there any router in front of ZyWALL 310?
After check the log, it seems like ZyWALL 310
is behind a router.
ZyWALL 310 is behind NAT, The Local Policy setting here need to setup as the
WAN IP of the router.
to Configuration > VPN > IPSec VPN > VPN connection
click the “L2TP_VPN” to edit the rule.
is related discussion of behind nat settings
we have the remote access to the device and build up the tunnel to the device
to check why this symptom happens on your device since we can’t see the same
symptom in our lab?