Re: [v6ops] Interesting problems with using IPv6

Erik Nordmark <nordmark@acm.org> Fri, 12 September 2014 15:49 UTC

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Date: Fri, 12 Sep 2014 08:49:15 -0700
From: Erik Nordmark <nordmark@acm.org>
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To: Brian E Carpenter <brian.e.carpenter@gmail.com>, Fernando Gont <fernando@gont.com.ar>
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Cc: IPv6 Operations <v6ops@ietf.org>, l.wood@surrey.ac.uk
Subject: Re: [v6ops] Interesting problems with using IPv6
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On 9/9/14, 12:20 AM, Brian E Carpenter wrote:
> On 09/09/2014 16:10, Fernando Gont wrote:
>> On 09/08/2014 06:59 PM, Brian E Carpenter wrote:
>>>> See: draft-pashby-magma-simplify-mld-snooping-01
>>> OK, but I would also like to understand why we require
>>> MLD messages for a Solicited-Node multicast address to
>>> set Router Alert.
>> Because in theory the multicast router needs to process the MLD message
>> to build its forwarding table....
> Why, for the Solicited-Node group, which is only meaningful on the link
> from which the MLD message arrives?

Correct. That is true for all the link-local groups. The only reason to 
report link-local groups is to enable MLD snooping switches. Routers 
should only care about groups scope > link-local. Thus we can remove 
router-alert from MLD reports for link-local groups.

Another sub-optimal aspect is that when a router sends a MLD query, it 
gets responses for all groups including link-ocal. Only an MLD query 
from a snooping switch would need to elicit responses for link-local 
groups. (That would imply adding some flag to the MLD query which might 
not be worth-while at this point in time.)

    Erik

>
> (NBMA is different of course, but that is not the scenario in the blog.)
>
>    -- or are you arguing that since the
>> Dst Addr "includes" the router, the router should process the MLD
>> message anyway?
> In its role as a node on the same link, participating in ND on that
> link, yes. In its role as a forwarding device, surely it should ignore
> traffic to the Solicited-Node address? So Router Alert is not
> needed. Or am I missing something?
>
>      Brian
>
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