>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. 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. > >Regards, >Bill Herrin
Ok, I apologize, but I have some dumb questions (because I don't BGP anymore): 1) I assume in the scenario that A "owns" (ARIN assignment) 10.0.0.0/16 and if B has a /24 assignment out of the block that A "owns", shouldn't that mean that B has a business relationship with A and some kind of direct connectivity to A? 2) If "no", then why is B using a /24 out of A's block? If A sold or gave the block to B without a connectivity agreement, then A should break up their announcements appropriately to carve the /24 out of their announcement, right? 3) If "yes", then the connectivity wouldn't be broken, right? TIA for the tutoring and bearing with me. Regards, Jason K Pope
