nested prefixes in Internet

Mon Oct 10 17:24:45 UTC 2016

* r.engehausen at 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.

	-- Niels.