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Date: Mon, 25 Apr 2011 13:53:13 +0200
From: Lionel Fourquaux <lionel.fourquaux@normalesup.org>
To: Robert Bonomi <bonomi@mail.r-bonomi.com>
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Cc: 
Subject: Re: routing to a directly attached subnet without an address in
 this subnet
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On Sun, Apr 24, 2011 at 06:43:11PM -0500, Robert Bonomi wrote:
>Sorry, it _is_ impossible.

:(

>simply put, to communicate _on_ a network, you have to be *ON* that
>network, i.e., 'have an address in that network's address-space'.

I don't quite see why this would be required, as long as packets are 
routed as they should.

>It is perfectly legitimate for two (or more) separate networks to share
>the same physical media.

Yes.

>*ONLY* the address of the device distinguishes which network the trafic
>goes to/from.

But this is the destination address on packets. The point here is, why 
would the router need an address that is never used as source or 
destination?

>> I can't see any strong reason for requiring that em1 have
>> an address for every directly attached subnet packets are routed
>> to.
>
>Think about how 'reply' packets have to be routed by other machines
>on that subnet.

Packets from other machines are routed to fe80::1234:56ff:fe78:9abd 
(link local address of the router), so this part is fine.

Thanks!