From owner-freebsd-net  Tue Jun 23 07:25:52 1998
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	Tue, 23 Jun 1998 07:25:43 -0700 (PDT)
Date: Tue, 23 Jun 1998 07:25:43 -0700 (PDT)
From: ken lindahl <lindahl@ack.berkeley.edu>
Message-Id: <199806231425.HAA27759@ack.berkeley.edu>
To: graeme.brown@bt-sys.bt.co.uk
Subject: RE: Looking for FreeBSD version of mrouted-3.8 (DVMRP)
Cc: freebsd-net@FreeBSD.ORG
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hi,

in most versions of IOS, ciscos do not maintain prune state when there
are DVMRP neighbors present on a multi-access LAN. (i don't know if this
description matches your instance, if not, please ignore my rantings.)

i think this is related to the poison-reverse mechanism used in DVMRP
to tell the upstream routers that there are downstream neighbors. ciscos
don't maintain the DVMRP poison-reverse information, therefore they are
not able to safely prune. (they may "cut off" downstream DVMRP neighbors
that they've "forgotten" about.) so, ciscos won't prune in the presence
of DVMRP neighbors on a multi-access LAN.

i think i've been told that this has been fixed in 11.2(13) and later,
also in 11.1CC(19) and later, though i haven't heard exactly how. i've
seen the problem; i've not yet tested 11.2(13) to see if it is fixed.
the one workaround that i know of is to tunnel between the cisco and
the DVMRP router (mrouted or bay router, for example), making sure that
the DVMRP router has disabled native (non-tunneled) multicast onto the
shared LAN.

ken lindahl
uc berkeley

On 23 Jun 1998 09:32:27, Graeme Brown <graeme.brown@bt-sys.bt.co.uk> wrote:
>Greg
>
>thanks for info. I tried mrouted-3.8.2 on a FreeBSD box interworking to a
>CISCO router running PIM-SM but could not get mrouted-3.8.2 to prune even
>though
>I explicitly put "pruning on" in /etc/mrouted.conf.
>
>Graeme

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