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Will they be resolved by my VPN provider, or by my original ISP (if left on "automatic" settings)? Would I have to manually configure a dns server, to make sure my requests will not be resolved by my ISP (constituting a privacy risk)?

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The requests will be passed to the IP that's configured. So if your DNS is still your ISP's DNS, then yes you will still be asking your ISP to resolve a domain name for you.

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Windows Vista has an "automatic" setting, the default setting for finding a domain name server (no ip is explicitly set with this setting). If left on automatic, do you think this would mean any dns requests go to my ISP? – Samuel Apr 18 '12 at 8:55
I would just set an explicit IP, I don't know what would happen if you use the automatic setting. It might be you do get a new DNS configuration if the VPN provider sends you one when you request an IP. Just test it I guess :) – Lucas Kauffman Apr 18 '12 at 9:01
Ok, that makes sense. Thanks! – Samuel Apr 18 '12 at 9:06
@Samuel Yes. If you have a standard set up: Router using DHCP then 'automatic' will obtain a DNS server over DHCP which will point to your local router, your local router will then use your ISPs DNS servers for DNS lookups. – Andy Smith Apr 18 '12 at 9:07
What if the VPN tunnel is a virtual interface with it's own DNS configuration? How would the Windows OS's choose DNS server? For Linux, I assume the /etc/resolv.conf will be updated with the newest interface... – Dog eat cat world Apr 20 '12 at 14:40
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Depending on how your VPN is configured, you might or might not use the same DNS for your VPN and for Internet. VPN's are (typically) like an additional IP stack on your system, and can have a separate DNS server address configured. But not all systems do this.

  1. If your VPN does not assign a new DNS for the VPN session then you will continue to use the DNS server(s) configured in your main Internet IP Stack. This can present a problem if the external DNS cannot resolve internal addresses (or as you indicate, if you don't want internal addresses to be known externally).
  2. If your VPN does assign a new DNS - for example by using DHCP option 6 "DNS Server" - then you can have different DNS servers for the VPN and for Internet. Your OS must support this, as must the VPN service. If you send traffic out both stacks at once this would be "Split Mode".
  3. A final option is that you might operate your VPN in Tunnel Mode, sending all communications (including Internet) through the VPN stack. In this case, when you are on the VPN all DNS would use the VPN's DNS. This is probably the most secure way since all internal traffic is sure to stay in the VPN.
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Excellent answer, covered all the options here. One other thing to note is that how it is configured can also depend on which VPN you're using - not all vendors' products support all the options. – AviD♦ Apr 18 '12 at 22:20
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Depends on how your 0.0.0.0 route is setup after making a vpn connection. If it goes through your vpn GW, then it won't matter what ip you use, but how its getting there.

You can always define persistant routes to get your local GW to egress for your dns requests.

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