If your D-Link router disconnects every 4 minutes when you connect to your office network (VPN) from home:
In D-Link manager (from laptop wired to it), at top choose "Advanced," then on left "Application Rules."
Create a new rule specifically opening the port used by the network:
Check the top left box. In the "Ports" column, type "1723" in the blanks labeled "Trigger" and "Firewall."
Click "Save Settings," then "Reboot."
(If not fixed, ask your network administrator for the number of the network's open port. Try that instead of "1723," which is the Microsoft default.)
You can confirm that it is open by connecting to your network, then going to YouGetSignal.com:
Choose "Port Forwarding Tester."
It should show the IP address for your network.
Type in the blank for "Port Number" "1723". Click the "Check" button. It's working if it responds that that port "is open."
To see how long before it disconnects:
Connect to your office network. Click the icon for that network on the Windows toolbar at the bottom of your desktop.
[Mine: D-Link DIR-628 wireless router.]
D-Link support level 3 told me this recipe after I spent about 3 working days talking to levels 1, 2, and 3, including replacing my router....
Last night they promised to update this forum and educate their phone people....
I have no idea why D-Link software doesn't automatically keep that port open....