Re: Status of subnet-local multicast?

[Ralph Droms <[e-mail]>]

Dave Thaler and I are exchanging e-mail about this very topic.

According to Dave, scope 3 was assigned for subnet-scoped multicast, to accommodate multi-link subnets.  Then the IPng WG decided multi-link subnets is a bad idea and Dave wrote RFC 4903.  One of the side-effects was to relabel scope 3 as 'reserved'.

Now, however, me have multi-link subnets in the 6lowpan/RPL architecture, picked up by ZigBee IP.  Might be time to relabel scope 3 back to subnet-scope.

- Ralph

On Jun 27, 2012, at 2:47 PM 6/27/12, Kerry Lynn wrote:

> On Wed, Jun 27, 2012 at 1:53 PM, Stig Venaas <[e-mail]> wrote:
> On 6/27/2012 10:13 AM, Kerry Lynn wrote:
> Greetings,
> 
> RFC 3484 section 3.1 defines "subnet-local (0x03)" multicast scope, but
> later RFC 4291 section 2.7 defines this multicast scope value as reserved.
> Can I ask if the later interpretation is the correct one?
> 
> I ask in the context of e.g.
> http://tools.ietf.org/html/draft-lynn-homenet-site-mdns
> where we need a scope greater than link-local in order to span a 6LoWPAN
> subnet, but less than site-local in order to reserve the property "Each
> interface
> belongs to exactly one zone of each possible scope." for future site-local
> protocols that might include the 6LoWPAN router port.
> 
> Should I select admin-local scope, or is subnet-local scope available
> for use?
> 
> I've always been a bit curious why it got marked as reserved. It was
> (unassigned) in RFC 2373, but reserved in RFC 3513. I don't remember
> any discussion on this.
> 
> It seems 4 admin-local would be appropriate then. Unless perhaps if 3
> is somehow reserved to allow for maybe future use like this...
> 
> Perhaps it was originally discussed as an analog to IPv4 subnet broadcast,
> but that usage was later thought unnecessary.  Hopefully an IPv6 historian
> will chime in...
> 
> Thanks, -K-
> 
> Stig
> 
> 
> Thanks, -K-
> 
> 
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