Workaroud for Microsoft Update Breaking SonicWALL L2TP VPN?

ddc

Microsoft's January 2022 update breaks L2TP VPN for some, including SonicWALL.

https://docs.microsoft.com/en-us/windows/release-health/status-windows-10-21h2#2773msgdesc

Microsoft suggests the workaround of disabling the "Vendor ID" at the server end, and notes that this is option is not available for all. Is it available for SonicWALL L2TP VPN? I'm guessing not, or at least not in all cases, since the Vendor ID is referenced as used when NAT Traversal is enabled:

https://www.sonicwall.com/support/knowledge-base/what-does-the-nat-traversal-checkbox-do/170505260803073/

Thanks

scottkeen

I'm just confirming that L2TP VPN connection from my Windows 10 PC to my SonicWALL TZ 670 is broken, as of the last couple of days, about January 13th.

I'm also looking for how to disable the Vendor ID in SonicWALL L2TP VPN as a workaround.

For the time being, I've uninstalled the Microsoft update which broke L2TP VPN

1. Start elevated Command Prompt, Run as Administrator
2. Type wusa /uninstall /kb:5009543 to remove the Windows Update KB5009543 which broke L2TP VPN
3. Change Windows Update to pause for the maximum 7 days, maybe Microsoft will fix this update by then
4. Restart PC

After doing this, I'm able to connect with L2TP VPN but this is only a temporary fix until Microsoft fixes what they've done.

Bear in mind that uninstalling update KB5009543 also removes security patches and other fixes that were installed with that update.