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RE: RFC2461bis: Multicast capable vs Multicast Service [was RE: Comments for rc2461bis]

Title: RFC2461bis: Multicast capable vs Multicast Service [was RE: Comments for rc2461bis]
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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  

=> Exactly.  I guess our difference is that I get the distinction from the spec when

I read it now (with "multicsat capable" replacing "multicsat" in 2.2). Is that a sufficient

change ? Let me know if you think another change is needed.



Hope this clarifies my point.


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.


Elwyn B Davies

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