IPv6 Ignorance

William Herrin bill at herrin.us
Tue Sep 18 06:35:43 UTC 2012

On Mon, Sep 17, 2012 at 2:16 PM, Owen DeLong <owen at delong.com> wrote:
> We thought 32 bits was humongous in the context of a research project
> that would connect universities, research institutions and some military
> installations.
> In that context, 32 bits would still be humongous.
> Our estimation of humongous didn't change, the usage of the network
> changed dramatically. The experiment escaped from the laboratory
> and took on a life of its own. Once that happened, the realization that
> 32 bits wasn't enough was very nearly immediate.
> The IPv6 address space offers 61 bits of network numbers each of which
> holds up to 64 bits worth of hosts. Obviously you never want to fill one
> of those subnets (nor could you with any available hardware), but it means
> that you don't have to waste time thinking about rightsizing network
> assignments.

Hi Owen,

We think 64 bits is humongous on an IPv4 Internet where
autoconfiguration is rarely bordering never larger than a single LAN.

But, we want the fridge to get a /64 from the home automation
controller for its internal sensor network. Which means the home
automation controller will be holding something around a /58 or so in
order to accommodate the various smart devices in the house. Which
means the the cable router will be holding a /54 or more to
accommodate the server lan, the home automation delegation, the PC
lan, the VM delegation, the wifi lan, etc. And at a customer boundary
we'll only break at a nibble boundary, so that brings us to /52. Which
is inconvenient since we often have larger users so we'll just break
at /48 for everybody.

Then we need 32 bits to overlay the customer's IPv4 address for
convenience within our 6RD network. So that leaves us 16 bits. But we
don't want the native network to overlay the 6RD network because we
want a real simple /16 route into the nearest 6rd encapsulator. And we
don't want to advertise multiple BGP prefixes either. So we claim
another bit and allocate our native infrastructure from the /16 that
doesn't overlap the 6rd setup.

3 bits are held in reserve at the top; only 2000::/3 is available for
public Internet use. So that drops us from 15 to 12 bits. Now we want
to organize the BGP backbone and we've 12 bits left to work with.
That's 4 bits less than the number of autonomous systems participating
in BGP on Internet today.

Of course this is in many ways a straw man. And I'm picking on you
Owen because in the past you've advocated both /48's for end users and
6rd justifying 32 bits of allocation above that from the registry. But
really, with the right (or maybe I mean wrong) hierarchic network
auto-configuration technologies it's not hard to imagine how the IPv6
address space could be exhausted in 20 years.

Bill Herrin

William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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