Subject: (IPng 7583) Re: Multicast Listener Discovery timing question

From: Jean-Luc Richier <[email-masked]>
Date: Wed, 2 Jun 1999 20:04:08 +0200 (MET DST)

Dans votre courrier du 2 Jun 10:25 vous ecrivez :
>> As I said in a previous mail, I suppose the rationale for using MLD
>> on sollicited node multicast groups is that even though 
>> multicast addresses
>> whose scope is 2 should not be routed, there can be level 2 
>> bridges/switches
>> which are performing multicast selective forwarding, and thus 
>> engage in the
>> mld protocol.
>
>Gosh, I thought that MLD should *not* be used for link-local multicast
>addresses. Our implementation does not send MLD messages when it joins
>solicited-node multicast groups.
>

Is my hypothese on the reason for doing MLD for link scope multicast correct?
Is there an other reason for the following draft text ?

    MLD messages ARE sent for multicast addresses whose scope is 2 (link-
    local), including Solicited-Node multicast addresses [ADDR-ARCH], except
    for the link-scope, all-nodes address (FF02::1).

What is the behaviour for a router if it receives a multicast with scope = 2?
Always drop it, or forward it in some cases? and if so, what case(s)?

-- 
Jean-Luc RICHIER ([email-masked]  [email-masked])
Laboratoire Logiciels, Systemes et Reseaux (LSR-IMAG)
IMAG-CAMPUS, BP 72, F-38402 St Martin d'Heres Cedex
Tel : +33 4 76 82 72 32 Fax : +33 4 76 82 72 87
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From: Steve Deering <[email-masked]>
Date: Wed, 2 Jun 1999 12:18:29 -0700

>Always drop it, or forward it in some cases? and if so, what case(s)?

If the router is itself a listener to the destination multicast address,
it passes it to the appropriate upper-layer protocol(s) on the router;
otherwise, it drops it.  It never forwards it.

If an upper-layer protocol on the router itself originates a multicast
packet with link-local scope, the router transmits that packet on the
appropriate link.

Steve