Hi-link e3372h-320 with Freshtomato

In the configuration interface of the dongle (192.168.8.1),  locate the DMZ settings (Settings > Security > DMZ settings) and enable the DMZ feature with a target IP address of 192.168.8.100, which should be the IP of the eth1 network interface on the router that the dongle is connected to (double check in OpenWRT under Network > Interfaces > eth1 > IPv4 or in the Basic->Network or Status->Overview in Freshtomato). Form now on, all incoming connections are passed directly to Freshtomato/OpenWRT. The firewall, SIP, and UPnP features of the dongle can be disabled. In contrast to what other guides say, the NAT setting can stay at its default (cone), because it does not have any influence on the DMZ behavior.

 Important!

Do not forget to put the Watchdog Mode as Ping, otherwise it will be disconnecting after a day.

From here:

https://protyposis.net/blog/using-the-huawei-e3372-hi-link-lte-dongle-with-openwrt/