Are you wondering about the ports opened on your PC? Or maybe some specific program uses some specific port, and you need to know what port is it using. You can easily perform a simple check of the ports using the command prompt. If you want an easier way, there are plenty of programs for this purpose, but I will show you how to check open ports online in Windows 10/8/7 without installing any third-party program.
What are Ports?
A portion of memory is used for data transfer on the Internet or any other computer network. Ports are identified by transport layer port number assignments or sometimes called “well-known ports.”
Physical connections are not associated with ports; they are only logical channels for transferring data between computers on a network. For example, all servers listen to specific port numbers for incoming client requests for access to files or databases stored on the server’s hard disk drive (HDD).
Computers usually have thousands of ports assigned to them. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) govern port assignments and use.
Routers and firewalls group together individual applications that require data transfer at a certain port number into one entry in their configurations. For example, if two different applications use port 3456, only one entry must be added to the router or firewall configuration for both services rather than having two separate entries for each service. How specific these groupings get is up to the administrator of either a router or a firewall device.
Some familiar examples of common Internet services include:
- HTTP uses port 80
- HTTPS uses port 443
- FTP uses ports 20 and 21
- IMAP uses port 143
- POP3 uses port 110
- SMTP uses port 25 and 587
- DNS servers use port 53
What is an Open Port?
An open port is a TCP or UDP port that has not been assigned to any application and thus remains a listening port, ready for incoming connections.
A blank TCP/UDP client-side port number on your computer (or called the host) will send out electronic messages in search of connection or conversation. The message tells other computers to come to talk to this machine using the following process:
Machine 1 sends out an electromagnetic signal with its IP address saying, ‘Hey! I’m Machine 1! If you’re looking for me, here’s my IP!’
Skype would be an example of one of these applications. Skype constantly scans for ports, looking for responses from other machines. If it receives a signal and can correctly determine that the port is open and not in use by another application, Skype will attempt to connect with the remote computer on those ports.
In this situation, Machine 1 sends out electromagnetic signals saying, ‘Hey! I’m Machine 1! If you’re looking for me, here’s my IP!’
Machine 2 picks up this signal and returns an acknowledgment. This tells Machine 1 that Machine 2 has also received the message.
Both computers now know each other’s IP addresses and can begin communication.
How To Check Open Ports Online With Windows 10 Tutorial
Note: The procedure described below works only on Windows systems.
Just copy and paste the code given below into notepad and save it as port.bat (i.e., save it with .bat extension.)
netsh firewall show state netsh advfirewall firewall show rule name=all netsh advfirewall export “C:\Users\username\Desktop\port.txt” exit
After saving this file, run it (double click), and ports will be displayed on your computer.
This is how you can easily check which ports are opened on your Windows PC using the command prompt. This technique works only if there is an Internet connection working.
Alternative Method: There is yet another way to check ports. Open the command prompt and type netstat -aon, and press enter. This will display all open ports on your computer.
Note: Please remember that if you close some ports using the above method, it will not affect any installed program. Closing some ports may cause some programs to be unable to work correctly. So always use netstat -aon command first if you want to close any port.
You can also check what process is using which port here. After performing this simple task, if there are no errors or problems, you can safely assume no open ports. If, by chance, your PC displays an error message like “the port is already used by another application or service,” then it means that some other program is using the port. You can safely ignore this error message if there are no problems with your system.
Using an Online Port Checker:
Using a site like this one – openport – can help you to check open ports online, you can give it a port number and it will tell you if the port is open or closed.
Anyway, I hope you find this tutorial helpful.