Hi 
I have a zyxel LTE7490-M904 modem and noticed there seems to be some level of support, but only from this git commit :
In case someone here has installed openwrt on this model, I'm curious to hear how well/bad things are.
I don't have this model but its indoor counterpart,
what are you interested in knowing?
My router specs are the same as yours ...
I see that it lacks 5GHz wifi and has only one ethernet port but I assume the rest is completely the same ...
my router is:
your router is:
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Thanks 
This is good to hear and increases a bit my confidence.
Maybe what could be good to know is what packages you have that are important to manage the LTE part ? Do you use luci to check which signal metrics, bands, cells, and for managing LTE specifc things ?
Then one thing is that I need to prepare for is how to restore the zyxel firmware if things go wrong. I think this thread mentions it somewhere but forgot to bookmark the exact message, I have to dig a bit there (EDIT : found it here).
I assume the same procedure (note I have not tried it) that you see here (I'm happy with Openwrt and would never go back to OEM firmware):
none in particular I prefer the command line to see the various parameters of the LTE line example:
cat /root/cell_band
#!/bin/sh
LTEPROTO=$(cat /etc/config/network | grep "proto 'modemmanager'" | wc -l)
if [ ${LTEPROTO} -eq "0" ]; then
file1=$(mktemp)
ping -W 2 -c 1 9.9.9.9 > /dev/null 2>&1
picocom -t "$(echo -ne 'AT+QCAINFO\r\n')" /dev/ttyUSB2 --nolock --exit-after 300 --quiet --logfile $file1 >/dev/null
cat $file1
rm $file1
else
echo "Script not compatible with \"ModemManager\""
exit 1
fi
output
AT+QCAINFO
+QCAINFO: "pcc",100,100,"LTE BAND 1",1,65,-113,-8,-81,12
+QCAINFO: "scc",1500,50,"LTE BAND 3",1,65,-107,-11,-84,0
DL
+QCAINFO: "scc",1650,100,"LTE BAND 3",1,65,-103,-14,-80,0
DL
OK
or uqmi commands
uqmi -d /dev/cdc-wdm0 --get-signal-info; # modem into QMI
uqmi -m -d /dev/cdc-wdm0 --get-signal-info; # modem into MBIM
output
{
"type": "lte",
"rssi": -85,
"rsrq": -12,
"rsrp": -113,
"snr": 6.000000
}
ps: I assume that since the unit is positioned outside the house you will have a better signal in terms of SINR and RSPQ but it is only a hypothesis that can vary based on how far you are from the tower that emits the signal and any obstacles that are there
ps: since your router does not have a USB port that can accommodate a USB stick, if I were you this would be the list of packages to install (in addition to those already present):
at htop wget-ssl sed curl diffutils lsof usbutils procps-ng-watch coreutils-base64 flock lslocks picocom sms-tool qmi-utils luci-proto-qmi kmod-usb-net-cdc-mbim umbim luci-proto-mbim owut tcpdump openssh-client openssh-client-utils openssh-keygen
luci luci-ssl luci-app-uhttpd luci-app-firewall luci-app-https-dns-proxy pingcheck
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For the basics of the LTE part please refer to https://openwrt.org/docs/guide-user/network/wan/wwan/ltedongle
For the rest see
etc.
2 Likes
Great, now I just need to find the right timing to focus on that!
Now just to give a bit more context, my router modem is still inside as I want first to nail a good setup. The ambition with openwrt is to get rid of some limitations of zyxel's firmware, especially about the wifi part that seems to work only for management. Having openwrt ui would also be a huge win
I hope that with a trunk port, I could have a wan vlan with the lte interface bridged to my mikrotik router there, and then the wifi interface exposing 2 ssids (I have a dynamic vlan poc I'd to get on this device too)
If you want to use it in front of another router - do not install OpenWrt on it and forget about its WiFi.
As mentioned in this pull request,
The device is built as an outdoor ethernet to LTE bridge or router. The Wifi interface is intended for installation and/or temporary management purposes only.
This ethernet to LTE bridge is all what you need for your use case.
I suppose that even if you activate a 2.4GHz connection, its performance will be limited both in speed and by the wall between you and the external unit, but it will be possible to do it ...
example:
yes, that's ok. I see it more like an outdoor access point. Not sure how well the signal will travel downwards around the house, but I could get lucky, maybe 
f this is the premise then I suggest you to check / activate the "ip passthrough" mode on the OEM firmware so that any public IP address (if present or CGNAT) is passed to the router Mikrotik
ps: at the moment I can't give you certainty that the LTE module (modem) EG18 supports the mode "ip passthrough" on Openwrt firmware because in my case I'm behind CGNAT and I tried to look for documentation but I didn't find the correct way to set it on Openwrt
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I was (maybe naively) thinking that ip passthrough was equivalent to attaching the lte interface to a bridge 
I looked at that link and I suspect the solution might be to disable the dhcp client on wwan0 and run it on the lan side ? (that's how I do it currently without openwrt). But let's see, I hope I'll be able to tell soon
No need to waste time on this. I suggest using OEM firmware in "ip passthrough" mode as mentioned by @ncompact earlier.
Yes, I'm starting to digest all the readings you've linked above and it's a tad depressing 
But I'm not sure I'll be in peace having the zyxel sitting there with its weird UI and depriving me of that wifi chip. Maybe I could live with a double NAT setup (making some exceptions for a few vlans)
One thing unclear to me is whether the ip passthrough mode on the EG18 modem will necessarily be disabled after switching to Openwrt. I asked about that on the quectel forum here
There is no such mode for this modem.
Just open its AT commands guide and search for the keyword.
In your case "IP Passthrough" is a software feature provided by Zyxel.
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tl;dr; I agree - use the OEM firmware if you want IP passthrough
I'm probably going to confuse the subject even more now, but that's not 100% precise. There is an IP passthrough feature both in the Quectel EG18 module firmware and in the Zyxel LTE7490-M904 OEM firmware. The EG18 and the LTE7490-M904 are actually two routers in series, and both must implement IP passthrough to have the feature end-to-end.
Both the Zyxel firmware and OpenWrt depend on IP passthrough in the EG18 firmware. This does not change with OpenWrt, making the Quecel answer somewhat irrelevant.
You are referring to what happens to the LTE7490-M904 firmware, and there you are correct of course. OpenWrt does not currently implement implement "IP Passthrough" like the Zyxel firmware does. Zyxel use routing policies to implement the feaure, so there is no reason OpenWrt couldn't do the same. But it doesn't. And configuring the policies manually is not trivial.
Well, if you refer to IPPassthrough feature of mobileap app, then yes, it is available on many Qualcomm based modems but it is not easily accessible for users. And I don't remember if this actually works. Passthrough mode is also not configurable by AT commands on EG18 in contrast to RM5xx modems.
My understanding Zyxel implemented some sort of half-bridge mentioned in Bridge Mode - LTE USB Modem with modem probably running in regular QMI mode.
Yes. But this is IP passthrough. The modem is also a router.
We rarely care about it since most QMI modems are used in this mode (regardless of QMI or MBIM). But it becomes an issue when we want to do real layer 2 stuff. I never figured out how to do DHCPv6-PD with a Qualcomm modem for example. If you send an IPv6 link local packet towards the USB (or PCIe) side of whe modem, what will happen to it?