MOBITEK EC20 4G router use SPI (Stateful Packet Inspection) Firewall for providing network security.

Go to “Firewall” -> “General”. In “Enable Firewall?” section, click on the button to turn on the firewall:-

Click “Apply”.

How does SPI Firewall work?

“… monitors active connections and checks whether incoming data packets correspond to these connections.
it then decides whether to grant or deny permission for them to pass the firewall.”
source: https://veepn.com/blog/what-is-spi-firewall/