I have a domain: DC, Internet gate and a couple of workstations. DC also works as DNS server. All queries to external names are being forwarded by the internal DNS server to the DNS server on Internet gate (actually, Kerio Control's DNS forwarder).
I found out that I can't resolve certain DNS names:
R:\>nslookup ru.secretvpn.net
Server: dc.mydomain.local
Address: 192.168.0.1
*** dc.mydomain.local can't find ru.secretvpn.net: Server failed
Other names can be resolved just fine (including secretvpn.net itself). If I specify DNS server (the one from the settings of the WAN NIC on Internet gate) resolving also works fine. It also works on Internet gate itself.
So the issue is bound somehow with DNS queries forwarding from the internal DNS server to the DNS forwarder.