pyftpdlib runs but doesn't seem to be listening on port yet other ftp server apps work

Question

I'm trying to build an ftp server running in Python on Windows. I took the basic example for pyftpdlib, as you see below.

import os
from pyftpdlib.authorizers import DummyAuthorizer
from pyftpdlib.handlers import FTPHandler
from pyftpdlib.servers import FTPServer

def main():
    # Instantiate a dummy authorizer for managing 'virtual' users
    authorizer = DummyAuthorizer()

    # Define a new user having full r/w permissions and a read-only
    # anonymous user
    authorizer.add_user('user', '12345', "c:\\temp", perm='elradfmwM')
    authorizer.add_anonymous(os.getcwd())

    # Instantiate FTP handler class
    handler = FTPHandler
    handler.authorizer = authorizer

    # Define a customized banner (string returned when client connects)
    handler.banner = "pyftpdlib based ftpd ready."

    # Specify a masquerade address and the range of ports to use for
    # passive connections.  Decomment in case you're behind a NAT.
    #handler.masquerade_address = '151.25.42.11'
    #handler.passive_ports = range(60000, 65535)

    # Instantiate FTP server class and listen on 0.0.0.0:2121
    address = ('', 21)
    server = FTPServer(address, handler)

    # set a limit for connections
    server.max_cons = 256
    server.max_cons_per_ip = 5

    # start ftp server
    server.serve_forever()

if __name__ == '__main__':
    main()

When it runs/executes it seems to be waiting, nothing else is using port 21. See output below from its process.

[I 2017-04-17 19:05:55] >>> starting FTP server on :::21, pid=43124 <<<
[I 2017-04-17 19:05:55] concurrency model: async
[I 2017-04-17 19:05:55] masquerade (NAT) address: None
[I 2017-04-17 19:05:55] passive ports: None

But from a remote windows host I cannot telnet to port 21 on the host where pyftpdlib script is running. I have another separate standalone ftp server .exe for windows running and it works fine I can telnet from the remote windows host to port 21 on the host I can't get pyftpdlib to run properly on it, so I know it's not any FW or network issues.

I'm really scratching my head on why this module pyftpdlib won't work.

Answer 1

Maybe it's because it's listening on an IPv6 address. Try to change this:

address = ('', 21)

to this:

address = ('0.0.0.0', 21)