Cannot get the sysvol folders to replicate between Domain Controllers

I have 2 domain controllers communicating thru a Cisco site to site VPN tunnel.  One domain controller is on a network and the other is on a network. I have checked with Cisco and the VPN tunnel is working correctly.  I have DFS set up on both domain controllers and that seems to work fine.  I can also add and remove users from both domain controllers with no problem.  The problem I am having is the sysvol folders are not replicating.  I get errors when I run dcdiag and dcdiag /fix or netdiag /fix.  The error I get with dcdiag is:  

"Warning could not confirm the identity of this serverin the directory versus the name returned by the DNS servers.  If there are problems accessing this directory server then you may need to check that this server is correctly registered with DNS [servername] Directory binding error 5".  

I have registered the DNS server, I can ping both servers with no problem using "servername" and "servername.DNSsuffix" I checked the sysvol shares and they seem to have the correct permissions on them.  The sysvol has never replicated from the beginning.  
Any help would be appreciated.
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ChiefITConnect With a Mentor Commented:
DFS is responsible for sharing Sysvol. It uses netbios broadcasts to do this. Netbios is a not routable protocol. So, you have to use WINS between your two lead site servers in order for DFS to share between them.

Non-routeable is defined as going over NAT, through a firewall or over a VPN tunnel.

Below is a picture of what it should look like and to confirm that DFS uses netbios please look at the following link:

This pic explains how to set up the master browser service for a VPN. It too uses netbios broadcasts.
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