Re: nested prefixes in Internet

[Baldur Norddahl <baldur.norddahl () gmail com>]

Den 10/10/2016 kl. 19.24 skrev Niels Bakker:
> * r.engehausen () gmail com (Roy) [Mon 10 Oct 2016, 19:19 CEST]:
> > I don't think I ever said that ISP-B would announce the /19.  That 
> > would only be announced by ISP-A.  ISP-B would only announce the /24 
> > that has been delegated to it.
> >
> > If the ISP-A/ISP-B link goes down then the /24 would be seen only via 
> > ISP-C which is the desired result.
>
> What if ISP-A then receives traffic inside its /19 destined for 
> ISP-B's /24?  It will have to send it over transit and won't bill 
> ISP-B for that traffic.  You cannot expect 100% of the rest of the 
> Internet to honour the more specific all the time.

Is that a real problem? In my experience a /24 is honoured almost 
universially.

If we assume the big tier 1 transit providers honour the /24 
announcement, the only possible way for ISP-A to receive traffic via the 
/19 is if ISP-A is directly peered with someone that ignores the /24.

Even if some small amount of traffic does go that route, it might not be 
viewed as a problem as the volume is likely to be very low.

Regards,

Baldur