How to determine which program uses or blocks specific Transmission Control Protocol ports in Windows Server 2003

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

For a Microsoft Windows XP version of this article, see 281336.

Original product version:   Windows Server 2003
Original KB number:   323352

Summary

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 particular 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). With this feature, you can find the specific port that a program currently uses. Because a program already uses this specific port, another program is prevented from using that same port.

How to match the process ID to a program

To match the process ID to a program, follow these steps:

  1. Press Ctrl+Alt+Delete, and then click Task Manager.
  2. Click the Processes tab.
  3. If you don't have a PID column, click View > 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 PIDs. You should be able to easily find the process ID and match it to the program that is listed in Task Manager.

How to obtain additional information about the Netstat.exe utility

To obtain additional information about the Netstat.exe utility, follow these steps:

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