The L2TP works on my ISP Modem.
I only get this error on the "QoS" page, when I'm trying to interact/update the values with "Congestion Control" and "Bandwidth Allocation". I get the same error in both of them.
I'm connected via Coax Cable by 2 different ISP, which means I can switch between DHCP and L2TP connection and get different Routing.
I use the L2TP because the Line feels much more "clean" than the DHCP.
FPS competitive games play smoother with better Register-hits and the Server-side updates on the animation feels more responsive / less delayed than what I get with DHCP connection.
(I think it's less congested routing that relay packets much more "cleanly" by giving- less jitter / less out-of-order udp packets / more stable ping flactuation)
My issue is that I want to midigate any Bufferbloat with the L2TP connection to see if there will be an improvment.
As you can see, it's kinda ass when I test the "Connection Benchmark".