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Date:      Fri, 07 May 1999 10:45:05 +0200
From:      Thierry Herbelot <Thierry.Herbelot@alcatel.fr>
To:        questions <questions@freebsd.org>
Subject:   Passive FTP with natd ?
Message-ID:  <3732A811.7F51584B@telspace.alcatel.fr>

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Hello,

I've set up a small home network with two 3.1-Stable machines, one being
the gateway to the Internet via a TV cable connection (ethernet
connection to the cable modeme and DHCP negociation for the external IP
address - the two machines were CVSupped and "make world"-ed during this
week).

This seteup works quite well (and with very little load on the gateway -
I'm even contemplating changing the gateway : I've got an oldish 386sx
which is presently idle).

But one thing is still annoying : I must use a passive connection with
FTP when I connect from the internal machine to an outside server (case
in point : I was trying to download RedHat 6.0 from cdrom.com).

When I read the lialias(3) man page, it seems that the aliasing code can
cope with ftp transfers and modifies on-the-fly FTP packets so that you
don't have to use the "passive" option (this is essentially intyeresting
for graphical ftp clients where it is not obvious to know how to switch
to passive mode).

	Thus : is it possible to setup natd so as to modify FTP packets ?
	(is there a specific rule to insert into rc.firewall ?)

	TIA

	TfH

PS : extract from libalias(3)

 int PacketAliasOut(char *buffer, int maxpacketsize)
 
 An outgoing packet coming from the local network to a remote machine is
 aliased by this function.  The IP packet is pointed to by buffer r, and
 maxpacketsize indicates the maximum packet size permissible should the
 packet length be changed.  IP encoding protocols place address and port
 information in the encapsulated data stream which have to be modified
and
 can account for changes in packet length.  Well known examples of such
 protocols are FTP and IRC DCC.


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