Sophos IPSec client on Lenovo L570 with Fibocom L831-EAU LTE modem doesn't work over mobile, but works over LAN/WiFi

Hi,

I'm facing problems on several newer Lenovo L570 laptops (containing "Fibocom L831-EAU" mobile broadband modems) when trying to use the Sophos IPSec client.

The notebooks run fully patched (OS and drivers) Win10 64bit systems (1709), but the problem also exists if I set up a new one out-of-the-box without any additional Windows updates (the one I tried ran on Win10 1703).

If I use a LAN or WiFi connection, everything works fine: I can establish VPN connections and transmit data over the tunnels.

If I use the mobile broadband connection, I can establish a VPN connection (all IPSec client icons are lit green), but as soon as the VPN claims to be ready, any connection to/from the public internet stops working (and transmitting over the tunnel doesn't work too).

According to the routing table, the default gateway has not changed, and the private IP ranges defined for the tunnel are correctly routed through my tunnel interface/IP.

Additionally, the IPSec client itself claims that it has lost connection to the internet (displays an intermittent line). The log also states that it doesn't receive DPD packets.

I tried several different notebooks (of the same model): it's not working on any of them. I successfully set up VPNs using the Sophos IPSec client on many older Lenovo notebooks in the past. The only relevant hardware difference seems to be the broadband modem (Fibocom): older models used a Sierra modem.

I tried several SIM cards and VPN profiles that do work flawlessly in other notebook models: none worked on the combination "L570 - Fibocom - Sophos IPSec client".

I tried an older version of the Sophos IPSec client (11.02): it didn't work either.

I tried using a different VPN client software (Shrew Soft VPN Client) on the L570 notebooks, mimicking the IPSec settings from the Sophos IPSec client profile: this does work, so I suppose it can't simply be a case of a bad modem driver. Maybe it's the combination that causes the trouble.

Has anyone else experienced similar problems?

Regards,
Björn

For reference: I also posted my problems to the Lenovo Forums where someone had a very similar problem using the Lancom VPN client and got it solved by an update.