Do I need to setup separate User Profile Sync for each child domain?

Question

Our SharePoint 2013 on-premise farm is installed on our company major domain "Domain.com". We have setup user profile sync for domain.com. Under Domain.com there are several child domains a.com, b.com & c.com. These 3 domains have two-way trust with domain.com. On SharePoint users can locate a.com, b.com & c.com in people picker. However these 3 domain's user profile are not sync. Their "Display Name", "Email" and other attributes are not in User Profile database.

My question is, do I need to setup 3 additional UPS connection to these 3 domains? Or I should modify the existing connection (the connection for Domain.com)? Thanks.

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Follow up question: At the sync connection setup page, I have checked all domains as following picture:

If I click open the DOMAIN node > Users, I can see all users. If I click open A node > users. There is no user. Also, after I trigger a full sync, no user profiles from A & B domain are created.

In WFE server's DOS prompt I ran follow and get error:

C:>nltest.exe /dsgetdc:A Getting DC name failed: Status = 1355 0x54b ERROR_NO_SUCH_DOMAIN

I have verified with the domain controller admin A & B do have users. What could be the problem? Many thanks.

Answer 1

No, you should be using the single sync connection for the entire forest. If you have a secondary forest (or more) create a sync connection per forest.