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Date:      Mon, 19 Aug 2002 10:39:54 -0700
From:      Lars Eggert <larse@ISI.EDU>
To:        Luigi Rizzo <rizzo@icir.org>
Cc:        net@FreeBSD.ORG
Subject:   Re: Bridging when one interface has no carrier
Message-ID:  <3D612D6A.9020604@isi.edu>
References:  <3D61224B.2020902@isi.edu> <20020819102951.A38869@iguana.icir.org>
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[-- Attachment #1 --]
Luigi Rizzo wrote:
> I guess the responsible of the problem is this part of code
> in sys/net/if_ethersubr.c:ether_demux():
> 
>         /* Discard packet if interface is not up */
>         if ((ifp->if_flags & IFF_UP) == 0) {
>                 m_freem(m);
>                 return;
>         }
> 
> which is somewhat funny, because once we have the packet, we
> might as well process it.
> 
> Now, one could bypass the test for the bridging case,
> or remove it altogether... I am not sure which one is
> the best approach.

I like the first idea (bypass when bridging) better. Link layers usually 
follow the "strong host model" (see RFC 1122), where inbound packets are 
dropped unless they match the destination address of the inbound 
interface. (Compared to the "weak host model" of IP, which acceptes 
inbound packets when their destination address matches *any* local 
interface.) Disabling that test altogether might weaken that property?

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

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