Problem: Mobile Mode doesn't support L2TP or PPTP VPN connections

Recently my ADSL filter between the phone line and the TELSTRA SMART MODEM GEN2 failed and caused my internet connection to fail over to "mobile mode" or "backup mode" which I believe is a SIM card in the modem that auto-connects to the internet via the local mobile network when the main ADSL or cable service is unavailable. After this happened the first thing I noticed is I couldn't connect to PPTP or L2TP VPNs. Once I resolved the problem with the filter and connected via ADSL to the internet then the VPN's started working

Cause: Telstra Smart Modem Gateway in mobile mode don't support PPTP or L2TP VPNs

I'm just putting this here as a warning that the mobile mode connection doesn't seem to support creating PPTP or L2TP connections.

If you are working from home and attempting to dial your VPN unsuccessfully and you are using Telstra Modem check that you are not in mobile mode.

Work-a-round: Hot spot your mobile

I have worked around the problem by hot spotting my laptop to my Telstra mobile phone service as this allows PPTP or L2TP connections.

Work-a-round 2: Use OpenVPN

I have tried an OpenVPN connection to the same remote site and it works when the Telstra Smart Modem is in mobile mode

The errors you see from Windows 10 when trying to start L2TP or PPTP connections appear as follows