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RE: Updated IID length text

"Manfredi, Albert E" <albert.e.manfredi@boeing.com> Thu, 19 January 2017 03:24 UTC

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From: "Manfredi, Albert E" <albert.e.manfredi@boeing.com>
To: Lorenzo Colitti <lorenzo@google.com>
Subject: RE: Updated IID length text
Thread-Topic: Updated IID length text
Thread-Index: AQHScexT724zBn76p0KKsEzsg727/qE/EBsQgACTkID//320gA==
Date: Thu, 19 Jan 2017 03:24:14 +0000
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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> <fcc7f136-b5da-527e-b495-5a2d7f7a3ce8@gmail.com> <55bb8bdbfbf4439da0aa702e5bc03e2c@XCH15-06-11.nw.nos.boeing.com> <CAKD1Yr2vmDkUTvSw7-GtKNeMDm1xtAppj+EW9X=-TeKZ6qkXrg@mail.gmail.com>
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From: Lorenzo Colitti [mailto:lorenzo@google.com] 

>> Now that we have moved away from using the MAC address for SLAAC, it's
>> not clear to me why a host cannot wait for a RA, and then decide on
>> how many IID bits to use, based on the prefix length(s) advertised by
>> the router.
>
> The reason it can't do that is that in practice SLAAC only works well
> if the probability of collision is negligible. Even reducing that from
> 64 bits to 48 bits impacts that substantially.

Perhaps, but SLAAC has been deemed to work adequately well with only the 48-bit MAC address (presumably) being unique. So nothing would change in this "negligible collision" regard, if we allowed for 80-bit prefixes with SLAAC. You'd want to do duplicate address detection regardless.

Back in the 1980s, it probably seemed that 32 bits, to identify research computers, was way more than adequate. Clearly, people had not anticipated how this Internet was going to be used. Same applies now.

Bert

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