I was debating what section to actually post this...
I have users making VPN connections through a Cisco PIX and authenticating via RADIUS to a Windows 2000 server running IAS and RRAS. My Mac OS X and Linux users, once connected are able to resolve addresses to their internal IP through our internal name server running BIND. However, Windows XP users when trying to resolve internal names in DNS recieve external IPs as if they were using another public DNS server.
In Windows XP, while connected through VPN, I can run ipconfig /all and see that the correct DNS Server is in place. However, when doing an nslookup, it's trying to use the local router of where the computer is VPN'ing from as the DNS server. For example, I'm connected to my office VPN from home and when I run nslookup it is using my home router's IP as the default server. I've also tried doing an ipconfig /flushdns to no avail.
As I said, it's just on Windows where I have this problem and it's multiple if not all Windows VPN users. We have another main office that has pretty much an identical setup as mine except they use Microsoft DNS and when making a VPN connection to their network I have the same problem.