Subject: FreeBSD Mbone "terminal"

From: Mark Handley <[email-masked]>
Date: Mon, 13 Apr 1998 11:57:03 -0400

[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

---

From: Steve Deering <[email-masked]>
Date: Mon, 13 Apr 1998 12:52:06 -0700

> #discard interface for multicast packets

Don't you also have to assign a legal, global address and subnet mask to
the discard interface, so there's an address to put in the source field
of multicast packets orginating there, and a subnet number (perhaps a /32)
for mrouted to advertise?

Steve

---

From: Mark Handley <[email-masked]>
Date: Mon, 13 Apr 1998 17:00:31 -0400

>for mrouted to advertise?

Yes, you do need to do this.  I originally advertised a net-10 address
(for testing) but this is a bad idea for production as some people
rightly filter it, so now I've got a real /30 subnet address.

Mark

---

From: Luigi Rizzo <[email-masked]>
Date: Mon, 13 Apr 1998 21:24:16 +0200 (MET DST)

> for mrouted to advertise?

good point... i was just asking mark if a source on a 10.X.Y.Z subnet
was visible from the outside, since I and possibly others use such
addresses for experiments.

	cheers
	luigi
-----------------------------+--------------------------------------
Luigi Rizzo                  |  Dip. di Ingegneria dell'Informazione
email: [email-masked]    |  Universita' di Pisa
tel: +39-50-568533           |  via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522           |  http://www.iet.unipi.it/~luigi/
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