How can I know what is preventing my socket to bind to localhost:50060-50959

Question

I am using this Python code to listen to a port on my Windows 10 system:

import socket
for port in (50059, 50060, 50959, 50960):
  try:
    print(socket.socket(socket.AF_INET, socket.SOCK_STREAM).bind(('localhost', port)))
  except OSError as e:
    print(e)

However, it prints

None
[WinError 10013] An attempt was made to access a socket in a way forbidden by its access permissions
[WinError 10013] An attempt was made to access a socket in a way forbidden by its access permissions
None

meaning that I cannot access ports 50060 and 50959. I experimented further and confirmed that I cannot listen to any port in the range 50060-50959.

Update: After upgrading to Windows 10, 2004, it's port range 50060-59708 that is blocked somehow.

I would like to listen to port 50323, which falls into this range (in both cases).

I have tried netstat -aonq to find the culprit, but without success

C:\Users\bers>netstat -aon | grep :50
  TCP    0.0.0.0:5040           0.0.0.0:0              LISTENING       8008 (Connected Devices Platform Service)
  TCP    10.0.0.20:50985        51.105.249.223:443     ESTABLISHED     5208 (Windows Push Notifications System Service)
  UDP    0.0.0.0:500            *:*                                    4936
  UDP    0.0.0.0:5050           *:*                                    8008
  UDP    [::]:500               *:*                                    4936

Nothing else seems to be listening in this range. So why can't I? 50060-50959 is exactly 900 ports - I am sure this is no coincidence. (Update: Well, I was - it's 9649 ports on Windows 10, 2004.)

I have checked

• 10013 No socket could be created error, however nothing is listening on that port
• TCP/UDP ports that cannot be bound (permission error), but don't show up in netstat
• Determining what process has bound a port (without listening) on Windows
• https://stackoverflow.com/questions/48198/how-can-you-find-out-which-process-is-listening-on-a-port-on-windows

This means I have also tried netstat -q, see above, tcpview.exe, resmon.exe, and disabled Internet Connection Sharing (ICS).

Answer 1

If you face this issue on Win10 2004 that's because of an issue in this update, do the following:

netsh int ipv[46] set dynamic tcp start=49152 num=16384

reg add HKLM\SYSTEM\CurrentControlSet\Services\hns\State /v EnableExcludedPortRange /d 0 /f

I face this on opening Jetbrains IDEs and many other program that use sockets.