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Date:      Tue, 14 Sep 1999 11:34:06 -0700 (PDT)
From:      Julian Elischer <julian@whistle.com>
To:        Andre Chang <Andre@HighCaliber.com>
Cc:        freebsd-ipfw@FreeBSD.ORG
Subject:   Re: IPFW configuration as a transparent proxy
Message-ID:  <Pine.BSF.3.95.990914111804.1204D-100000@current1.whistle.com>
In-Reply-To: <021401befedd$27a14320$1ad2d9ce@work.highcaliber.com>

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The fwd option forces a packet to be sent to:

 1/ a nominated local socket
or
 2/ out a nominated interface tot a nominated 2nd machine.

However it doesn't change the packet in any way..  this means that in case
(2) above, the second machine will not accept the packet unless it also
has a 'fwd' rule to make it do soi( as in case 1).  If this is not the
case, it will examine the packet and send it towards it's original
destination. 

In the first case, This basically allows transparent proxy, by redirecting
all outgoing requests to port 80 (that are not starting at the local
machine) (i.e. requests coming in on the local interface  that would
normally be routed out your WAN interface) to be redirected to whatever
port your proxy is listenning on.

e.g. 
ipfw add 2 fwd 127.0.0.1,3137 tcp from any to any 80 out recv ed1 xmit ng0

This redirects any packets that are about to go out through ng0 (our LAN
frame relay link), that originated on the LAN (ed1).The reson for being so
specific is that we don't want to capture the requests that the proxy
makes!

hope this helps!

julian



 



On Tue, 14 Sep 1999, Andre Chang wrote:

> Hello,
> 
> I would like to know if this is the place to ask about configuring IPFW to
> serve
> as a transparent proxy by use of the IPFW's "fwd" option.
> 
> Is there anyone who has used this option toward this goal or something
> similar?
> Any response on this topic would be greatly appreciated. Thank You.
> 
>  -- Andre Chang
> Network Engineer.
> High Caliber Systems, Inc.
> 
> 
> 
> 
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