I have a very simple problem, but the methods I've used in the past do not seem to be working in this case. I am attempting to teach myself network coding in Java, which requires connections between computers. For this reason, I've tried opening/forwarding ports on a certain computer acting as "the server".

Windows 8, Verizon FiOS router, firewalls disabled, port X forwarded from router to device.

Both the top two hits for "Open port checker" in google say that the port is not open (one says further: Connection Refused).

My router firewall is at low settings (all inbound and outbound accepted minus the spam port 25), the port X is forwarded to my device (and says Active on the router config page), and my W8 device has its Windows firewall disabled. (None other ever installed).

Am I doing something wrong? I used to do this all the time for gaming, but it's been a few years and I'm doubting myself.

Thank you for your help, AK

  • What's the port number?
    – rtf
    Commented Jan 27, 2013 at 19:50
  • @Tanner I tried 513 (randomly came up with it) and then tried 44444 (from the tutorials). Both TCP. Both seem to have the same issue. Commented Jan 27, 2013 at 21:15
  • 1
    Was your program running and was the port opened by it during your test?
    – rtf
    Commented Jan 28, 2013 at 0:55
  • @Tanner Well, I think the test that caused me to look into this issue - yeah that was the case (which is dumb in retrospect). However, now I am using online port checkers and the Angry IP Scanner you suggested. Commented Jan 28, 2013 at 1:04
  • oh hmmm now I get what you're saying. Absolutely makes sense. Let me give it another shot and get back to you. Commented Jan 28, 2013 at 1:06

1 Answer 1


It might be easier to test your code on your own network rather than fighting with a router and your ISP's firewall.

You can check if the port is open on your machine by using a simple port scanner. Something like Angry IP Scanner or Nmap will do this quite handily.

The port will appear closed unless your program has opened it. Make sure your program your program is listening on that port.

For a super simple test, try using telnet. This is installed by default on XP. For Windows 7 go to add 'Add/Remove Programs', select Add Features, and install Telnet Client. Now you can open a command prompt and simply type 'telnet [port number]' to test the connection and see its output. Replace with the test PC's address if running the command from another computer on the network, or replace with your public IP to test from the Internet.

And for what it's worth, port 25 isn't the "spam port", it's for SMTP. Unless you're running a mail server you have nothing to worry about.

  • Thank you for the response! I thought about that, but I doubt the ISP is blocking my ports due to the fact that 1) FiOS is known for its lax port blocking policies, and 2) when I run your suggested Angry IP Scanner, both those ports fail to show up as open even when it is run on the machine itself. Again thanks for looking into it though! Commented Jan 27, 2013 at 21:49
  • Absolutely moronic misunderstanding of the fundamentals on my part - program has to have the socket open for it to appear open from outside ugh. Thanks so much for your help! Commented Jan 30, 2013 at 5:31
  • @AK4749 Haha took me a while to realize that might have been the problem. Glad you figured it out.
    – rtf
    Commented Jan 30, 2013 at 15:00

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