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Re: [v6ops] Practical question about MLD join for LL multicast

Mark Smith <markzzzsmith@gmail.com> Sat, 12 March 2016 22:47 UTC

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Date: Sun, 13 Mar 2016 09:47:42 +1100
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From: Mark Smith <markzzzsmith@gmail.com>
To: Ole Troan <otroan@employees.org>
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Cc: v6ops list <v6ops@ietf.org>
Subject: Re: [v6ops] Practical question about MLD join for LL multicast
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On 13 Mar 2016 4:24 AM, <otroan@employees.org> wrote:
>
> Sonum,
>
> > Have some questions from MLD Snooping switch point of view.
> >
> > If there are no Routers involved, it is Snooping switch responsibility
to send MLD Query to keep the groups alive on the switch.
> > What is the correct correct Source IP to use for General Queries ? Is
it Src IP all 0 or some link-local Address ? Which host stack would
like/accept what Source IP ? Have observed different observations with
different host stacks.
>
> see rfc4541.
>
> > Also, per discussion below - what is the right behavior for snooping
switch when it comes to link-local multicast groups - flood or snoop ? It
would be good to have a standard practice for this.
>
> it depends on the platform and how big forwarding table your switch can
handle.
> as far as I many switches flood,( and if you want my personal opinion, we
should change hosts so that they no longer send MLD joins for link-local
groups.)
>

And I think the people complaining about MLD for LL groups may then
complain when their hosts start receiving too many multicasts because
they're flooded.

I'd like to know more about these sorts of issues. What specific resource
is being exhausted in the switch? TCAM? How many hosts are attached to the
link - I'm wondering if, as a /64 effectively provides no limits at layer
3, people are now expecting to attach many more hosts to a link than they
would and have with IPv4.

Regards,
Mark.

> Best regards,
> Ole
>
>
>
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