Re: draft-bourbaki-6man-classless-ipv6-00

[David Farmer <[e-mail]>]

On Fri, Jun 9, 2017 at 1:36 AM, Lorenzo Colitti <[e-mail]> wrote:

> On Fri, Jun 9, 2017 at 1:24 PM, Fernando Gont <[e-mail]>
> wrote:
>
>> > However, I think IPv6 implementations that don't support manual
>> > configuration must be able to reject non-64 bit IIDs, since that is the
>> > standard. Saying "SHOULD be 64 bits long" means they "MAY be /81, /99 or
>> > /123", and those are against BCP 204 (RFC 7934).
>>
>> BCP204 talks about multiple addresses. As long as whatever prefix is
>> employed allows for multiple addresses, I don't see how that goes
>> against BCP204.
>
>
> That's not true at all. As an example: see if you can build a network that
> uses a /99 and satisfies the recommendations in section 8 or BCP 204.
>

Yes, to meet the specific RECOMMENDATIONS in BCP204 /64 is necessary.
However, the fundamental intent of BCP 204 is that general-purpose hosts
should get as many addresses as they reasonably want, in some
situation hundreds
or thousands of addresses could be consider unreasonable.  I'll note it
doesn't directly speak to security or privacy consideration such as
randomized assignment or even suggest sparse assignment, it does reference
RFC7217 in the Common IPv6 Deployment Model section, but that's it. So, in
short BCP204 is fundamentally about making sure hosts have many addresses
available to them.

It seems to me that extremely long prefixes like /120 or longer are likely
unable to achieve the intent of BCP204 for any significant number of hosts.
However, anything in the range /112 or shorter should have plenty of
address to achieve the intent of BCP204 for a quite reasonable numbers of
hosts, at least many hundreds of hosts.

So, of the examples you provided, /123 is unlikely to achieve the intent of
BCP204, but /81 or /99, while they don't meet the specific RECOMMENDATIONS
of BCP204 there doesn't seem to be any reason they couldn't achieve the
fundamental intent of BCP204, granted with without much sparseness or
entropy in the assignments, but that's not specifically part of BCP204.

Thanks.



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