On Aug 16, 2015, at 8:15 AM, Job Snijders <j...@instituut.net> wrote: > On Sun, Aug 16, 2015 at 08:00:55AM -0400, Patrick W. Gilmore wrote: >> On Aug 15, 2015, at 1:41 PM, Job Snijders <j...@instituut.net> wrote: >>> On Sat, Aug 15, 2015 at 11:01:56PM +0530, Glen Kent wrote: >> >>>> Is there a paper or a presentation that discusses the drops in the core? >>>> >>>> If i were to break the total path into three legs -- the first, middle >>>> and the last, then are you saying that the probability of packet loss >>>> is perhaps 1/3 in each leg (because the packet passes through >>>> different IXes). >>> >>> It is unlikely packets pass through an IXP more then once. >> >> “Unlikely”? That’s putting it mildly. >> >> Unless someone is selling transit over an IX, I do not see how it can >> happen. And I would characterize transit over IXes far more >> pessimistically than “unlikely”. > > There is another scenario (which unfortunatly is not that uncommon) > where packets could traverse two IXPs, and no transit is sold over any > of those two IXs. > > Imagine the following: > > Network A purchases transit from network B & network C. Network B & > Network C peer with each other via an IXP. Network A announces a /16 to > network B but 2 x /17 to network C. Network D peers with B via an IX > (and not with C) and receives the /16 from B, but note that internally > network B has two more specifics covering the /16 received from C and > the /16 itself. Network B will export the /16 (received from customer) > but not the /17s (received over peering) to its peers. > > Because of longest prefix matching, network B will route the packets > received from network D over an IXP, towards network C, again over an > IXP. > > This phenomenon is described extensively in the following > Internet-Draft: > > https://tools.ietf.org/html/draft-ietf-grow-filtering-threats-07
Good point. Although I have trouble believing it is very common, in the sense that I do not believe it is a large number of packets or percent of traffic. To be clear, I fully believe people are doing the more specifics to provider B but not C. Sometimes there is even a good reason for it (although probably not usually). However, most of the Internet will send traffic directly to B, or even A - especially since most packets are sourced from CDNs[*]. -- TTFN, patrick [*] I’m counting in-house CDNs like Google, Netflix, and Apple as “CDNs” here. Before anyone bitches, trust me, I am probably more aware of the difference between those and a “real” CDN than nearly anyone else. But those distinctions are orthogonal to the discussion at hand.