[arin-ppml] Rationale for /22

William Herrin bill at herrin.us
Wed Jul 29 03:14:25 EDT 2009

On Wed, Jul 29, 2009 at 12:48 AM, Jon Lewis<jlewis at lewis.org> wrote:
> On Tue, 28 Jul 2009, William Herrin wrote:
> Ok, there are a few assumptions in the scenario I suggested.
> 1) "Tier 1's" "don't filter"...i.e. not for route table reduction.
> 2) Any network that does filter for the purpose of route reduction carries a
> default route pointing towards a network that doesn't doesn't filter or that
> points default at one that doesn't.  This could go on for several AS's.
>> As a transit AS you really can't get away with that. If you don't
>> carry all the routes down to /24, your customers will see routing
>> anomalies.
> I got away with it.  I suspect lots of other transit AS's have.

Hi Jon,

Okay. You've described a circumstance based on today's approach of
assigning multihomed blocks smaller than /22 from ISP's space where
99% of the backbone routers carry the small multihomer's /24 and the
other 1% do something that is probably but not definitely reasonable
enough to maintain full connectivity. So drawing this back to the
topic of the discussion: address assignment for small multihomed

Are you just offering an interesting corner case in today's routing
system? Or do you propose that this... morass... is actually a
*healthy* result of the status quo?

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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