Q:

Active Directory not replicating

I have a windows server 2003 as a PDC ("server 1"). I am attempting to take it offline once I get several issues cleared up. I have two other windows server 2008 servers that have been promoted as DC's ("server 2" and "server 3"). 
When I run dcdiag on any of the servers I get failed connectivity to "server 2" and "server 3" 
the host guid._msdcs.domain could not be resolved to 
an ip address...although the guid dns name couldnt 
be resolved, the server name resolved to the ip address. 
Check that the ip address is registered correctly with 
the dns server. "server 2" failed test connectivity. 

While there could be several issues preventing replication, I noticed one thing on the pdc ("server 1"). In DNS under the msdcs folder there is an "" folder (along with "dc", "domains", "gc" and "pdc". The "_" folder references "server 2" with the guid thats referenced in the dcdiag connectivity failure. 
What does the "_" folder represent? Is that where my problems begin? The pdc has the wrong guid for "Server 2". I need to be able to replicate to "server 2" and "server 3"

A:

Answers to your questions re: the DNS records are certainly something you should know about (and I'd encourage you to look at something like this article from Microsoft for some background on what they do), but I think you're probably interested in a more practical answer here.
What are the "server 2" and "server 3" computers using for DNS servers? I'm guessing that your "server 1" computer is a DNS server (since it's your existing Domain Controller), but it's unclear if you've configured "server 2" and "server 3" to be DNS servers.
I'd configure both "server 2" and "server 3" to be DNS servers, with "server 1" specified as their sole DNS server initially. Once Active Directory replication is working as-expected I'd reconfigure "server 2" to use "server 3" as its primary DNS server and itself as its secondary, and the converse on "server 3". Then you can go about transferring the Floating/Flexible Single-Master Operations (FSMO) roles from the "server 1" computer to either of these new machines, and demote "server 1" to a member server for removal from the network.

