I would recommend ECM mode if you are using the RJ45 board by Ethernet. Seems to be pretty stable. Any other usbnet mode you need to make sure AT+QMAPWAC=1 or it won’t auto connect the radio to the rest of the interfaces. In ECM this just happens automatically.
AT+QCFG=“usbnet”,1
then reboot
If you used the AT+QETH=“RGMII” command… don’t use that.
I’m still in the process of confirming it but I think that’s what was causing my Ethernet port on the RJ45 board to stop responding in certain scenarios.
Run AT+QETH=“RGMII” to check it. If it says ENABLE run AT+QETH=“RGMII”,“DISABLE”,1
then reboot
For IP passthrough there’s 3 levels of IPPT
- DMZ method (not a true IP passthrough)
Set the modems DHCP to only hand out one IP address with AT+QMAP=“LAN”,192.168.225.2
If that errors on you then you don’t have that command on that firmware revision so use this to define the whole dhcp range and gateway AT+QMAP=“LANIP”,192.168.225.2,192.168.225.2,192.168.225.1,1
Then, set that IP as the DMZ with
AT+QMAP=“DMZ”,1,4,192.168.225.2
-
Actual IPPT
AT+QMAP=“MPDN_rule”,0,1,0,1,1,“FF:FF:FF:FF:FF:FF”
If you want the DNS from the provider to pass through as well: AT+QMAP=“DHCPV4DNS”,“disable”
You should still be able to access 192.168.225.1 if you have a web server running on the modem still. -
I haven’t messed too much with this yet because it disables local access to the gateway address (192.168.225.1) but it’s the final step to a true IPPT mode.
AT+QMAP=“IPPT_NAT”,0
First time I ran that I went…oh crap I can’t access my admin page any more! 
(I have a webserver running on the modem serving a management page that accepts AT commands and shows signal stats)
P.S. If you run AT+QMAP=“WWAN” it’ll show you both the IPV4 and IPV6 address assigned from the carrier.