1.Our router GL-E750 is intended to work ONLY in corporate VPN environment providing corporate’s address space towards WiFi. OpenVPN is used. OpenVPN server (in corporate Data Center) is connected to the Internet of course but not providing the Internet towards VPN tunnel.
2. If GL-E750 rebooted while VPN switch is OFF (and VPN Client is not activated), it gets 3G/4G Internet and it is possible to enable VPN and it will work as expected. Looking into logread I can see that initially GL-E750 is started with some strange time 21-Aug-2022 but later it is synchronized with the defined NTP servers.
3. However if GL-E750 rebooted while VPN switch is ON (and VPN Client is activated), GL-E750 is not able to get the correct time. It gets 3G/4G Internet and immediately opens VPN (as the client was activated before reboot). But here it is querying the NTP servers over VPN tunnel where we do not provide Internet - so GL-E750 failed to get the time, then OpenVPN client fails as well and not restarted (this is another issue, not for this post). Then I replaces the standard NTP servers IPs in /etc/config/system to IP of my OpenVPN Server where ntpd is also running. In that case I can see in tcpdump that the OpenVPN server provides the correct time in response to GL-E750 ntp query, but the box probably does with that nothing. As I said the time remains 21-Aug-2022 and the OpenVPN client fails in couple of minutes.