure. Let's go ahead and look into few of those in detail.
FSMO role placement
Active Directory's logical and physical topology
If it's a single forest-single domain environment...
