Subject: Status of subnet-local multicast?

From: Kerry Lynn <[email-masked]>
Date: Wed, 27 Jun 2012 13:13:05 -0400

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?

Thanks, -K-

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From: Stig Venaas <[email-masked]>
Date: Wed, 27 Jun 2012 10:53:00 -0700

On 6/27/2012 10:13 AM, Kerry Lynn wrote:
> 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...

Stig

>
> Thanks, -K-
>
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From: Kerry Lynn <[email-masked]>
Date: Wed, 27 Jun 2012 14:47:10 -0400

On Wed, Jun 27, 2012 at 1:53 PM, Stig Venaas <[email-masked]> wrote:

>> http://tools.ietf.org/html/**draft-lynn-homenet-site-mdns<http://tools.ietf.org/html/draft-lynn-homenet-site-mdns>
> 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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From: Ralph Droms <[email-masked]>
Date: Wed, 27 Jun 2012 16:11:52 -0400

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