1. Go to “Firewall” -> “MAC Filter”. In “MAC Filter Mode” section, select “Reject”:-
   
2. Under “MAC Filter List”:-
   • if the device is connected to the router, select the device from the dropdown list of “MAC Address”.
     
   • if the device is not connected to the router, type the MAC address of the device in “MAC Address” section.
     
3. Click “+” button then click “Apply” button.
   

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/

MOBITEK EC20 4G router can restrict device (client) based on MAC address but not IP address.

• The intended device (client) must be connected to MOBITEK EC20 4G router first so that it can appear in the client list of MOBITEK EC20.
• To check the client list, go to “Network Map” -> click “Client Status” -> check the IP address in “Client List”. Click “Refresh” if the IP address is not in the “Client List”:-
  
• To block the device, simply click the “cross icon” that belong to the IP address in the “Client List”:-
  
• You will get below popup message. Click “OK”:-
  
• The device is now in “Blocked Client List”. Click “Apply” to apply the changes made:-
  
• To unblock the device, just click the “add icon” that belong to the IP address in the “Blocked Client List”:-
  

• The default connection for MOBITEK EC20 router is 4G network. It will try to connect to 3G and 2G if the 4G network is unavailable:-
  
• MOBITEK EC20 can be configure to use different type of mobile network:-
  
• The preferred network that MOBITEK EC20 will connect to can be configured, here it 4G (LTE) preferred over 3G (UMTS), and preferred over 2G (GSM) :-
  
• The “4G signal” below indicates that the MOBITEK EC20 router is connected to 4G network with 5 bars to determine the signal strength.
  
• Alternatively, you can check which network MOBITEK EC20 router currently connected to, go to “Administration” -> click on “Console” tab, type “atcmd at+qnwinfo” (all small letters):-
  
  • first parameter is for “access technology selected”
    • for 4G, it can be:
      • FDD LTE
      • TDD LTE
    • for 3G, it can be:
      • TDSCDMA
      • HSPA+
      • HSUPA
      • HSDPA
      • WCDMA
    • for 2G, it can be:
      • EDGE
      • GPRS
      • GSM
  • the second parameter, “50219”, is the network operator (TELCO) (you can ignore this)
  • the third parameter is, “LTE Band 1”, the type of frequency/band selected (you can ignore this)
  • the forth parameter, 375,  is for “Channel ID” (you can ignore this)