[AccessD] FTP command line, passive mode

On 29 Oct 2004 at 20:28, Steve Conklin (Developer at Ultr wrote:

> Thanks, Stuart.
> I have only used FTP command line to login/upload/download, so I don't
> know all of its intricacies.  But according to what I read further on
> RFC 959, wouldn't an "Active" session need to be initiated first, then,
> to issue the PASV command? ... I ask this in pursuit of the answer to
> the  original question (which wasn't mine, but an interesting topic!)
> 

There are two connections involved in a FTP session, control and data.

A control connection is established first on the standard control port and 
then a data connection is established.   The active/passive differentiation 
is in the way the port for the data connection is selected.

In an active session, the client connecting to the server specifies what 
port is to be used for the data connection (either the default or a user 
specified port using the PORT command).

Using PASV to establish the data connection tells the FTP Server to pick an 
available port and tell you to listen on it.  This is necessary when you 
are talking to a busy FTP server with lots of simulatneous connections - 
only the server knows what ports it has available at the time.

-- 
Stuart