Rob Janssen a écrit : > The DNS should be replaced by something that is able to generate dynamic > replies query-by-query. > So, for every query from a user (possibly via a caching server) the DNS > should generate a reply from all information it has available at that time.
Absolutely, you describe pretty much what I would want in a DNS server for this project. I made a prototype using Border Gate Protocol (BGP) data last April -- with mixed results. With hindsight I think that the only factor that must be taken into consideration for NTP is latency. BGP had a tendency of optimizing for bandwidth. I played a bit with Maxmind's GeoIP and Great Circle Distance calculations recently, but I'm not to the point of testing a prototype. It's not very hard or a lot of work, but the weather is so nice outside that I can't stand in front of the computer for very long... :-) > This includes not only the database of pool members, but also the > uptodate reachability information, the recent history of replies sent > to users, the source network of the query, etc. My earlier prototype (and the next ones) used a CDB file (http://cr.yp.to/cdb.html) for storing the information about the NTP servers. That CDB file can be regenerated by a server at pool.ntp.org every few minutes and rsync'd to the DNS servers without any disruption of DNS service. I'm not sure about "the recent history of replies sent to users" though. My prototype would respond to 0.pool.ntp.org with the closest server, 1.pool.ntp.org the 2nd closest, up to 5.pool.ntp.org. What you propose would imply a finite state machine in the DNS server, and I don't think that that would work well with DNS caching servers. As a rule of thumb, I try to keep my designs as stateless as possible. > That would make it possible to distribute the load more evenly and to > give out server addresses that are reasonably close to the requester > without requiring all those different names to be figured out by the > clients. Yes. I'm pretty sure that most users don't use the region/country zones anyway. I guess that it would also make the NTP servers that are close to ISP's customers very popular while the NTP servers in server rooms (far away from the mass) would be less popular. But that's pure speculation, we'll see when we test it. It would be harder to keep accurate data about the number of users of the pool. Now we can take the average number of clients in a server and multiply that by the number of servers in the pool. With a new DNS system, the number of clients would be different for each NTP server. Cheers, GFK's -- Guillaume Filion, ing. jr Logidac Tech., Beaumont, Québec, Canada - http://logidac.com/ PGP Key and more: http://guillaume.filion.org/
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