Problem solve Get help with specific problems with your technologies, process and projects.

Sometimes I get a message, 'port already open." What does it mean?

Sometimes I get a message port already open, when I try to connect to the Internet. What does it mean? How can...

I know which application is already using the net. I tried using task manager, but which one I couldn't tell.

The message received by your program or operating system indicated that a newly launched application is try to open a port that is already in use.

All programs that are network aware use IP Addresses and ports in order to communicate and transfer data. When a service runs on a server (i.e. Web server.) This service is bound to the IP Address of that machine which is, and "listens" for incoming connections on a specific port (80).

Firewall.cx logo

Do you have questions about networking, VPN security or VoIP? Then visit Firewall.cx, one of the few websites recommended by Cisco Systems in its world class Cisco Academy program.

Now, in order to resolve your problem, you need to identify which application is using the port for which your system is complaining. This can be easily done by downloading one of them personal firewall products (Zone Alarm is freeware and recommended) which will give you the ability to control which programs are allowed to initiate connections to the Internet.

If you would like to see what ports are being used, or listening for incoming connections, you can open your command prompt and type "netstat –a" and get a listing of the ports being used.

Alternatively, there is a freeware program I recently discovered called fport v2.0 (http://www.foundstone.com) that will show you the same results.

This was last published in September 2003

Dig Deeper on LANs (Local Area Networks)

Have a question for an expert?

Please add a title for your question

Get answers from a TechTarget expert on whatever's puzzling you.

You will be able to add details on the next page.

Start the conversation

Send me notifications when other members comment.

By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Please create a username to comment.