From owner-freebsd-multimedia  Mon Apr 13 08:57:13 1998
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From: Mark Handley <mjh@east.isi.edu>
X-Organisation: Information Sciences Institute, USC
X-Phone: +1 617 253 6011
To: mbone@isi.edu
cc: freebsd-multimedia@FreeBSD.ORG
Subject: FreeBSD Mbone "terminal"
Date: Mon, 13 Apr 1998 11:57:03 -0400
Message-ID: <14827.892483023@north.lcs.mit.edu>
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[I think this solution might be useful for others, hence mailing the
list]

I have an Mbone machine using a cable modem as my access link, but
anyone using ISDN/PPP might have the same requirement - to have an
Mbone tunnel, but not to source native multicast onto any interface.
In my case it's because I don't want to pump multicast packets into my
cable modem, but in the ISDN case it may be because you don't have a
multicast capable interface at all.

In any event, the solution I've ended up with is to configure a
multicast capable FreeBSD "discard" interface, and to set the route
for 224/4 to point there.

To do this you need to patch if_disc.c to not set IFF_LOOPBACK.  
I.e., change:
        ifp->if_flags = IFF_LOOPBACK | IFF_MULTICAST;
to
        ifp->if_flags = IFF_MULTICAST | IFF_BROADCAST;

and then build the kernel with:
#discard interface for multicast packets
pseudo-device   disc    1

Now I have a machine that runs mrouted happily, and sends and receives
via the tunnel on its physical interface, but that never sends native
multicast packets anywhere.

Thanks to Bill Fenner and Garrett Wollman for helping me figure this
out!

Cheers,
	Mark


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