L2TP/IPsec stopped working in Windows 11 / Windows 10
Issue
Windows 11 PCs suddenly stopped connecting to L2TP/IPsec VPN hosted on SonicWall firewall. The following error is displayed immediately after clicking Connect:
Can't connect to VPN
The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer.
Read more: L2TP/IPsec stopped working in Windows 11 / Windows 10