Subject: RE: IPv6 Addr/Prefix clarification

From: "Michel Py" <[email-masked]>
Date: Wed, 23 Jan 2002 08:09:57 -0800

> Irina Dayal wrote:
> 1) Is it safe to assume that all IPv6 prefixes will be between 16 and 64
> bits long?  The current allocation of IPv6 prefixes seems to require
> Aggregatable Global Unicast Addresses, which restricts the prefixes to
> this range.

It's not safe (even if it might be true today). Slightly more than 1/8 of
the IPv6 address space has been allocated to a purpose so far. There are
drafts that are mentionning allocating 0001, which is a /4.

Even today, one might want to configure 2000::/3 as the default route
instead of 0::/0.

Michel.

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From: "Michel Py" <[email-masked]>
Date: Wed, 23 Jan 2002 10:12:30 -0800

> Tony Hain wrote:
> 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 ...

Correct. Technically, a lot is possible. However, I think we have
to discourage people to subnet the IID. Doing so will also void
things like EUI-64 and future 64-bit MAC addresses. Also, there are
issues with link-local addresses. How good is it to have a
link-local address if you can subnet it. That is why site local
addresses are for, they use the 16 SLA bits. My reading of link-local
addresses is that they can not be subnetted further than a /64.

Michel.

---

From: "Michel Py" <[email-masked]>
Date: Thu, 31 Jan 2002 19:12:52 -0800

I fully concur with Tony and this should be the end of the thread.

Michel.

	-----Original Message-----
	From:	Tony Hain [SMTP:[email-masked]]
	Sent:	Thursday, January 31, 2002 5:06 PM
	To:	Michel Py; Keith Moore
	Cc:	[email-masked]
	Subject:	RE: IPv6 Addr/Prefix clarification 

	You are both right and wrong... ;)

	We can never prevent a site from internally subnetting on any boundary
	it chooses, but we should be very clear about the consequences. At the
	same time we have to be consistent in our discussions with the rir's and
	providers about making sure sites have at least the options of /48 &
	/64, and that attempts to allocate less will result in ugly hacks that
	will be hard for them to maintain.

	The strongest reason to make this a hard architectural boundary is to
	simplify the dev/test/interoperability of the code for the platform
	vendors. Sites that accept a /64 are stuck with a single subnet, unless
	they have sufficient technical knowledge to break the architecture; and
	have the appropriate support from their platform vendors. We are not in
	a position to prevent architectural abuse (even in our documentation;
	see RFC3022), but we can set expectations and interoperability
	requirements.

	If a site receives a /64 from their provider, the simplest approach
	would be to bridge the environment. For those that want a more complex
	topology, they will be better-off to lobby their provider for more
	space. Given track records, this is likely to be possible for a simple
	matter of more money. For those who don't want to pay for address space,
	but do want to pay for the cost of local implementations which subnet
	longer than /64, they are free to do so. One might point out this is a
	false economy, but people don't always listen.

	Tony

	> -----Original Message-----
	> From: [email-masked]
	> [mailto:[email-masked]]On Behalf Of Michel Py
	> Sent: Thursday, January 31, 2002 4:29 PM
	> To: Keith Moore
	> Cc: [email-masked]
	> Subject: RE: IPv6 Addr/Prefix clarification
	>
	>
	> >>> Keith Moore wrote:
	> >>> By allowing sites to subnet /64s we aren't forcing them to give up
	> >>> autoconfig, private addresses, etc...
	>
	> >> Michel Py wrote:
	> >> Would you educate me on how you do autoconfig, let's say,
	> on a /85 ?
	>
	> > Keith Moore wrote:
	> > you don't.  a site that chooses to subnet below /64 is inherently
	> > choosing not to use stateless autoconfig.  but this is a choice for
	> > that site to make, not for us to make on that site's behalf.
	>
	> This is direct contradiction with what you wrote before.
	>
	> > you still haven't given a single argument in favor of not allowing
	> > sites to subnet below /64.
	>
	> Yes, I have. And you haven't yet given a single good reason why a site
	> should subnet below /64, when a site should, indeed, use the SLA bits
	> (means SITE LEVEL AGGREGATOR) which have been designed for that very
	> purpose.
	>
	> Michel.
	>