Re: [v6ops] ref Hosts dont MLD to join LL groups

Alexandru Petrescu <alexandru.petrescu@gmail.com> Thu, 23 July 2015 11:43 UTC

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To: Ole Troan <otroan@employees.org>
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From: Alexandru Petrescu <alexandru.petrescu@gmail.com>
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Subject: Re: [v6ops] ref Hosts dont MLD to join LL groups
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Le 22/07/2015 14:27, Ole Troan a écrit :
>> Regarding the mic discussion about unicast RAs a SHOULD.
>>
>> I have been directed that the reference saying that Hosts dont MLD
>> to join multicast groups is RFC3810:
>>
>> "  The link-scope all-nodes multicast address, (FF02::1), is
>> handled as a special case.  On all nodes -- that is all hosts and
>> routers, including multicast routers -- listening to packets
>> destined to the all-nodes multicast address, from all sources, is
>> permanently enabled on all interfaces on which multicast listening
>> is supported.  No MLD messages are ever sent regarding neither the
>> link-scope all-nodes multicast address, nor any multicast address
>> of scope 0 (reserved) or 1 (node-local).”
>
> I do wonder if we should expand that exception to all link-scope
> multicast addresses.
>

I would beg to disagree.

If we expand that to all link-scoped groups, may lead to dismantling 
IPv6 dependence on 33::1 - ff:ff:ff:ff:ff would be sufficient.

My oppinion would rather be to modify the MLD RFC to mandate MLD joins 
for all scopes.

Ethernet has primitives for joining the corresponding link-layer groups, 
and in some cases they are used. Maybe all should use them.

> the bridge implementors I speak to tell me that they don’t have
> enough state to do MLD snooping for link-local scoped multicast
> addresses anyway...

This may be dumb from my side, but why dont bridge implementers use 
link-layer multicast?  They shouldnt implement MLD, and not snoop it. 
The Hosts should send the necessary link-layer multicast joins 
(triggered by themselves sending MLD REPORT for these groups) to the 
bridge addresses.

Alex

> cheers, Ole
>