What is the Open Port Scanner? An open port scanner is a tool which is used to check the external IP address and identify open ports on the connection. It is used to detect whether the port forwarding is setup accurately or the server applications are being blocked by a firewall.
HowTo: UNIX / Linux Open TCP / UDP Ports - nixCraft Sep 03, 2010 Check If a Remote Network Port Is Open Using Command Line Feb 13, 2019 Open Ports on a Netgear Router(TCP/UDP) - VisiHow A specific port can support incoming traffic, outgoing traffic, or both. By default, Internet ports and LAN ports are closed so that traffic cannot flow through them. This could be the reason your online game is not connecting to the server. By default, a few specific ports like 21(FTP) and port 80 (http) are open for the computer to use. How to Get an Open Port on Netgear Routers
For opening a UDP port, type the following command: ★ iptables -A INPUT -p udp -sport portno -j ACCEPT where portno needs to be replaced with the numerical port number that you want to open. Here, we have assumed that you have logged in as the root user and have the superuser access. This should clear your concepts on how to open a port in Linux.
2. Run the below command to open incoming port. iptables -A INPUT -p tcp –dport portnumber -j ACCEPT. In the above command “portnumber” should be replaced with the incoming port number you wish to open. INPUT = INPUT means incoming traffic to the server. (The server port can be accessed from outside the server). An example is given below
How to open ports in Windows Firewall | Windows Central
How to Set Up Port Forwarding