Re: [v6ops] v6ops Digest, Vol 52, Issue 41

[Mark ZZZ Smith <[e-mail]>]

----- Original Message -----
> From: Gert Doering <[e-mail]>
> To: Mark ZZZ Smith <[e-mail]>
> Cc: Gert Doering <[e-mail]>; Tariq Saraj <[e-mail]>; "[e-mail]" <[e-mail]>
> Sent: Friday, 19 December 2014, 22:38
> Subject: Re: [v6ops] v6ops Digest, Vol 52, Issue 41
> 
> Hi,
> 
> On Thu, Dec 18, 2014 at 10:03:32PM +0000, Mark ZZZ Smith wrote:
>>  > There is no wide-area multicast anyway.
>> 
>>  Technically it should be universal, as DAD uses multicast and DAD is 
> mandatory (except for anycast addresses), which should include tunnels.
> 
> This is not *wide-area* multicast, but link-local.
> 
> Slight difference.
> 

Perhaps I'm misunderstanding what you're saying, however 6to4 creates a single NBMA link. As per the RFC4861 text I referenced, NBMA links should emulate a multicast capability. An Internet search found the following draft that seems to specify how multicast was to be emulated over 6to4:

"Support for Multicast over 6to4 Networks"
https://tools.ietf.org/html/draft-thaler-ngtrans-6to4-multicast-01



There seems to be a fairly common belief that the ability to IPv6 multicast across a link is optional, because I think in IPv4 it was.

It seems to me that the IPv6 approach is that the minimum characteristics IPv6 expects of links is to be able to unicast and multicast across them. If a link doesn't support multicast then multicast capability is expected to be emulated below or within the lower part of the IPv6 layer - which is what the text I quoted from RFC4861 says about emulating multicast on point-to-point and NBMA links.

I think the advantage of the IPv6 approach is that there doesn't have to be link capability specific handling with IPv6 itself - all links appear to have the same set of unicast and multicast capabilities. Consequently, any of the standard IPv6 mechanisms, such as Neighbor Discovery DAD or Neighbor Discovery Address Resolution, should work and work the same way over all link types, rather than being different depending on whether the link natively supports multicast or not. Applications that use multicast of any scope should also just work regardless of the underlying link type. So, for example, Multicast DNS, using link-local multicasts, should work over 6to4 NBMA links as seamlessly as it does over 802.3 or 802.11 links.


Regards,
Mark.


> 
> Gert Doering
>         -- NetMaster
> -- 
> have you enabled IPv6 on something today...?
> 
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