I have a Linux-based OS (Rasbian) running on Raspberry Pi 2+ and it is using Huawei E3372s 4G/LTE USB Stick for internet connection.
All my outbound connections work perfectly (Huawei USB mode changed using usb_modeswitch-ruling and Udev/rules.d) but I am unable to receive any kind of inbound connection to the Raspi. Incoming is just not working.
I cannot receive any packets or connections, which I have tracked realtime and from logs using tools provided by Raspbian package distributions.
I have already confirmed with my 4G ISP that the extended service which allows two-way traffic is enabled, reseted and so much of their knowledge, to my 3G/4G subscription, working perfectly from their end but I am unable to receive any packets with the Raspi.
Huawei E3372s (unlike most of the older sticks which use dialing like
wvdial) uses CDC_ETH driver system which creates an ethernet-like device to the system (ETH1 in this case) and should work in this case flawlessly.
I have cleared, re-created, tested, modified, re-cleared and again done all needed tasks with IPTables, checked, modified and tested Route several times as well as confirmed that there are no known blocking systems preventing connection through Huawei USB-stick, yet I still cannot receive even Ping to my system, although there are fully functional services running.
I have also checked more simple and straightforward areas such as hosts allow/deny rules and have had no luck with them. It is not APN name either as all settings with the Huawei's internal configuration have been set correctly using it's web interface.
I have, however, encountered on few occasion from random forums, that Huawei CDC_ETH solution may have flaws handling incoming connections with its driver.
If any of you have experience with Debian/Rasbian/Linux incoming connection problems with Huawei E3372s or relative 3G/4G USB product which use CDC_ETH and have found solution to this problem