Lanlan Pan wrote: > ... Because ECS is also based on the map of > "*client subnet -> geolocation*" information.
Paul Vixie <p...@redbarn.org>于2017年3月22日周 > wait, what? Lanlan Pan wrote: > Hi Paul, hi. > https://www.cdnplanet.com/blog/which-cdns-support-edns-client-subnet/ this web page is factually incorrect in that it presupposes that geo-ip is used. i have added a comment there to this effect. the original ECS web site (http://www.afasterinternet.com/howitworks.htm) is somewhat marketing-oriented, but says only that "With this more intelligent routing, customers will have a better Internet experience with lower latency and faster speeds." in other words, it expects that a CDN will apply its server-selection logic on an address basis, but using the truncated client subnet rather than to the DNS request source address. it does not dictate what the CDN's server-selection logic has to be or do. in RFC 7871 (http://www.afasterinternet.com/ietfrfc.htm) we see this definition: > Topologically Close: Refers to two hosts being close in terms of the > number of hops or the time it takes for a packet to travel from > one host to the other. The concept of topological distance is > only loosely related to the concept of geographical distance: two > geographically close hosts can still be very distant from a > topological perspective, and two geographically distant hosts can > be quite close on the network. there is an error on page 22 which is directly on-point: > o Recursive Resolvers implementing ECS should only enable it in > deployments where it is expected to bring clear advantages to the > end users, such as when expecting clients from a variety of > networks or from a wide geographical area. Due to the high cache > pressure introduced by ECS, the feature SHOULD be disabled in all > default configurations. from context, it's clear that they meant "topological area". actual CDN technology, from as far back as Cisco Distributed Director in the mid-1990's, has usually ignored geography, for the reasons i gave up-thread: overlapping and incoherent topology within a geo-ip region means that geo-location is a very poor predictor of per-path performance. let me state (again) for the record that i was and remain opposed to ECS because it's an obviously bad idea and the apparent need for it merely proves that Stupid DNS Tricks (http://queue.acm.org/detail.cfm?id=1647302) did not and could not solve their chosen problem in the first place. it's architectural cost-shifting, which is a form of both intellectual conversion and economic compulsion. sad! however, if you're going to propose a replacement for ECS, you should correctly describe how it works. <<Because ECS is also based on the map of "*client subnet -> geolocation*">> is not a correct description. if EIL is geo-based, then it is completely different from ECS. -- P Vixie _______________________________________________ DNSOP mailing list DNSOP@ietf.org https://www.ietf.org/mailman/listinfo/dnsop
