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Date:      Wed, 26 Jun 2002 14:31:00 -0700
From:      Lars Eggert <larse@ISI.EDU>
To:        Matt Impett <M.Impett@flarion.com>
Cc:        "'freebsd-net@freebsd.org'" <freebsd-net@freebsd.org>, "'freebsd-questions@freebsd.org'" <freebsd-questions@freebsd.org>
Subject:   Re: source address based routing
Message-ID:  <3D1A3294.6010205@isi.edu>
References:  <8C92E23A3E87FB479988285F9E22BE46FDE778@ftmail.lab.flarion.com>

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Matt Impett wrote:
> gladly.. I am trying to implement reverse tunneling for mobile-IP.  The
> basic idea is that packets must be reverse tunneled to different IP
> addresses depending on the source address of the packet.  The reason the
> tunnel does not have an IP address associated with it is that I don't want
> to forward traffic down the tunnel for any other reason besides source
> addresses.  As soon as I assign the tunnel interface an address, traffic
> sent to that address will be tunneled.

Thanks, that was really helpful to get an idea of what your scenario is!

>>	route add DUMMY_NEXT_HOP -interface GIF
>>	ipfw add fwd DUMMY_NEXT_HOP all from SOURCE to any
> 
> 
> I have thought about doing this, but am a little concerned about assigning
> DUMMY_NEXT_HOP.  As soon as I issue "route add DUMMY_NEXT_HOP -interface
> GIF", that DUMMY_NEXT_HOP address is now unusable by anyone else.
> Therefore, I guess it would have to be private, but then this would stop
> anyone from actually using this private address in the local domain.

Well, nobody should be using a private address in any domain that's 
connected to the Internet, so you may be safe there.

If not, then you could do either

	(1) modify ipfw to allow specification of a local interface (as
	    opposed to a gatway IP adress) in the fwd rule
or
	(2) buy a large enough IP block so you can use your own
	    addresses for DUMMY_NEXT_HOP

> Plus,
> I don't know how many DUMMY_NEXT_HOPs to allocate, as I would need one for
> each tunnel I have set up, and the number of tunnels I set up is dependent
> on the number of mobile's that come into the system (which is somewhat of an
> unknown).

This makes (2) look infeasible, but (1) may still be an option.

Lars
-- 
Lars Eggert <larse@isi.edu>           USC Information Sciences Institute

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