The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer.

From @ifangyd via Twitter:

Hi, I've set up a classic virtual p2s network and a classic linux VM.  I've installed a SoftEther server.  SSTP works fine.  IPSec works fine if I vpn into the virtual network as it's listening at the private IP port (172.169.1.4:500 and 4500).

However, IPSec is not working connecting through VIP.  I've created end points for UPD port 500 and 4500.

It tried to connect and then says "The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer."

If I connect the virtual network and change IP to local IP, it works just fine.

Thanks

@AzureSupport