Mailinglist Archive: opensuse-security (471 mails)

[anyware@xxxxxxxxxxx]

On Mon, Oct 09, 2000 at 09:34:23AM +0200, Philipp Snizek wrote:
> Hello
> 
> Please can somebody tell me the difference between active ftp and passive
> ftp?
> 
> thank you
> Philipp


If you do some ftp then you have a server somewhere in the world and a
client program on your system.
The servers runs day after day and waits for connections, he 'listens'
on a port (usually port 21). The client connects to that port and then
the client sends commands, and the server responses if you are lucky.

To transfer data (after a get or put command perhaps) they do NOT use
this existing connection, they open another one instead. But which of
both plays the the server (listening) and which plays the client
(connecting) to establisg this second channel?

- If the client chooses the 'passive' mode, then he sends a PASV command
  to the server. The server opens a port for the data connection
  (usually port 20 I believe) and sends an answer to the client
  containing the host adresse.
  The client connects to this adress/port combination.

- If the client chooses the 'active' mode, then he creates the
  listening side of the connection, sends his adress to the server,
  and the server connects.

Since in passive mode the server sends an adress it is able to let the
client connect to any other server (gateway) by sending the
appropriate adress.


Klaus

-- 

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       Klaus Wachtler
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       Tel. +49-5191-70271, +49-171-4553039
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       email AnyWare@xxxxxxxxxxx
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