This article discusses how to determine which program uses or blocks specific Transmission Control Protocol (TCP) ports.

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The Netstat.exe utility has a new switch, the -o switch, that can display the process identifier (ID) that is associated with each connection. This information can be used to determine which process (program) listens on a given port. For example, the netstat -ano command can produce the following output:

Proto    Local Address    Foreign Address    State        PID
TCP      0.0.0.0:80       0.0.0.0:0          Listening    888
				

If you use Task Manager, you can match the process ID that is listed to a process name (program). This feature enables you to find the specific port that a program currently uses. Because this specific port is in use already by a program, another program is prevented from using that same port.

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To match the process ID to a program

1.	Press CTRL+ALT+DELETE, and then click Task Manager.
2.	Click the Processes tab.
3.	If you do not have a PID column, click View, click Select Columns, and then click to select the PID (Process Identifier) check box.
4.	Click the column header that is labeled "PID" to sort the process by their PIDs. You should be able to easily find the process ID and match it to the program that is listed in Task Manager.

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To obtain additional information about the Netstat.exe utility

1.	Click Start, and then click Run.
2.	In the Open box, type: cmd, and then click OK.
3.	At a command prompt, type: netstat /?.

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