Re: FTP Port Problems

[Scott Klement <klemscot@xxxxxxxxxxxx>]

Just a note to explain how FTP works:

Port 21 is used for the "control connection" (where commands, like cd,
put, get, ls, etc are sent to & from the server)

When one of those commands calls for data to be transferred, it opens up a
second connection.

In "passive" mode, the server picks an available port (it can pick any
number) and then tells the client to connect to it.
In "standard" (non-passive) mode, the client picks an available port, and
tells the server to connect back to the client.
In either case, this negotiated connection is used just to transfer the
data (the contents of a file, or directory info) and then it's closed.

The problem with the FTP protocol is that it can pick ANY port, so it's
hard to make it work thru a firewall.

Here's a few tips:

    1) If your client is allowed to make outgoing connections on any port,
         and only incoming connections are restricted, then use passive
         mode.   (This is very common at companies with an intranet)

    2) If the FTP server has the firewall, and it's allowed to make
         outgoing connections on any port, but incoming is restricted
         to port 21, then use standard mode (non-passive).

    3) If your LAN is set up to strictly only allow certain ports in
         both directions, you may need to set up an FTP proxy so that
         you can bypass the firewall.

    4) Some of the better FTP clients are able to work through an
         HTTP proxy, as well, so that might also be an option.

Hope that helps...


On Mon, 24 Jun 2002 justin@reliatek.com wrote:

> Hi Everyone,
>      I am having problems trying to FTP into my AS400. I have ports 20,21
> passed to it. I can log in, change directories, but when I do a put command
> I get this....No response received from the FTP Server.
> No response from the host; all connections closed.
> Unable to setup for an active data connection to the server, reason code 2.
>
> Is there another port I have to pass????Please Help
>
> Justin Houchin
> Programmer and Web Developer
> ReliaTek, Inc
> justin@reliatek.com
>
>