Re: [v6ops] Implementation Status of PREF64

Gert Doering <> Wed, 13 October 2021 17:37 UTC

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Date: Wed, 13 Oct 2021 19:37:46 +0200
From: Gert Doering <>
To: Gert Doering <>, Philip Homburg <>,
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Subject: Re: [v6ops] Implementation Status of PREF64
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On Wed, Oct 13, 2021 at 10:25:36AM -0700, Owen DeLong wrote:
> > So far I have not seen any data that supports "/64 was a good idea" :-)
> It???s working quite well in a number of networks I???ve deployed.
> It???s convenient for EUI-64 addressing.
> Reviewing the record, it seems we were destined for something like 64-bit
> addressing overall before IETF decided to consider EUI-64 addressing and
> added 64-bits to the plan, so one can argue that without the idea of
> universal /64 addressing we???d have a whole lot fewer network numbers
> available.
> So now you have seen data to suggest that /64 was a good idea.
> Do you have any data support your claim that /64 was not?

What part of "yeah, it works for me" makes it a *good* idea?

So did /80s, when they were the latest fashion.

What part of "EUI-64" is a *good* idea, now that everyone is actually
moving away from EUI-64, because it has more undesirable properties than
"oh, yeah, it was there and is convenient"?

Nah.  8+8 was a brilliant idea that did not happen - and nothing else
in a /64 is more than "we can't find consensus to change that".

On the downside:

 - it creates pressure on the number of subnets in reasonably structured
   deployments (think of the number of subnets you can have with a /96
   standard subnet size...)

 - ND exhaustion attacks (which arguably would happen in a /96 just as well)

Gert Doering
        -- NetMaster
have you enabled IPv6 on something today...?

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