Hi, as found in this thread: Differences with Mobile Modes (NAT, Bridge, Passthrough)
Passthrough mode
In this mode the router shares the IP address assigned by the operator with a single LAN clients. Great option in cases where the router needs to have internet access itself (for example RMS, ping reboot, monitoring, etc.).
I don’t believe it’s necessary for you to set up passthrough or bridge modes, as connecting end devices to the LAN ports of the Teltonika device should already provide internet.