Some VPN servers / Bastard Operators From Hell configure the VPN session to disconnect forcing a re-signon entering username and password.
(In case you have wandered away from your laptop leaving their precious-most company lan at the tender mercies of the coffee shop waitress who just happens to also be an ueber-cracker)
Solution?
Open a terminal window.
Choose a deserving target
ping -i 30 target
This sends a packet every 30 seconds. VPN connection stays up!
Disable the virtual connection:
Control Panel -> Network and sharing -> left side open change adapter settings.
Right click on the virtual connection and select disable, and then enable your 'real' connection and see how this goes.
As per your comments, you are able to do this but after reboot, after a few minutes, the problem persist and connection is lost (although the V-ethernet remains disabled).
Since there is no difference between your "ping" of both your local router and 8.8.8.8 (eg ping 8.8.8.8) it confirms it is your machine.
Update
I would now open start, type in msconfig and in the start up menu, look for anything which is called vEthernet and disable it.
I would also open start, type in task s (to load task scheduler) and ensure there is nothing in here about the vEtherent.
Lastly, I would open start, type in services.msc and check here - it could be in there as a delayed start (this may be hard to find!)!
If there is no luck with the above, try a system restore.
Update 2
On the host computer, open Internet Options from the Control Panel. The Internet Properties dialog box opens.
In the Internet Properties dialog box, click the Connections tab.
On the Connections page, click the LAN settings button. The Local Area Network (LAN) Settings dialog box opens.
In the Local Area Network (LAN) Settings dialog box, deselect all the check boxes. Click OK twice to close both dialog boxes.
Restart the emulator and retry the connection.
Source
Best Answer
I deal with this sort of troubleshooting on a daily basis. The hard part about intermittent issues is determining where it is intermittent - you need the where before you can determine the why. The best way to start is to remove as many variables as possible. The best method is to start with your ISP device (t1 router, dsl modem, cable modem, etc) and connect it right up to the DMARC (smart jack if it is a t1, bonding device if it is eoc) using a new, short patch cable. Connect a laptop to the ISP device and run ping tests to your ISP's primary DNS (this is typically at your first hop and the best place to start). It it is only for a few seconds, set your ping intervals to 200 ms instead of 1 second and let it run overnight. If you see problems here, then it is your ISP's issue and you need to call them, they will do the rest.
Now if you see no issues here, then your problem is your IW or something on your network. Connect the ISP device back up to where you had it before and again, connect with just a laptop and run the same ping test again. If this is clear, then your IW is fine, and you know it is your network, if it is not clear, then run new cabling between there and the DMARC.
Troubleshooting your network is not something I'd be able to help with unless I had more information about it's setup, but the basics are to test the same way at each joint (typically routing point or switch) to see when the problem starts occurring again. This is not always easy, or successful, so sometimes tcpdump is required to watch traffic and see what is happening. This is not always easy and can be very time consuming, but may be your best bet.