I have 3 AD servers with windows server 2008 R2 at 3 different places, main server is at datacenter and 2 are in our local office which are at 2 different place.

I want to synchornize all the 3 server together, were datacenter server should be central server and rest 2 servers should synch with the datacenter server. Please provide us the steps or tutorial to do this.

Also we want that once the changes are done in 1 of the AD server the changes are automatically done in all the servers. For example if I change the password of user in our local server it should be updated in our main AD server and other branch server too.

Please provide us the steps or tutorial to do this asap.

I have one more question I have already created main datacenter AD as domain.local and other domains as xyz.local and abc.local, how can I replicate the additional AD domains with main datacenter DC, also do we require VPN connection, is there any other way to replicate the servers without using VPN connection?