I've just added a new DC on a remote site conncted through WAN. I also added a new site and put this DC inside . I also set the intersite replication policy. Everything seemed to work fine but in my head office my colleagues experienced the domain logon gets slower and generally AD lookup gets slower.
we have 2 DC in head office
1 DC in a remote site connected through WAN
For example if I try to set some authorizations on a Member Server in Head Office LAN, it gets 30 seconds to find the user name. Before adding the new DC it was instantaneous.