ls command in ftp> not working!

Question

I was practicing ftp but faced an issue: ls command isn't working on ftp> . Why? I checked on 2 remote servers but ls didn't work on either and gave different output when ls was executed. Please see below for the 2 remote boxes.

The below shows my remote server where I installed vsftpd today.

ravbholua@ravbholua-Aspire-5315:~$ ftp rs
Connected to ravi.com.
220 (vsFTPd 3.0.2)
Name (rs:ravbholua): 
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> pwd
257 "/home/ravbholua"
ftp> ls
500 Illegal PORT command.
ftp: bind: Address already in use
ftp> 

The below is for a different remote machine where I have to send some files. But as ls on ftp> isn't working, how will I transfer files from my local box to that box because I can't be confirmed without ls whether the files have been transferred or not.

ravbholua@ravbholua-Aspire-5315:~$ ftp 125.21.153.140
Connected to 125.21.153.140.
220---------- Welcome to Pure-FTPd [TLS] ----------
220-You are user number 1 of 10 allowed.
220-Local time is now 04:34. Server port: 21.
220-This server supports FXP transfers
220 You will be disconnected after 2 minutes of inactivity.
Name (125.21.153.140:ravbholua): peacenews
331 User peacenews OK. Password required
Password:
230 OK. Current restricted directory is /
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls
200-FXP transfer: from 123.63.112.168 to 10.215.10.80
200 PORT command successful

Please note that for the above machine, once I ran ls on ftp>, the prompt didn't come back.

On both the remote machines, I got different output when executed ls on ftp>

Answer 1

FTP is an ancient protocol. It relies on two TCP connections: a control connection over which commands are exchanged, and data connections for the content of files and also for the output of commands such as ls. What's happening here is that the control connection is established, but the data connections aren't going through.

By default (active mode), data connections are established from the sender to the receiver. For the output of ls, the data is sent by the server, so the server attempts to open a connection to the client. This worked well when FTP was invented, but nowadays, clients are often behind a firewall or NAT which may or may not support active FTP. Switch to passive mode, where the client always initiates the data connection.

Check the manual of your ftp command to see how to switch to passive mode by default. For a one-time thing, typing the command passive usually does the trick.

You may wish to switch to a nicer FTP client such as ncftp or lftp.

Answer 2

Full Complete solution for "ftp 500 Illegal PORT command". Click the following link: http://www.ucodice.com/articles/ftp-500-illegal-port-command/.

Excerpt

Trying to connect the ftp server & getting 500 Illegal port command. This issue may occur when ftp program is not configured for Passive mode.

You may get error snippet such as:

COMMAND:>              [3/11/2015 1:17:05 PM] PORT 192,168,0,101,196,215    
                       [3/11/2015 1:17:05 PM] 500 Illegal PORT command.    
ERROR:>                [3/11/2015 1:17:05 PM] Syntax error: command unrecognized.    
ERROR:>                [3/11/2015 1:17:05 PM] Failed to establish data socket.

To resolve this issue you can define the port or ftp in configuration file of ftp server & define the IP Address or PASV server.

Check the configuration file for below settings.

pasv_enable=YES
pasv_promiscuous=YES
pasv_max_port=Enter the max port range allowed on your server.
pasv_min_port=Enter the min port range allowed on your server.
pasv_address=Ip Address of your server.

After that restart the ftp service & check the ftp connection.