Naive IPv6 (was AT&T UVERSE Native IPv6, a HOWTO)

Brian Dickson brian.peter.dickson at gmail.com
Wed Dec 4 18:21:32 UTC 2013


Rob Seastrom wrote:

> "Ricky Beam" <jfbeam at gmail.com<http://mailman.nanog.org/mailman/listinfo/nanog>>
> writes:
> >
> * On Fri, 29 Nov 2013 08:39:59 -0500, Rob Seastrom <rs at seastrom.com
> <http://mailman.nanog.org/mailman/listinfo/nanog>> wrote: *>>
> * So there really is no excuse on AT&T's part for the /60s on uverse
> 6rd... *>
> * ... *>
> * Handing out /56's like Pez is just wasting address space -- someone *>
> * *is* paying for that space. Yes, it's waste; giving everyone 256 *>
> * networks when they're only ever likely to use one or two (or maybe *>
> * four), is intentionally wasting space you could've assigned to *>
> * someone else. (or **sold** to someone else :-)) IPv6 may be huge to *>
> * the power of huge, but it's still finite. People like you are *>
> * repeating the same mistakes from the early days of IPv4... * There's
> finite, and then there's finite. Please complete the
> following math assignment so as to calibrate your perceptions before
> leveling further allegations of profligate waste.
> Suppose that every mobile phone on the face of the planet was an "end
> site" in the classic sense and got a /48 (because miraculously,
> the mobile providers aren't being stingy).
> Now give such a phone to every human on the face of the earth.
> Unfortunately for our conservation efforts, every person with a
> cell phone is actually the cousin of either Avi Freedman or Vijay
> Gill, and consequently actually has FIVE cell phones on active
> plans at any given time.
> Assume 2:1 overprovisioning of address space because per Cameron
> Byrne's comments on ARIN 2013-2, the cellular equipment providers
> can't seem to figure out how to have N+1 or N+2 redundancy rather
> than 2N redundancy on Home Agent hardware.
> What percentage of the total available IPv6 space have we burned
> through in this scenario? Show your work.
> -r


Here's the problem with the math, presuming everyone gets roughly the same
answer:
The efficiency (number of prefixes vs total space) is only achieved if
there is a "flat" network,
which carries every IPv6 prefix (i.e. that there is no aggregation being
done).

This means 1:1 router slots (for routes) vs prefixes, globally, or even
internally on ISP networks.

If any ISP has > 1M customers, oops. So, we need to aggregate.

Basically, the problem space (waste) boils down to the question, "How many
levels of aggregation are needed"?

If you have variable POP sizes, region sizes, and assign/aggregate towards
customers topologically, the result is:
- the need to maintain power-of-2 address block sizes (for aggregation),
plus
- the need to aggregate at each level (to keep #prefixes sane) plus
- asymmetric sizes which don't often end up being just short of the next
power-of-2
- equals (necessarily) low utilization rates
- i.e. much larger prefixes than would be suggested by "flat" allocation
from a single pool.

Here's a worked example, for a hypothetical big consumer ISP:
- 22 POPs with "core" devices
- each POP has anywhere from 2 to 20 "border" devices (feeding access
devices)
- each "border" has 5 to 100 "access" devices
- each access device has up to 5000 customers

Rounding up each, using max(count-per-level) as the basis, we get:
5000->8192 (2^13)
100->128 (2^7)
20->32 (2^5)
22->32 (2^5)
5+5+7+13=30 bits of aggregation
2^30 of /48 = /18
This leaves room for 2^10 such ISPs (a mere 1024), from the current /8.
A thousand ISPs seems like a lot, but consider this: the ISP we did this
for, might only have 3M customers.
Scale this up (horizontally or vertically or both), and it is dangerously
close to capacity already.

The answer above (worked math) will be unique per ISP. It will also drive
consumption at the apex, i.e. the size of allocations to ISPs.

And root of the problem was brought into existence by the insistence that
every network (LAN) must be a /64.

That's my 2 cents/observation.

Brian


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