I installed a VPN client (FortiClient) few days ago. Every VPN client installs a new adapter which you can see from Network Connections in Control Panel. (Network and Sharing Center -> Change Adapter Settings). After you connect the VPN, the problem begins when you try to browse web using browser. Every website you try to visit takes much longer time to load than before when VPN is disconnected. I know it does not occur in all machines (also not in my Windows 7 PC) but it occurred in my Windows 8 Release Preview OS.

The problem lies in the order of DNS servers. As soon as I connected to VPN, the default DNS server is overwritten by VPN DNS like 192.168.19.11. So, every request for any domain has to go through that DNS server (192.168.19.11) before regular DNS server. When I did nslookup on google.com, it goes to 192.168.18.11 and gives timed out error as shown below. That was causing delay in browsing web sites.

DNS lookup timed out.

So, I tried to reorder TCPIP Linkage binding order from registry as suggested in this article. 

But, it is soon reversed back if I disconnect and reconnect VPN. In other words, VPN DNS server becomes primary. It seems bug in Windows OS. At the end I had to come up with not-so-perfect work around. I manually edited DNS Server address for VPN Connection pointing it to correct one. It turned out to be perfect solution as browsing web sites and remote desktop connection from VPN tunnel also worked normally.

You can view DNS Server address by running “ipconfig /all” in command prompt.

Manual overwriting of DNS Server address

Successful DNS Lookup