Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]

Fernando Gont <fgont@si6networks.com> Mon, 16 January 2017 21:15 UTC

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Subject: Re: IID length text [was Re: Review of draft-ietf-6man-rfc4291bis-06]
To: Brian E Carpenter <brian.e.carpenter@gmail.com>, Lorenzo Colitti <lorenzo@google.com>
References: <148406593094.22166.2894840062954191477.idtracker@ietfa.amsl.com> <m2fukqbbwv.wl-randy@psg.com> <F6953234-3F85-4E28-9861-433ADD01A490@gmail.com> <m2wpdzhncn.wl-randy@psg.com> <82245ef2-cd34-9bd6-c04e-f262e285f983@gmail.com> <m2d1frhjfn.wl-randy@psg.com> <18e6e13c-e605-48ff-4906-2d5531624d64@gmail.com> <CAKD1Yr1cvZ8Y3+bHeML=Xwqr+YgDspZGnZi=jqQj4qe2kMc4zw@mail.gmail.com> <m2lguffnco.wl-randy@psg.com> <CAKD1Yr1TrTiPRdyutobmb_77XJ7guNzLrg=H_p7qi4BfQ8V=GA@mail.gmail.com> <m2d1frfm6m.wl-randy@psg.com> <CAKD1Yr2Njjd8_Mr+6TRFF6C5pdcX4yFgpFVyEkykDuytu2B8mg@mail.gmail.com> <2A5073777007277764473D78@PSB> <4596c3d4-a337-f08e-7909-f14270b7085f@gmail.com> <CAN-Dau06R3iYRpYLADhvHox4C9qdsJCuxFsJapRhOQcWT4qk_g@mail.gmail.com> <CAO42Z2weZcoHiBzN94QAQ9WGhWR16PmMMFNg=5YLmr_dhPjjpA@mail.gmail.com> <fcf580ec-3617-ca5f-5337-37acb6e928ba@gmail.com> <CAKD1Yr25zNeQGvNJa=WzCjKMd9LaYrSwG=o4tUWn1Zc2ASZjrA@mail.gmail.com> <93700502-5d49-86ce-11b0-ab9904423961@gmail.com>
From: Fernando Gont <fgont@si6networks.com>
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On 01/16/2017 04:57 PM, Brian E Carpenter wrote:
> On 16/01/2017 22:36, Lorenzo Colitti wrote:
>> Brian,
>>
>> what's the specific rationale for this change? Is it a bug in 4291 which
>> you're proposing that we resolve in 4291 bis? If so, what is the bug?
> 
> The bug is that in SLAAC, the IID length is a parameter, not a constant,
> and that in routing protocols, the prefix length is a parameter, not
> a constant. The addressing architecture needs to recognise that.

+1



>> The "interface identifiers are 64 bits" long text in RFC 4291 goes back all
>> the way to 1998 and the text below would be a major change to text that has
>> likely been baked into implementations for almost two decades years. I
>> don't see why we would change that now.
> 
> Any SLAAC implementation that has 64 baked into it is already non-conformant.
> But I very much doubt if anyone will need to change their code as a result
> (except for any non-conformant routers such as you mentioned recently).

+1


>> In general, IPv6 addresses are
>> aggregatable on all bit lengths. But global unicast addresses (other than
>> ::/3) have a 64-bit IID, so links in that space are assigned 64-bit prefix
>> lengths. These two properties can coexist even in global unicast space. For
>> example, you could load-balance traffic to a given global unicast /64 by
>> announcing it to the backbone as two /65s. The "addresses are aggregatable
>> on all bit lengths" text means that the /65 are valid prefixes that can be
>> routed by routers.
> 
> Sure. And this text doesn't aim to change anything in any current (and
> non-broken) implememtations. It aims to respond to the objections that have
> been discussed on the IETF list recently.

Agreed.

(Thanks for proposing text, btw!)

-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
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