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Re: IPv6 end user addressing
From: Jeff Wheeler <jsw () inconcepts biz>
Date: Sat, 6 Aug 2011 06:15:01 -0400

On Sat, Aug 6, 2011 at 5:21 AM, Owen DeLong <owen () delong com> wrote:
At least don't make your life miserable by experimenting with too many different assignment sizes,
or advocate /64s or something, that's considered a design fault which will come back to you some day.
Read the RfCs and RIR policy discussions in the archives some years ago.

Note that in this thread, you advocate three things that are a little
tough to make work together:
* hierarchical addressing plan / routing
* nibble-aligned addressing plan
* minimum /48 per customer

If I were, for example, a hosting company with IPv6 terminated at the
layer-3 ToR switch, I would then use a /40 per rack of typical
"dedicated servers."  If you then want some bits to be a POP-locator
field for your hierarchical routing scheme, you are already forced to
request more than a /32.  The number of customers per layer-3 device
for typical end-user access networks was around the same into the
late-1990s/early-2000s, as ISPs had racks of Portmasters or whatever
box of choice for terminating dial-up.

Densities have changed, but this doesn't necessarily win you an
advantage when combining those three properties.  This is especially
true if you consider that density may change in a difficult-to-predict
manner in the future -- a BRAS box with a couple thousand customers
today might have three times as many in a couple of years (IPv6 is
supposed to help us avoid renumbering or injecting additional routes
into our network, right?)  As an access provider, if I shared your
view, I would be reserving a /36 or /32 per BRAS box.  If I then want
some additional bits for hierarchical routing ... I'm going to need a
pretty large address block for perhaps a pretty small number of
customers.  After all, my scheme, applying your logic, dictates that I
should use a /32 or perhaps a /28 per each POP or city (I need to plan
for several BRAS each), even if I don't have a lot of customers today!

I think /56 is more sensible than /48, given the above, for most
end-users.  Either way, the users will be gaining a lot more
flexibility than they have with IPv4 today, where they probably get
just one IP address and have to pay a fee for any extras.  Giving the
typical end-user 8 fewer bits worth of address space allows the ISP
network more flexibility for hierarchical routing before they have to
go to their RIR and figure out how to justify an out-sized allocation.

Also, if folks would stop thinking that every subnet should be a /64,
they will see that end-users, makers of set-top-gateways, or whatever,
can certainly address a whole lot of devices in a whole lot of subnets
even if the user is only given a /64.  Do we think DHCPv6 won't be the
most common way of assigning addresses on SOHO LANs, and that SLAAC
will be essential?  I, for one, think that some ISPs will be sick and
twisted enough to hand out /128s so they can continue charging for
more IP addresses; but certainly the makers of IPv6-enabled devices
will foresee that end-user LANs might not be /64 and include the
necessary functionality to work correctly with smaller subnets.

Before you beat me to it, yes, we seem to have completely opposing
views on this subject.  I will change my mind when I can go to the RIR
and get a IPv6 /24 for a small ISP with a few POPs and a few tens of
thousands of customers.  Should RIR policy permit that sort of thing?

-- 
Jeff S Wheeler <jsw () inconcepts biz>
Sr Network Operator  /  Innovative Network Concepts


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