If you try to open a TCP port, but this port is in use, then an app on your computer is using this port.
Every app that connects to the network or Internet in Windows communicates using a protocol. In most cases, this is the TCP protocol. TCP means Transmission Control Protocol, and its purpose is to send “packets” to another computer, usually a server. Then, it communicates back with “packets.”
A port number is often put into use by an app to communicate. It is this port that the app communicates with. In Windows, you can look up which app uses which port. This is useful, for example, to know which port(s) are in use by which app(s). By closing or removing the app, you can still use the port for another app.
There are many reasons one might want to know the port number. In general, it is to solve network or Internet problems. In this article, you will read how to check the port number used by an app.
How to find Ports that are in use by an app in Windows 11 or Windows 10
There are several ways to check open ports used by an app. In this article, I will offer you two ways. The first is using netstat.
Click on the Start button. In the search box type: command prompt. Then right-click on the Command Prompt result and click “Run as Administrator”.
In the Command Prompt window, type the command:
You will now see a result with protocols (TCP or UDP), process names, IP addresses, and port numbers in use by the process.
The second way to lookup listening ports (in use) by an app is through the help of software. But, again, there is a lot of software available that makes the display of netstat easier to read.
The most common tool used to display open ports by the app is Sysinternal TCPView.
TCPView is a Windows program that shows you detailed lists of all TCP and UDP endpoints on your system, including local and remote addresses and the status of TCP connections.
On Windows Server 2008, Vista, and XP, TCPView also reports the name of the process that owns the endpoint. In addition, TCPView provides a more informative and convenient subset of the Netstat program that comes with Windows.
Open TCPView. You will see all local open ports in the “Local port” column. On the left side, you will see “Process name.” This is the process name of the app that is using the port.
To filter more specifically, you can use the “Protocol” column. This shows whether the TCP or UDP protocol is used.
Then you can filter the “State” column. The “State” listening means that the port is in use and listening for an incoming connection. “Established” means that the port is also in use but has established a connection with the “Remote address” and the “Remote Port”, both found as columns. This is the IP address, and port used to communicate with the other device connected.
You find the “module name” on the far right, referencing the module in which the process resides.
I hope this has successfully traced open ports on your computer that are in use back to an app or process name. Thank you for reading!