On Thu, Aug 12, 2021 at 1:22 PM 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. 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. > Bill, I beg to respectfully differ, knowing that I'm just a researcher and working `for real' like you guys, so pls take no offence. I don't think A would be right to filter these packets to 10.0.1.0/24; A has announced 10.0.0.0/16 so should route to that (entire) prefix, or A is misleading its peers. If A doesn't, though, then B receives a packet from A to 10.0.1.0/24. Unless B is filtering based on the specific IP prefixes of A - which seems to me unlikely - then B has no way to know that this packet is from `you' rather than from A itself (or a customer of A). So B will carry this traffic, imho. So A is just paying for the traffic since it announced the prefix. Such situations, to best of my knowledge, actually happen on the Internet when a subprefix is filtered for different reasons. We observed it happens with ROV , in our ROV++ simulations, but I'll refrain from attaching the URL again so not to be `plugging' that paper (and since I'm lazy to look it up hhh) have great day and I'll be happy to learn if I'm wrong. Amir
