[arin-ppml] Rationale for /22

[Kevin Kargel]

> 
> On Mon, Aug 3, 2009 at 11:30 AM, Stephen Sprunk<stephen at sprunk.org> wrote:
> >> I can't see any detraction from getting providers to get an
> >> ARIN-assigned /24 instead of having to get a /24 from one provider
> >> and route it out another, being historically on the "purchasing"
> >> side of that arrangement.
> >
> > There is one major difference: if you get a /24 from your upstream and
> > other folks in the DFZ filter it, you can still be reached via your
> > upstream's aggregate.  If you have a PI /24, there is a much greater
> > chance of breakage.
> 
> Hi Stephen,
> 
> We've discussed this point several times in this thread. The bottom
> line: nobody actually does this any more, at least not that we've been
> able to identify.
> 
> In the 2009 backbone, you either carry "full" routes down to /24 or
> you carry partial routes and a default. The default takes you to
> someone who does carry full routes. Whether those partials are
> composed by filtering on the RIR minimums or using some other criteria
> (e.g. distant routes) makes little difference.
> 
> IMHO, that's the reality on the ground that ARIN policy should target,
> not a hypothetical network in which folks carry partial routes without
> a default and it works out for them.
> 
> Regards,
> Bill Herrin
> 
As a piece of trivia, I know of one small multihomed ISP who runs BGP to
announce routes, carries no routes at all except for direct connected peers
and has two default routes with some rather complex priorities and mapping
to upstreams that do carry full routes and it seems to work quite well for
them.  

Kevin
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