ublox TOBY L200 TLS not working

[Martin Kelly]

Hi,

I'm testing on master with a ublox TOBY L200 using the RNDIS interface. 
I'm finding that I can ping reliably (~100ms latency to Google), and I 
can access HTTP and FTP. However, the moment I try anything with HTTPS 
or TLS, I just get timeouts. In wireshark, I'm seeing a lot of TCP 
spurious retransmission and TCP Dup ACK.

Additional notes:
- I'm using router mode.
- I'm using T-Mobile in the USA.
- Switching to the ECM interface works, but the speed is low (~500kbps, 
3G, on a connection that can do ~5mbps using a different modem).
- Disabling the "RNDIS driver optimization" (AT+UDCONF=67,0) fixes the 
issue but results in the same slow (~500kbps) speeds.
- I noticed someone on the ublox forum had a similar-sounding issue that 
they claim was caused by some regression in a 4.9 kernel. Their issue 
was also fixed with AT+UDCONF=67,0 but they did not mention if the 
performance changed. Full details here: 
https://forum.u-blox.com/index.php/16851/mpcie-toby-l210-02s-not-working-with-newer-linux-kernel
- I saw identical behavior on the L201.
- In case it matters, I'm on Debian Stretch with a 4.9.88-1+deb9u1 kernel.

Any idea what might be wrong? Is anyone else seeing this, or are you 
seeing high speeds on the TOBY L2 with RNDIS?

Thanks,
Martin