Subject: RE: IPv6 Addr/Prefix clarification

From: Steve Deering <[email-masked]>
Date: Thu, 7 Feb 2002 16:57:55 -0800

At 11:18 AM -0800 1/23/02, JJ Behrens wrote:
>Please forgive me for being a newbie, but it seems wise to allow
>subnetting of the lower 64 bits. Afterall, it would be terrible if my
>dialup ISP assigned a /64 to me, and I had to rely on some IPv6 mythical
>NAT to do subnetting!

The IAB/IESG recommendation to the registries, which has subsequently
been adopted by all of them, is that the default/standard unit of
allocation to all end subscribers is a /48, and when they judge an
ISP's utilization rate of IPv6 space, it will be on the basis of /48s
per subscriber.  Of course, the registries have no enforcement power
that can prevent an ISP from making smaller allocations (i.e., longer
prefixes), so we hope that market forces will do the job.  At least
an ISP will not be able to justify a longer prefix by claiming shortage
of address space or registry requirements.

Steve

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From: JJ Behrens <[email-masked]>
Date: Wed, 23 Jan 2002 11:18:18 -0800 (PST)

> From: Tony Hain <[email-masked]>
> Keith is technically correct, a site may choose to subnet the low 64
> bits. It might be unwise to do so, because they would be giving up the
> autoconfiguration & privacy capabilities, but that is their choice. They
> may also find acquiring routing hardware that works beyond the 64 bit
> prefix to be a challenge ...

A /64 is really quite a lot of address space to subnet; without the
ability to subnet, a /64 seems wasteful. In response to the address
autoconfiguration using MAC addresses argument, address autoconfiguration
can be done using something other than the MAC address in those
circumstances. The fact that neighbor solicitations are used to verify the
uniqueness of tentative addresses is proof enough that MAC addresses were
never meant to be the end all and be all of address autoconfiguration.

 -jj