DNS may acquire correct address during nslookup but does not resolve correct with ping or any services. It continues to default to LAN DNS. Adjust the ethernet or wifi weighing so that Windows 10 uses VPN DNS first.
correct, common problem:
http://answers.microsoft.com/en-us/windows/forum/windows_10-networking/win-10-dns-resolution-of-remote-network-via-vpn/513bdeea-0d18-462e-9ec3-a41129eec736
Source
Changing the metric worked for me, but my situation was a little different:
DNS resolution with my VPN had been working flawlessly with Win10 (first with Preview, then with RTM, always kept up-to-date) using Dell SonicWALL NetExtender (currently version 7.5.223)
Then this morning DNS resolution with my VPN stopped working suddenly. I hadn't explicitly made any changes or installed any updates or software. Perhaps an automatic update broke things.
Though the VPN still connected fine, and though the interface binding order HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\LanmanServer\Linkage\Bind was properly updated on connection of the VPN (i.e. the VPN's interface was added to the top of the list), NSLOOKUP would use my LAN's DNS servers rather than the VPN's DNS servers. The VPN client was however showing properly-configured DNS servers.
In my case I was unable to open TCP/IPv4 properties for the "SonicWALL NetExtender" interface: the "Properties" button was displayed as being active, but clicking on it did nothing / did not open a properties dialog.
So instead I went to TCP/IPv4 properties for my Ethernet interface, clicked Advanced, and unchecked "Automatic metric", and assigned an arbitrary metric of 100.
After doing this DNS resolution once again works properly: When the VPN is connected the VPN interface's DNS servers are used. When the VPN is not connected, the Ethernet interface's DNS servers are used.