3.1.5.5.1.2 DomainServerRoleInformation

If the server is not a domain controller (DC), the Buffer.Role.DomainServerRole field MUST be set to DomainServerRolePrimary.

If the server is a DC and the fsmoRoleOwner attribute value of the account domain object is equal to the distinguishedName attribute value of the server's computer object, the Buffer.Role.DomainServerRole field MUST be set to DomainServerRolePrimary.

Otherwise, the Buffer.Role.DomainServerRole field MUST be set to DomainServerRoleBackup.