On Thu, Aug 12, 2021 at 10:19 AM William Herrin <b...@herrin.us> wrote: > On Thu, Aug 12, 2021 at 9:41 AM Hank Nussbacher <h...@interall.co.il> wrote: > > On 12/08/2021 17:59, William Herrin wrote: > > > If you prune the routes from the Routing Information Base instead, for > > > any widely accepted size (i.e. /24 or shorter netmask) you break the > > > Internet. > > > > How does this break the Internet? I would think it would just result in > > sub-optimal routing (provided there is a covering larger prefix) but > > everything should continue to work. Clue me in, please. > > A originates 10.0.0.0/16 to paid transit C > B originates 10.0.1.0/24 also to paid transit C > C offers both routes to D. D discards 10.0.1.0/24 from the RIB based > on same-next-hop > You peer with A and D. You receive only 10.0.0.0/16 since A doesn't > originate 10.0.1.0/24 and D has discarded it. > You send packets for 10.0.1.0/24 to A (the shortest path for > 10.0.0.0/16), stealing A's paid transit to C to get to B. >Unless A filters C-bound packets purportedly from 10.0.1.0/24.
I mashed this sentence together wrong. I meant say: "Unless A filters packets from peers which would use their paid transit," a common policy restriction placed on settlement-free peering. >B > doesn't currently transit for A so from B's perspective that's not an > allowed path. In which case, your path to 10.0.1.0/24 is black holed. > > D broke the Internet. If packets from you reach A at all, they do so > through an unpermitted path. -- William Herrin b...@herrin.us https://bill.herrin.us/