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

Enno Rey <erey@ernw.de> Thu, 23 July 2015 12:27 UTC

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Date: Thu, 23 Jul 2015 14:27:10 +0200
From: Enno Rey <erey@ernw.de>
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Subject: Re: [v6ops] ref Hosts dont MLD to join LL groups
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Hi,

On Thu, Jul 23, 2015 at 02:16:43PM +0200, Alexandru Petrescu wrote:
> If one disallows all MLD joins for all link-scoped IP multicast 
> addresses - why does one need IP multicast addresses with link scope?
> 
> Why does one need the lino-layer  33::1 address?
> 
> If one doesnt need 33::1 then why Ethernet provides it?
> 
> I guess what I am trying to say is that it's useless to have multicast 
> groups if one can't join them.

define "join a multicast group"...

strictly speaking MLD as a whole is only needed for interdomain multicast anyway. on the local link you join a MC group by kind-of self declaration ("hey I consider myself part of that group so I'm interested in certain traffic and hence instruct my stack to listen to/process packets with certain addresses").
no need of MLD for that action. but "joining" on the local-link doesn't need MLD. 

best

Enno





> 
> Alex
> 
> Le 23/07/2015 13:51, Ole Troan a ??crit :
> > Alexandru,
> >
> > I???m afraid I couldn???t interpret your message. would someone else be able to translate?
> >
> > cheers,
> > Ole
> >
> >>>
> >>> 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
> >
> 
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