i loved the henry ford analogy -- but i think henry ford would have said that the automatic transmission was a huge step forward since he wanted everybody to have a car. i can't think of anything that's happened in the automobile market that henry ford wouldn't've wished he'd thought of. i knew that the "incoherent DNS" market would rise up on its hind legs and say all kinds of things in its defense against the ACM Queue article, and i'm not going to engage with every such speaker. there three more-specific replies below. Dave Temkin <davet1@gmail.com> writes:
Alex Balashov wrote:
For example, perhaps in the case of CDNs geographic optimisation should be in the province of routing (e.g. anycast) and not DNS?
In most cases it already is. He completely fails to address the concept of Anycast DNS and assumes people are using statically mapped resolvers.
"anycast DNS" appears to mean different things to different people. i didn't mention it because to me anycast dns is a bgp level construct whereby the same (coherent) answer is available from many servers having the same IP address but not actually being the same server. see for example how several root name servers are distributed. <http://www.root-servers.org/>. if you are using "anycast DNS" to mean carefully crafted (noncoherent) responses from a similarly distributed/advertised set of servers, then i did address your topic in the ACM Queue article. David Andersen <dga@cs.cmu.edu> writes:
This myth ... was debunked years ago:
"DNS Performance and the Effectiveness of Caching" Jaeyeon Jung, Emil Sit, Hari Balakrishnan, and Robert Morris http://pdos.csail.mit.edu/papers/dns:ton.pdf
my reason for completely dismissing that paper at the time it came out was that it tried to predict the system level impact of DNS caching while only looking at the resolver side and only from one client population having a small and uniform user base. show me a "trace driven simulation" of the whole system, that takes into account significant authority servers (which would include root, tld, and amazon and google) as well as significant caching servers (which would not include MIT's or any university's but which would definitely include comcast's and cox's and att's), and i'll read it with high hopes. note that ISC SIE (see http://sie.isc.org/ may yet grow into a possible data source for this kind of study, which is one of the reasons we created it.) Simon Lyall <simon@darkmere.gen.nz> writes:
I heard some anti-spam people use DNS to distribute big databases of information. I bet Vixie would have nasty things to say to the guy who first thought that up.
someone made this same comment in the slashdot thread. my response there and here is: the MAPS RBL has always delivered coherent responses where the answer is an expressed fact, not kerned in any way based on the identity of the querier. perhaps my language in the ACM Queue article was imprecise ("delivering facts rather than policy") and i should have stuck with the longer formulation ("incoherent responses crafted based on the identity of the querier rather than on the authoritative data"). -- Paul Vixie KI6YSY