Re: Dual stack IPv6 for IPv4 depletion

[Doug Barton <dougb () dougbarton us>]

On 7/15/15 12:43 PM, George Metz wrote:
> On Wed, Jul 15, 2015 at 2:11 PM, Doug Barton <dougb () dougbarton us
> <mailto:dougb () dougbarton us>> wrote:
>
>     On 7/15/15 8:20 AM, George Metz wrote:
>
>
>
> Snip!
>
>     Also, as Owen pointed out, the original concept for IPv6 networking
>     was a 64 bit address space all along. The "extra" (or some would
>     say, "wasted") 64 bits were tacked on later.
>
>         Still oodles of addresses, but worth
>         noting and is probably one reason why some of the "conservationists"
>         react the way they do.
>
>
>     It's easy to look at the mandatory /64 limit and say "See, the
>     address space is cut in half to start with!" but it's not accurate.
>     Depending on who's using it a single /64 could have thousands of
>     devices, up to the limit of the broadcast domain on the network
>     gear. At minimum even for a home user you're going to get "several"
>     devices.
>
> Allow me to rephrase: "A single /32 could have thousands of devices, up
> to the limit of a 10/8 NATted behind it". This, plus the fact that it
> WAS originally 64-bit and was expanded to include RA/SLAAC, is why I
> chose that analogy.

Sure, so in that context it's a valid analogy, but my point still 
stands. We're not talking about routable/PI space for customers, even at 
the /48 level.

Now it is true that the CW seems to be leaning towards /48 being the 
largest routable prefix *for commercial networks*, but that's orthogonal 
to the issue of home users.

>     I do see that as a possibility, however in this world that you're
>     positing, how many of those molecules need to talk to the big-I
>     Internet? Certainly they need to communicate internally, but do they
>     need routable space? Also, stay tuned for some math homework. :)
>
>
> So, you're advising that all these trillions of nanites should, what,
> use NAT? Unroutable IP space of another kind? Why would we do that when
> we've already got virtually unlimited v6 address space?
>
> See what I mean? Personally I'd suspect something involving quantum
> states would be more likely for information passage, but who knows what
> the end result is?

I very carefully tried to skirt the issue, since NAT is a hot-button 
topic for the most ardent of the IPv6 zealots. You were positing a world 
where we need addressing at a molecular level, my point is simply that 
in that world we may or may not be dealing with publicly routable space; 
but *more importantly*, even if we are, we're still covered.

>         I wrote my email as a way of pointing out that maybe the
>         concerns (on
>         both sides)- aren't baseless,
>
>
>     Please note that I try very hard not to dismiss anyone's concerns as
>     baseless, whether I agree with them or not. As I mentioned in my
>     previous message, I believe I have a pretty good understanding of
>     how the "IPv6 conservationists" think. My concern however is that
>     while their concerns have a basis, their premise is wrong.
>
> I wasn't intending yourself as the recipient keep in mind. However, IS
> their premise wrong? Is prudence looking at incomprehensible numbers and
> saying "we're so unlikely to run out that it just doesn't matter"

Yeah, that's totally not what I'm saying, and I don't think even the 
most ardent IPv6 zealot is saying it either. What I'm saying is that 
there is a very solid, mathematical foundation on which to base the 
conclusion that ISPs handing out /48s to end users is a very reasonable 
thing to do.

> or is
> prudence "Well, we have no idea what's coming, so let's be a little less
> wild-haired in the early periods"? The theory being it's a lot harder to
> take away that /48 30 years from now than it is to just assign the rest
> of it to go along with the /56 (or /52 or whatever) if it turns out
> they're needed. I personally like your idea of reserving the /48 and
> issuing the /56.

Thanks. :)  I do recognize that even with all of the math in the world 
we don't know what the world will look like in 20 years, so *some 
degree* of pragmatism is valuable, especially as we're ramping up 
deployment.

But your argument that it'll be hard to take away the /48 is almost 
certainly wrong. This isn't like handling out "Class A's" and "Class 
B's" in the early days of IPv4, when we're talking home users we're 
talking about PA space, which can be withdrawn at will.

Even at the RIR level, assuming some unimaginable future where 400+ /48s 
per human on the planet isn't enough, they can simply revise their 
policies to require justification at some other level per user than /48, 
thereby proclaiming that an ISP's existing space is "adequate" by 
administrative fiat.

In that sense I actually believe that we've learned the lessons from the 
early days of IPv4, and that we've adequately accounted for them in the 
current set of policies.

... and not to flog the expired equine, but we're still only talking 
about 1/8 of the available space. I'm not being snarky when I say that 
we really are dealing with numbers that are so large that it's hard for 
the human mind to comprehend them.

>     That's not splitting the difference. :)  A /56 is half way between a
>     /48 and a /64. That's 256 /64s, for those keeping score at home.
>
>
> It's splitting the difference between a /56 and a /48. I can't imagine
> short of the Nanotech Revolution that anyone really needs eight thousand
> separate networks, and even then... Besides, I recall someone at some
> point being grumpy about oddly numbered masks, and a /51 is probably
> going to trip that. :)

The issue is more nibble boundaries than odd-numbered masks. But my 
point wasn't really to say "/56 is the right answer," since it's not, 
/48 is. :)

> I think folks are missing the point in part of the conservationists, and
> all the math in the world isn't going to change that. While the... let's
> call them IPv6 Libertines... are arguing that there's no mathematically
> foreseeable way we're going to run out of addresses even at /48s for the
> proverbial soda cans, the conservationists are going, "Yes, you do math
> wonderfully. Meantime is it REALLY causing anguish for someone to only
> get 256 (or 1024, or 4096) networks as opposed to 65,536 of them? If
> not, why not go with the smaller one? It bulletproofs us against the
> unforeseen to an extent."

The short answer to your question is, "Yes." The longer answer is that 
we are only just starting down the road of what's going to be possible 
for home users with IPv6. There is already a desire to use multiple 
different subnets, and nested routers. My personal feeling is that 256 
networks (a /56) is going to be enough for the foreseeable future, but 
the point Owen has made quite eloquently is that we don't want to 
hamstring these efforts from the outset with something ludicrously small.

So it really isn't a matter of not understanding the conservationists, 
it's more a matter that the math really does work. But even given all 
that, I still advise to reserve the /48, and allocate the /56, then as 
the next couple of years go by it will become increasingly obvious what 
the right answer is, and no matter who was "right" we'll still have all 
the space we need. I'm glad that we seem to have reached agreement on 
that point at least. :)

Doug

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