Great Circle Associates Firewalls
(December 1995)
 

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Subject: ftp & PASV
From: Alex Filacchione <alexf @ is . net>
Date: Thu, 7 Dec 1995 13:51:52 -0500 (EST)
To: firewalls @ greatcircle . com


On Fri, 1 Dec 1995, Sten Drescher wrote:

>  Well, the SOCKS ftp client uses (I think) the PASV command to
> tell the ftp server to use passive TCP ports for transfers.  That is,
> rather than the ftp server creating the connection to the client, it
> opens a port, tells the client what port to connect to, and waits for
> the client to create the connection.  This way, the connection is
> originating inside the SOCKS firewall, instead of outside it.
>
There are ftp clients/servers who do not understand the PASV command.
Anyone know how prevalent these are, and if this is something to be
worried about?  IOW, should I set up an ftp that issues the PASV command,
or should I use something like relay and have it sent to other ports, and
what problems would this cause?  Obviously the incoming ftp call would
have to come to the gateway or firewall running relay.  What are the
configuration issues w/ this?

Thanks,

Brain21

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