IPv6 Addressing Help

William Herrin herrin-nanog at dirtside.com
Fri Aug 14 23:38:12 CDT 2009

On Fri, Aug 14, 2009 at 8:15 PM, Nathan Ward<nanog at daork.net> wrote:
> you are reinventing
> classful addressing, and when one POP or city grows too large, you have to
> make exceptions to your rules.


I'm going to contradict you there. Classful addressing had a lot to
recommend it. The basic problem we ran in to was that there weren't
enough B's for everyone who needed more than a C and there weren't
enough A's period. So we started handing out groups of disaggregate
C's and that path led to the swamp.

CIDR too is the architect of its own demise. With address assignments
all mixed together, we lack clean boundaries by which we can identify
the multihomed orgs amidst the disaggregation for traffic engineering.
Thus Bell South announces 4200 routes and we carry them all with an
annual systemic cost in the neighborhood of $30M. The route table
continues to grow beyond our control.

With IPv6 we have more than enough addresses to give a /56 to
everybody who needs more than a /60 and a /48 to everybody who needs
more than a /56. A rapidly escalating assignment series like this
would place a strong upper bound on the number of routes needed for
any one entity regardless of how they grow. Allocating from pools
reserved solely for specific prefix sizes should enable the
compression of distant TE disaggregation.

Maybe it's worth considering the benefits of a classful-like
addressing before casually discarding it as yesterday's news.

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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