Subject: [manet] DLEP-17: well-known IPv4 link-local multicast address

From: RJ Atkinson <[email-masked]>
Date: Tue, 24 Nov 2015 10:33:04 -0500

At present, IANA Considerations only requests an IPv6 
link-local multicast address.

We will need one also to be defined for IPv4 for IPv4 deployments
of DLEP.  I have drafted precise IANA-compliant text below, so this
should be easy to insert into the DLEP draft.

Proposed New Text:

12.9  DLEP IPv4 Link-local Multicast Address

  Please allocate 1 multicast address to DLEP from the “IPv4 Multicast 
  Address, Local Network Control Block” registry for "DLEP Discovery Signals".

Yours,

Ran

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From: Rick Taylor <[email-masked]>
Date: Tue, 24 Nov 2015 16:12:34 +0000

Ran,

We resisted the urge to request one of the few remaining IPv4 multicast 
addresses, and went for the IPv4 broadcast address instead.  Discovery 
is a single-hop process anyway.

Cheers,

Rick

On 24/11/15 15:33, RJ Atkinson wrote:
> _______________________________________________
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From: RJ Atkinson <[email-masked]>
Date: Tue, 24 Nov 2015 13:05:45 -0500

> On 24  Nov 2015, at 11:12 , Rick Taylor <[email-masked]> wrote:
> 
> Ran,
> 

Thanks for the clarification.

(OPINION)

A) I don’t think that IPv4 link-local multicast addresses are particularly scarce.
   I checked that registry today before sending that note.

B) Use of broadcast seems impolite to other nodes on that link.  Modern
   IETF practice is to try to avoid using link-broadcast, in part because
   of widespread negative operational impacts of link-broadcast traffic.

Yours,

Ran

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From: Rick Taylor <[email-masked]>
Date: Wed, 25 Nov 2015 13:22:26 +0000

>     of widespread negative operational impacts of link-broadcast traffic.

We might have fallen into the trap of making assumptions about IANA 
here.  Personally I would prefer a link-local IPv4 multicast address.

Rick

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From: Henning Rogge <[email-masked]>
Date: Wed, 25 Nov 2015 14:40:23 +0100

> here.  Personally I would prefer a link-local IPv4 multicast address.

To be fair, RFC5498 (RFC5444 IANA allocation) got 224.0.0.109... that
doesn't look like we are running out of multicast addresses any time
soon.

Henning Rogge

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From: Rick Taylor <[email-masked]>
Date: Wed, 25 Nov 2015 13:46:15 +0000

> doesn't look like we are running out of multicast addresses any time

That's a good observation Henning.  Does anyone remember RFC5444 getting 
any negative feedback about the use of IPv4 link-local multicast?

Rick

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From: Henning Rogge <[email-masked]>
Date: Wed, 25 Nov 2015 14:55:29 +0100

> any negative feedback about the use of IPv4 link-local multicast?

Using real multicast addresses is a bit more tricky in C because the
"default API" is... ... ... lets say it is not straightforward to use.

But everything else is fine as far as I know.

Henning Rogge

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From: Henning Rogge <[email-masked]>
Date: Wed, 25 Nov 2015 16:28:20 +0100

On Wed, Nov 25, 2015 at 4:26 PM, Christopher Dearlove
<[email-masked]> wrote:
> Of course it wouldn't have been 5444 that got the feedback on an allocation, but 5498. But 5444 didn't get any feedback, and I'm reasonably sure 5498 didn't, though I wasn't an author of the latter.
>
> (What surprised me was that 5498 got an IP protocol allocation, one of only 256.)

Yes... the IP protocol allocation was a big surprise.

I think someone liked the idea of having a common protocol
format/framework for mesh networks.

Henning Rogge