Ever since upgrading to Snow Leopard, I find that my DNS lookups go pear-shaped after 2 minutes or so. To be precise, I stop being able to resolve names that are only resolved by the specific servers delivered by the PPTP server, as opposed to the ISP's hosts. Apparently, something is overwriting the servers from the PPTP server with other hosts. Anybody got a way around this?
Snow Leopard seems to have broken DNS settings from VPN connections. It worked fine in Leopard.
As a band-aid, I put two scripts in /etc/ppp: ip-up and ip-down. I use them to save the current DNS, change it to the VPN dns, and when disconnecting, change it back.
It's ugly but works.
/usr/sbin/networksetup -setdnsservers "Interface Name" [ip of dns server]
This sounds more like your VPN itself is dropping than a DNS problem. If you ping the IP that you are VPNing to are there any lost packets?
After DNS breaks can you connect to something at the VPN site by local IP instead of by DNS name?
Do you have a manually entered DNS entry or is it delivered via DHCP on both your local network and the VPN network?