What is the best port to choose in dfx replica to avoid port clash?

[q2333gh]

I have search the web says : <1024 is for core services. <49152 is reserved by IANA . So best choose between 49152 through 65535 ?

/home/btwl/.config/dfx/networks.json

{

    "local": {
      "bind": "127.0.0.1:50010",
      "type": "ephemeral",
      "replica": {
        "subnet_type": "system"
      }
    },
    "ic": {
      "providers": ["https://ic0.app/"],
      "type": "persistent"
    },
    "ic_test": {
      "providers": ["https://ic0.app/"],
      "type": "persistent"
    },
    "web_test": {
      "providers": ["https://ic0.app/"],
      "type": "persistent"
    }

}

[ericswanson-dfinity]

It turns out that using a port between 49152 and 65535 doesn't always work, because those ports can be used as ephemeral ports. In other words, dfx start might work today because port 50010 happens to be available, but fail tomorrow because some other process on your system is using the port.

See https://www.rfc-editor.org/rfc/rfc6335.html section 8.1.2, specifically:

On the other hand, application software MUST NOT
assume that a specific port number in the Dynamic Ports range will
always be available for communication at all times, and a port
number in that range hence MUST NOT be used as a service
identifier.

Here are two options:

1. Use an unassigned User Port (between 1024 and 49151), which can be found at https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml
2. Use a Dynamic Port, by specifying port 0 in the bind address:

$ cat ~/.config/dfx/networks.json 
{
  "local": {
    "bind": "127.0.0.1:0"
  }
}
$ dfx start --background 
Running dfx start for version 0.16.1
Using shared network 'local' defined in /Users/ericswanson/.config/dfx/networks.json
dfx info webserver-port
Initialized replica.
Dashboard: http://localhost:57672/_/dashboard
$ dfx info webserver-port
57668

[q2333gh]

Thank you so much for detailed and expanded explanation.
Make a pretty clean and clear answer about what port to use for a regular program.
And I really like the way you answer the question and try to learn the reply method from in it !