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Date:      Sat, 19 Feb 2000 19:43:43 -0700 (MST)
From:      Charles Mott <cmott@scientech.com>
To:        freebsd-questions@freebsd.org
Subject:   Re: Redirecting/mapping ports to a local machine... help!
Message-ID:  <Pine.LNX.4.10.10002191935400.29722-100000@if.scientech.com>
In-Reply-To: <20000219213848.H60348@cc942873-a.ewndsr1.nj.home.com>

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> > Many people use ftp in non-passive mode from behind natd
> > without any problems.
> 
> Many people get lucky then. From the alias_ftp.c source,
> 
>     For this routine to work, the PORT command must fit entirely
>     into a single TCP packet.  This is typically the case, but exceptions
>     can easily be envisioned under the actual specifications.

I wrote the alias_ftp.c source code and the comment that
you cite.  It is unusual to see a PORT command divided into
more than one packet.  There is a firewall toolkit that
deliberately does this, but I know of no other examples.

> 
> > > Use of a control channel and a data channel is a basic part of the ftp
> > > protocol. See RFC 959. Unimplemented RFC 2428 might be interesting too.
> 
> But we need to point out that the this special handling of FTP by NAT
> is for _clients_ behind the NAT box only, not servers.
> -- 
> Crist J. Clark                           cjclark@home.com
> 



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