basically we have 2 DC servers which used to have site-2-site VPN but it's not working anymore. So we started to get various errors, DNS stopped working, etc, etc. As a last resort attempt (before manually demoting one of the DCs), i want to "connect" them via public IP - so I can, at least, do a clean demote. But I can't figure out what I need to do for this. Both servers have 2 NICs, one with internal and one with external IP.
how should I point one DC to replicate with another one over public IP?
DC's use DNS.
Now, you hook up both sides with the public IP, THen go into the DNS on both sides and start working through all relevant entries so that the IP-Addresses match up. Right now they do not see each other and think that the other side is on another IP, which makes any sync hard.
Not sure which entries you will need to fix up for things to start working again - "all relevant". May be as simple as the IN A entries for the names on both sides, so they can ping each other.