USB modem not connecting with latest Merlin (HUAWEI dongle)

[Nazgulled]

I have an AC68U and a HUAWEI E3276s-150 (not HiLink, as far as I am aware) 3G/4G dongle connected to the ASUS router. I am from Portugal and my ISP is Vodafone, as such, my APN is "internet.vodafone.pt". I am currently using the Asuswrt-Merlin 374.42_2 firmware version with Dual WAN turned on (Primary WAN: Disconnected; Secondary WAN: Connected).

This is working but I have to manually issue the following commands (I did it through SSH):

echo -e "AT^NDISDUP=1,1,\"internet.vodafone.pt\"\r" > /dev/ttyUSB0
udhcpc -i usb0 -p /var/run/udhcpc1.pid -s /tmp/udhcpc

I haven't yet tried placing the above code in a user script but I'm assuming it will work just the same.

I'm happy that I finally got this working but I'd rather be using the latest Asuswrt-Merlin 378.56_2. However, the above procedure didn't work for me.

Did anyone got it working with the latest version or is everyone still on older releases? What am I doing wrong?

 

[Nazgulled]

I tried without Dual WAN, having a single WAN set to USB and this also worked with the commands above.

I've also tried one more time with Asuswrt-Merlin 378.56_2, but I can't get it to work in the same way. I've read a few posts where some people didn't even need the commands above as long as they were using Dual WAN mode on the USB3 port, tried this, didn't work too. But with this firmware version and the commands above, I can get past the first one, but not the second one:

admin@RT-AC68U-9828:/tmp/home/root# udhcpc -i usb0 -p /var/run/udhcpc1.pid -s /tmp/udhcpc
udhcpc: SIOCGIFINDEX: No such device

What am I missing?