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Date:      12 Apr 2001 16:57:46 -0500
From:      Kirk Strauser <kirk@strauser.com>
To:        freebsd-ipfw@freebsd.org
Subject:   Re: Beating a dead horse - ipfw and FTP
Message-ID:  <87bsq1hjc5.fsf@pooh.honeypot>
In-Reply-To: <200104121916.VAA74511@info.iet.unipi.it>
References:  <200104121916.VAA74511@info.iet.unipi.it>

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At 2001-04-12T19:16:23Z, Luigi Rizzo <luigi@info.iet.unipi.it> writes:

> we have stateful ipfw and passive ftp -- the combination of the two should
> give you the protection that you want.  Am i wrong ?

Unfortunately, yes.  The annoying part is that there is no way to tell what
port the FTP server will want you to connect to ahead of time:

  1.  Connect from client to server port 21
  2.  Ask the server what port to connect to for data transmission
  3.  Connect from client port 20 to the specified port on the server

The old style was even worse:

  1.  Connect from client to server port 21
  2.  Connect from server to client port 20

So, there's no way to know what port to open (for step 3 of the first
listing) in advance.
-- 
Kirk Strauser

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