Subject: RFC2461bis: Multicast capable vs Multicast Service [was RE: Comme nts for rc2461bis]

From: "Elwyn Davies" <[email-masked]>
Date: Tue, 26 Oct 2004 10:39:59 +0200

Hi.

Using the term 'multicast services' around this area is confusing.  If the
link MUST provide multicast services maybe that is something that should be
in the basic definition of IPv6 (it isn't stated explicitly in RFC2460)
rather than in 2461bis.

Expanding on what I said originally, one reasonable interpretation of the
requirement that all links support multicast services is that they are in
some sense 'multicast capable': if you take this view then *all* links are
necessarily multicast capable.

So I think the problem is that the language doesn't properly convey what I
think is the intention: I believe we are trying to distinguish between:
- links that provide multicast *as a Layer 2 capability* ('The hardware does
multicast')
- links that don't, so that the multicast services have to be provided as an
overlay

Hope this clarifies my point.

Regards,
Elwyn

Original Message
================
S2.2 and S3: 
The note after the NBMA definition says that '...all link types (including
NBMA) are expected to provide multicast service for IP...'.

A naive interpretation of the phrase in S3 'On multicast-capable links...'
(just after the Redirect bullet) in conjunction with the previous note might
take it that actually all links are multicast-capable.  The term should be
explicitly defined so as to explicitly exclude NBMA and any other sort of
links that this phrase is not supposed to apply to - or to allow it to be
done optionally on this sort of link - the current wordings are too vague.
This is also related to the comment on 6.2.1 below. 

=> I'm not sure I see the problem you see (and I looked at the 2462 thread).
We can make the 

link definition for multicast, a definition for "multicast capable". But
apart from that the current

spec states refers to other docs in the introduction when it discusses NBMA
links.

The text you refer to above is talking about multicast services, which is a
different issue.

So for now, I'll s/multicast/multicast capable in 2.2 and that should do the
job IMO.

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Elwyn B Davies

        Routing and Addressing Strategy Prime & IPv6 Core Team Leader
        CTO Office, Portfolio Integration		Solutions Ready

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