I have a business running Windows SBS 2011. The server provides AD, DNS, and Exchange services for the 15-computer company.
We recently have started experiences DNS errors for every client behind the firewall. Those on wifi (same cable modem) do just fine. The issue is intermittent, with about a 50-60% success rate for resolution. When DNS is not working, Simple Query's pass, but recursive query's fail.
Here are some items that might help understand the system:
TCP/IPv4 DNS is pointed to self at 10.1.1.2
Server has no port blocking of any kind on the firewall(only during troubleshooting)
Firewall is a Netgear Prosafe UTM5, updated.
DNS is using Root Hints only, no forwarders
DNS Round Robin is enabled
Firewall WAN port DNS address is set to Google DNS: 184.108.40.206, 220.127.116.11
Interfaces for IP has two IPv4 addresses and 3 IPv6 addresses enabled (perhaps I only need one of these?)
Any other questions, let me know.