1. install ufw

                  sudo apt update
                  sudo apt install ufw

                  sudo ufw enable

                  reboot

                  

2. Enbale iptables

                  sudo iptables -A INPUT -p <protocol> --dport <port_number> -j ACCEPT

                  eg:    sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
                  

List the rules

                  sudo iptables -L
                 

3. Allow ports

                 sudo ufw allow <port_number>/<optional_protocol>

                 eg: sudo ufw allow 8080/tcp              
                 

                

Add port range

                sudo ufw allow 50000:50100/tcp

reload the ufw

              sudo ufw reload
                

Check status

                sudo ufw status verbose
              

4. check the port

              telnet <IP_address> <port_number>

              OR

              nmap -p <port_number>  <IP_address>