RE: Active vs passive FTP

[Tim McCarthy <TimM@xxxxxxxxxxxxxxxxxx>]

No. FTP data connections are established EVERY time "data" needs to flow
- that includes PUTs, GETs, LiSts and DIRectories. In active mode the
client issues a PORT command specifying a port number for the server to
establish the data link with. This does NOT have to be port 20 - even
for PC's it will depend on the FTP client software. In passive mode the
client asks the server to pick a port. The server responds with the port
number and the client then connects to that port. You will probably find
that with each new data connection established a new port number is
selected and "old" connections linger in NETSTAT.
  

TrailBlazer Systems, Inc.
http://www.softwarejungle.com
AS/400 E-Commerce Solutions

Chaos, panic, & disorder - my work here is done.

> -----Original Message-----
> From: SIMS, KEN [SMTP:KSIMS@SOUTHERNWINE.com]
> Sent: Monday, November 29, 1999 4:57 PM
> To:   MIDRANGE-L@midrange.com
> Subject:      RE: Active vs passive FTP
> 
> Hi Jim -
> 
> >Date: Mon, 29 Nov 1999 16:17:39 -0800
> >From: Jim Langston <jlangston@conexfreight.com>
> >Subject: Re: Ethernet x-over cable
> >
> >Hmm?  Please explain the difference between active
> >and passive modes of FTP.  I wrote an FTP client a few
> >years back on a PC in Delphi just to do it.  I got it working,
> >then abandoned it, I just wanted to see how it was done.
> 
> I'll jump in here since I had to deal with this recently for a
> firewall on
> my PC at home.  As I understand, active vs passive only applies on
> gets,
> basically just file gets and directory lists.
> 
> In both cases, the client sends the request to the server on port 21.
> 
> In active mode, the server then initiates a data connection to the
> client to
> send the actual file data or directory listing.  This is done on a
> port of
> 1024 or higher.  If there is a firewall set to reject connections
> initiated
> by the other end, this is a problem.
> 
> In passive mode, the client initiates the data connection to the
> server.
> This is done on port 20.
> 
> For file puts, the client always initiates the data connection.
> 
> Ken
> Southern Wine and Spirits of Nevada, Inc.
> Opinions expressed do not represent those of my employer or anyone
> else.
> 
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