Port not shown to be used in netstat, but trying to use the port is denied by Windows

I found the answer to this problem already and just want to document my finding.

In one of my recent project, I found that a port would not be shown as being used in netstat, but when my project tried to use the port, an error would be thrown.

For example, let's say I want to use port 53000:

netstat -ano | findstr :53000

Nothing would be shown, but if I attempted to use the port in Node.js, a permission error will be thrown.

Solution

It turned out that things such as Hyper-V, Docker, etc would reserve a range of ports. To find out the ranges of ports reserved, do the following:

netsh interface ipv4 show excludedportrange protocol=tcp

In my case, I would see something like this:

Protocol tcp Port Exclusion Ranges

Start Port    End Port
----------    --------
     49805       49904
     50000       50059     *
     50060       50159
     50160       50259
     50360       50459
     50870       50969
     50970       51069
     51070       51169
     51270       51369
     52353       52452
     52453       52552
     52553       52652
     52653       52752
     52853       52952
     52953       53052
     53053       53152
     53324       53423
     56247       56346
     56347       56446
     56547       56646
     56647       56746

* - Administered port exclusions.

To fix my problem, I can:

Disable Hyper-V
netsh int ipv4 add excludedportrange protocol=tcp startport=53000 numberofports=1 (as administrator)
Enable Hyper-V