Subject: multicast routers on switches with IGMP snooping

From: Patrick De Muynck <[email-masked]>
Date: Tue, 02 Jun 1998 15:09:27 +0200

In my understanding, a LAN-attached multicast router must be able to
receive all IP multicast packets that are transported over that LAN
(otherwise I must be missing something IP multicast routing).

So what about switches that do IGMP snooping?  Since I know of no IGMP
membership report 'for all groups', I suppose that one has to
explicitly indicate to the switch which port(s) have multicast routers
attached.

Is this correct?  How would you do that for the newer 3COM switches
(3300 model)?

Regards,

Patrick De Muynck

BELNET, the Belgian National Research Network

[email-masked]  |	DWTC - BELNET
Tel : +32/2/238.36.76	    |	Wetenschapsstraat, 4
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From: Bill Fenner <[email-masked]>
Date: Tue, 2 Jun 1998 08:10:09 PDT

In message <[email-masked]>you write:
>Since I know of no IGMP

It's possible for the switches to snoop on multicast routing protocols;
any box that is sending multicast routing protocol packets (e.g. DVMRP,
PIM, ...) is probably a router.  But yes, failing that, all of the
multicast router ports have to be configured.

  Bill

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From: Cyndi Jung <[email-masked]>
Date: Tue, 02 Jun 1998 08:07:22 -0700

The switches can figure out which ports have routers attached. 
They then send all multicast packets to those ports.  There
is no configuration required to tell the switches where the
routers attach.

Cyndi