Re: DIrSync - Multi-Domain Forest

Hi Mike,

I think I may not expressed myself clear before.

DirSync is AD-based synchronization with Office 365 and communicates with your domain controller servers instead of the child domain. Also it needs to meet the following requirements:

1. It must run on a Windows Server as operating system.
2. It must be joined to Active Directory.
3. It cannot be a domain controller.
4. It must run Microsoft .NET Framework 3.x which already has been installed in Windows Server 2008 or higher.

I suggest you refer to the videos in Office 365: Configuring DirSync and Single Sign On with ADFS to go through the process of how to deploy DirSync, then check if there are any misconfigurations when deploying DirSync. 

For more details, please refer to: Prepare for directory synchronization.