Bob Rasmussen escreveu:

> In the FTP protocol, "passive" means that only one connection is
> established, originating in the client. All trafic goes over this
> connection. (In non-passive FTP, the server opens a second channel back to
> the client.)
>
> No such differentiation exists in SFTP. There is only one connection.
>
> The vendor may be using "passive" in a different sense, but I don't think
> it is a widely accepted usage.


in really, both passive and active ftp modes uses two connections. The
first, which is originated on client (to port 21 on server), is the
control connection, for authentication, command/response exchanges, etc.
The second connection, which transfer effective data, support two modes:
passive: originated from client to server. Uses destination port
defined on control connection.
active: originated from server to client. Uses destination port 20 on
client.

See http://www.faqs.org/rfcs/rfc1579.html (Firewall-Friendly FTP).

good resources:
http://en.wikipedia.org/wiki/File_Transfer_Protocol
http://www.slacksite.com/other/ftp.html
http://www.faqs.org/rfcs/rfc959.html (for the braves!)


Tom Lobato
www.tinecon.com.br