How to check if a port is blocked on a Windows machine?

On the Windows platform, what native options to I have to check if a port (3306, for example) on my local machine (as in localhost ), is being blocked?

4 Answers 4

Since you are on a Windows machine, these things can be done:

Execute the following command and look for a «:3306» listener (you did not mention UDP/TCP). This will confirm there is something running on the port.

After this, if you are expecting incoming connections on this port and feel that the firewall may be blocking them, you could use start windows firewall logging and check the logs for dropped connections

• Go to Windows Firewall, Advanced settings
• Click on the Settings button next to «Local Area Connection»
• Select «Log dropped packets»
• Look at the log file location (if not present, define one)
• Click OK
• Now, when the connection attempt is made (assuming you know when this is done), look at the log file for a drop on port 3306.
• If this is seen, you will want to add an exception for this port.

There is one more command to check the firewall state
(Updated for Windows 7 users — as referred by Nick below — use netsh advfirewall firewall)

netsh firewall show state

• this will list the blocked ports as well as active listening ports with application associations

This command will dump the Windows firewall configuration detail

netsh firewall show config

If you have an active block (incoming connections are being dropped by firewall) after you start logging, you should see that in the log.

If you are running an application/service that is listening on 3306, the firewall config should show it to be Enabled. If this is not seen, you have probably missed adding an exception with the firewall to allow this app/service.

Finally, port 3306 is typically used for MySQL. So, I presume you are running MySQL server on this windows machine. You should therefore see a listener for 3306 accepting incoming connections. If you do not see that, you need to work with your application (MySQL) to get that started first.

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How to Determine What Ports are Being Used in Windows 10

Last year we suffered the BitCoin miner virus which locked our computer and levied a ransom. And yet, the main reason for the spread of the virus was that the unused ports did not close. So, to guard against happening again, we have to determine what ports are being used in windows and then turn it off.

What is a Port?

When it comes to port, it’s necessary to talk about IP as well. Let me draw an analogy to describe the relationship between the Port and IP. Once upon a time, if you want to send a letter to your friend in a faraway place, you need to write down your address and his address on the envelope. The envelope is amount to the data package while both addresses are amount to IP. When the postman sends the letter to your friend’s house, and if your friend opens the door to get it, now the door is equal to the port. If your friend doesn’t open the door, that is to say, the port closed. After that, the letter will be sent back to you. In network technology, ports divide into two classes. One is a physical port, such as USB port. The second is the logical port, which generally refers to the port in the TCP/IP protocol. These port will cause some virus and harm your PC. As a result, there is necessary to check if the port is open.

Determine What Ports are Being Used in Windows 10

Step 1: Hit Windows + R to invoke Run dialog and type cmd to open Command Prompt.

Step 2: Type netstat -ano to list states of all ports.

Alternatively, type telnet

to check if port is open.

Step 3: Locate to the target port and view the corresponding PID in the final column. For example, the PID of port 2179 is 3800.

Step 4: Input tasklist|findstr “3800” and hit Enter on the keyboard to view which service takes up the port.

Step 5: To end up this service, run taskkill /f /t /im vmms.exe.

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How do I check whether an open port is TCP or HTTP?

Specifically, I have a Windows server (Windows 7), but the netstat -an command only shows whether ports are TCP or UDP. I thought these were the only kinds of ports, but node.js seems to distinguish between HTTP ports and TCP ports (example at bottom of linked page). I’m currently using node.js in a program that will run on my server, and it opens HTTP ports by default. These appear as TCP ports under netstat -an .

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Is there a command line trick for distinguishing whether an open port on this server is HTTP or TCP? I make requests to my Information Technology office about ports that I need on this server, and they need to know whether these ports will be TCP, UDP, etc.

If necessary to use a remote client, I have a Mac that can do the job.

2 Answers 2

All HTTP traffic is transmitted over TCP Ports. I think what may be causing some confusion is that the first node.js example uses the http module and the second example uses the net module.

The http module is built on top of the net module (which handles the TCP layer underlying HTTP).

Only one process can bind to a port. If you’re having difficulties connecting, shut down any other applications that may be using the same port, such as your Java Hello World server. Run netstat -an to make sure you don’t see the port listed that you’re trying to listen on in you node.js TCP server (port 1337) in the example. If nothing is listening on the port, fire up your node.js TCP server and run netstat -an again to make sure it’s actually listening on the intended port.

Another suggestion — temporarily turn off the software firewall then use the telnet client on the local server to attempt to connect to the port using the command telnet 127.0.0.1 1337 (replace 1337 with your port) from the command prompt. This will eliminate any network devices such as firewalls between the client (telnet in this case) and the server. If the screen goes blank, you’ve connected. If you get the message Could not open connection to the host, on port then it’s still not listening on the TCP Port. If you can connect locally from Telnet but you cannot connect remotely then there is something blocking your connection.