A crazy idea

Randy Bush randy at psg.com
Mon Jul 19 16:37:14 UTC 2021

On Mon, 19 Jul 2021 09:27:13 -0700,
Nathan Angelacos wrote:
> On Mon, 2021-07-19 at 08:51 -0700, Randy Bush wrote:
> > > Well, for SLAAC you need a /64
> > 
> > this is not true
> > 
> > randy
> That is cool!   Can you point me to the correct RFC please?

from the war zone, draft-classless6/draft-nbourbaki-6man-classless-ipv6

   The length of the Interface Identifier in Stateless Address
   Autoconfiguration [RFC4862] is a parameter; its length SHOULD be
   sufficient for effective randomization for privacy reasons.  For
   example, 48 bits might be sufficient.  But operationally we
   recommend, barring strong considerations to the contrary, using
   64-bits for SLAAC in order not to discover bugs where 64 was hard-
   coded, and to favor portability of devices and operating systems.

   Note that OpenBSD ships with SLAAC for lengths longer than /64.

   Nonetheless, there is no reason in theory why an IPv6 node should not
   operate with different interface identifier lengths on different
   physical interfaces.  Thus, a correct implementation of SLAAC must in
   fact allow for any prefix length, with the value being a parameter
   per interface.  For instance, the Interface Identifier length in the
   recommended (see [RFC8064]) algorithm for selecting stable interface
   identifiers [RFC7217] is a parameter, rather than a hard-coded value.

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