TCP/IP Check used ports in Windows 11 or Windows 10

If you try to open a TCP port, but this port is in use, an app on your computer is using this port.

Every app that makes a network or internet connection in Windows communicates via 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, which communicates back with “packets”.

To communicate, a port number is often used by an app. It is this port that the app communicates with. In Windows you can find out which app is using which port. This is useful, for example, to know which port(s) are in use with which app(s). By closing or deleting the app, you can still use the port for another app.

There are many reasons for wanting to know the port number of an app. In general it concerns network or solve internet problems. This article explains how to check the port number in use by an app.

TCP/IP Check used ports in Windows 11 or Windows 10

There are several ways to check open ports used by an app. In this article I offer you two ways, the first is through 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:

netstat -ab

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 find listening ports (in use) by an app is through the help of software. There is a lot of software available that makes the display of netstat easier to read.

The most commonly used tool to display open ports per app is Sysinternal TCPView.

TCPView is a Windows program that shows you detailed lists of all TCP and UDP endpoints on your system, including the 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. TCPView provides a more informative and well-organized subset of the Netstat program that comes with Windows.

Download Sysinternals TCPView

Open TCPView. In the “Local port” column you will see all local open ports. On the left you will see “Process name”. This is the process name of the app 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 of which can be found as a column. This is the IP address and port used to communicate with the other device that is connected.

On the far right you will find the “module name”, a reference to the module in which the process is located.

I hope this has helped you trace open ports in use on your computer back to an app or process name. Thank you for reading!

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• How to create a network connection in Windows 11.
• Who is on my Wi-Fi network?
• Install and manage Microsoft IIS web server in Windows 11.