I have two domain controllers for the same domain, in two sites. The sites are now going to be separated by a firewall. What ports need to be open between the two DCS on the firewall so that AD continues to replicate happily?
You need to open more than one port, I think it’s about 15 of them.
There’s actually a couple of different ways to get AD to replicate through a firewall. Microsoft has a little article about it that may help.