Here is our current setup:
2 locations connected to each other via site to site vpn which is handled by a Zyxel USG50 on each end. Each location has 2 subnets in use. Each location has special applications that are used that are only accessible via a 10.96.x.x subnet because those are routed thru an ASA behind our Zyxel's at each location. Static routes are setup in our Zyxels to point to the ASA for those IP's:
Site A: Special Apps - 10.96.36.x Normal Domain - 192.168.100.x
Site B: Special Apps - 10.96.26.x Normal Domain - 192.168.200.x
Our SBS server is on the Normal domain subnet as it doesn't need access to the special applications so it's addressed: 192.168.100.15
The Site to Site VPN has all the rules so that all 4 subnets can communicate with each other. The problem we are experiencing is that all of the domain computers are constantly being kicked into "Working Offline" Mode and when this happens mapped drives are disconnected and you are unable to browse the internet, and Outlook loses it's connection to exchange. It seems like this is some weird DNS issue, but DNS isn't showing any errors on the SBS server. I also tried changing the script for mapping drives from \servername to \192.168.100.15 but the computers still get knocked offline.
Is it possible that the ASA's on both ends are interfering with DNS requests? All the domain computers that have been added have static IP's and have been set in the DNS tab to have a "domainname.local" DNS suffix as well as "register this computer in dns suffic" and "use this dns suffix".
Any help would be appreciated.