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Re: [v6ops] question about draft-jjmb-v6ops-unique-ipv6-prefix-per-host

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 04 July 2017 20:17 UTC

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To: Ole Troan <otroan@employees.org>
Cc: Ted Lemon <mellon@fugue.com>, v6ops@ietf.org
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From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Wed, 05 Jul 2017 08:17:32 +1200
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Subject: Re: [v6ops] question about draft-jjmb-v6ops-unique-ipv6-prefix-per-host
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On 04/07/2017 18:59, Ole Troan wrote:
> Brian,
> 
>>> On Jul 3, 2017, at 5:41 PM, Ole Troan <otroan@employees.org> wrote:
>>>> It breaks the assumption that everything you want discovered is within the same broadcast domain. Many think that assumption was broken anyway.
>>>
>>> Given the document I'm presently working on, I wouldn't really argue with that, except to say that it's still the default assumption in most environments.
>>
>> Yes, and that has deeply impacted both a document I'm working on
>> (draft-ietf-anima-grasp) and a demo implementation thereof
>> (https://github.com/becarpenter/graspy/blob/master/grasp.py).
>>
>> The cost of *not* having link-local multicast is considerable,
>> because it means that every node, however dumb, must replicate
>> and relay discovery in one way or another.
> 
> The solution I briefly described previously of course supports link-local multicast.
> 
> If your answer to the discovery problem is that we must put all nodes on the network in the same broadcast domain, we know that doesn't scale well. 

Of course not. I think both DNSSD and ANIMA have got beyond that point.

...
> Since we have to solve the problem for multiple links anyway, does it then make a difference that logical topology follows physical topology and each host is on its own link?

If the discovery traffic is a very small proportion of total traffic, it probably doesn't matter exactly which solution you adopt. But (as Tim implies for DNSSD), I think you should use link-local multicast when it's available. Are we disagreeing?

    Brian

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