We are having some strange DNS issues. We have a main site with multiple remote locations. The main site is connected to each location via a site-to-site VPN. Each Sonicwall TZ210 manages the DHCP for their site. At the main site, we have a couple Domain Controllers, two of which are used for DNS. The Sonicwall VPN's have two the two servers from the main site, and a third DNS through the ISP.
The problem is that a handful of people at remote sites experience connectivity issues to the mapped drives. It used to be that you could access teh servers through the IP address, but this changed suddenly. You cannot ping/run NSlookup. NSlookup cannot find hte name, and times out after 2 seconds. We cannot figure out why this is happening. We are using a Server 2008 box with FSMO roles, and have a 2012 DC, and other 2008 DC's as well. We do not use IPv6, and it is not enabled on the servers.