Re: [v6ops] Interesting problems with using IPv6

Brian E Carpenter <brian.e.carpenter@gmail.com> Wed, 10 September 2014 02:16 UTC

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Date: Wed, 10 Sep 2014 14:16:15 +1200
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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To: Fernando Gont <fgont@si6networks.com>
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Subject: Re: [v6ops] Interesting problems with using IPv6
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On 10/09/2014 12:47, Fernando Gont wrote:
> On 09/09/2014 05:40 PM, Brian E Carpenter wrote:
>>>> Then, let me change the question: Why do I need MLD for *this*?
>> I think Brian Haberman's reply shows why that is the wrong question.
>> You need MLD for every multicast group, including a solicited-node
>> group, and if you insist on MLD snooping in the bridges (let's not
>> obfuscate by calling them switches) then you need to snoop every
>> solicited-node group.
>>
>> My question is orthogonal to MLD snooping: why do we require router-alert
>> for MLD messages referring to a solicited-node group, since it by
>> definition is limited to a single L2 link (even if that link is
>> split up by bridges)?
> 
> .. to avoid them being a special case?  -- i.e., all MLD packets carry a
> Router Alert option. 

Yes, it would be an exception. But we know that HbH options in general
and Router Alert in particular are a serious performance issue, and
that all links carry this particular kind of MLD traffic, so an
exception seems like something to be discussed.

> And, actually, an MLD report could potentially
> include groups other than solicited-node (so you probably wouldn't want
> to turn the "include a router-alert" on and off).

Sure, the exception would have to be for messages containing only
solicited-nodes data.

   Brian