Does the Primary Domain Controller have to be visible to all other DC's at all times?

Hi

I am deploying a second 2012 Server in a remote office and would like to know whether the Primary DC (also Server 2012) in the head office needs to be visible to the remote office at all times?

I will be joining the new server to the domain via VPN but would then like users to log into the new DC regardless of the VPN being active or not. The VPN should be up 95% of the time.

If this is possible, is there a certain way that the new DC needs to be set up that is different from a standard install and promote to DC?

Thanks in advance