Cannot bind to tcp port but no application listens to it

svachon

1/3/24, 10:42 PM

I am looking for a way to find out any process that may prevent binding to a port on a windows 10 machine.

My issue is that I have a server application that cannot open a socket on port 7777, sometimes it is 2809 that is blocked. The issue is not always happening, but it is reccurrent and even rebooting sometimes doesn't fix the problem. But at one point the problem disappears but then resurfaces randomly days or weeks later.

I tried:

tcpview: could not find any process using the port
netstat -anbo: could not find any process using the port
Telnet to the port, using all IPs ipconfig /all would return, no
connection to anything.
Created my own little java program to test binding on the port and make sure it's not a false negative, I am getting this result:

Address already in use: JVM_Bind

java.net.BindException: Address already in use: JVM_Bind
I used Wireshark to sniff the packets, can't find anything to that port.
Disable the firewall
Disable network adapters
Stop all Hyper-V related and Docker desktop services
Disable Anti-Virus
Rebooting

Still out of luck finding out what blocks this port.

Anyone has a suggestion?

887

1 + 0

networking

windows

tcp

Score:1

Server

Manu

1/4/24, 10:28 AM

Have you tried netstat, like this?

netstat -ano | findstr :7777

Otherwise you cloud try Resource Monitor > Network Tab > Listening Ports, if you prefer a GUI.

+ 5

svachon

1/4/24, 1:54 PM

Yes I tried this and no luck

Manu

1/4/24, 2:33 PM

if so, I'm pretty sure, your problem is not cause by the port being occupied. Can you name your server application and what is also hosted on this machine?

svachon

1/4/24, 2:54 PM

That's a local websphere app server that I use for dev purposes. It won't start when that port issue arises. But even after a reboot, sometimes I still have the port used, and I am not even running the WAS server, I simply run my Java test program to see if I can bind a socket to that port and I am getting the error. I am suspecting something is not releasing resources properly on the O/S which makes it think the port is still in use.

Manu

1/4/24, 3:42 PM

then I'd say your problem is not caused by a occupied listener. unfortunately I am not able to provide know how on these products or java

svachon

1/4/24, 4:20 PM

Thanks for trying to help, I plan to code another program in either .net or python that tries to listen on that problem port just to validate if it's a pure java/jvm issue or if the issue is system wide.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Cannot bind to tcp port but no application listens to it

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