OpenVPN and LAN/WLAN Switching


Automatic LAN/WLAN Switching is a relatively good idea. On a notebook, it prevents you from remaining on the wireless network when you have already connected to the LAN, thereby giving you the fastest network speeds while freeing up bandwidth on the wireless channel for others. Lately however, I came across this bug when trying to connect to my Sophos VPN from a notebook - when the cable was connected, it works fine. When on wireless, it cuts out before completing the connection. Countless hours were spent checking if it was a Windows 10 issue (turns out, there is a windows 10 issue, but the resolution was to use the latest TAP driver from OpenVPN on top of the sophos VPN client)

Turns out, the OpenVPN TAP driver implementation on windows appears as a separate network card in the device manager:

When the connection is initiated it appears as though the LAN is plugged in, and WLAN switching will kill off the wireless network interface, as designed... Hence the connection never completes.

I disabled LAN/WLAN switching, and the connection completes as expected. Now to inform end-users to disable their WLAN when using LAN connections again...

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