Hi, all-- On Oct 22, 2010, at 9:37 AM, pateretou Pateretou wrote: > Hello, > I'm so embarrassing with this stupid question but I'm not very comfortable > with the "peer select algorithm" > > Let me try to explain: > I've got one GPS stratum 1 server located in New York (172.17.200.100) and > one GPS stratum 1 server located in London (172.17.100.100). > in each datacenter approx 200 servers sync on BOTH servers > > ntp.conf: > server 172.17.100.100 minpoll 4 maxpoll 4 > server 172.17.200.100 minpoll 4 maxpoll 4 > > I would like servers in london sync to the London GPS and servers in NY sync > with the NY GPS (seems to be a coherent choice, isn't it?)
Sure, and you can add the "prefer" keyword to cause NTPd to try and use a particular NTP server for syncing, unless something appears obviously wrong with it. Anyway, given the # of clients, I would be strongly tempted to set up three machines in each data center, all referencing each others as peers and referencing either the non-local NTP server in the other data center, or some other public stratum-1 or -2 NTP source for highest redundancy, because NTP clock selection algorithm can do a better job if at least 4 timeservers are configured. For your client boxes, either setup a DNS alias like time-ny.example.com & time-london.example.com which lists A records for the three IPs of the local timeservers in the corresponding data center, and just have a single "server time-ny.example.com" line for the client configs, or do something like: London client machines ntp.conf: server 172.17.100.100 iburst prefer server 172.17.100.101 iburst server 172.17.100.102 iburst server 172.17.200.100 NY client machines ntp.conf: server 172.17.200.100 iburst prefer server 172.17.200.101 iburst server 172.17.200.102 iburst server 172.17.100.100 ...assuming you'd setup .101 & .102 as additional NTP servers. The default poll intervals for the client machines should be fine; keep using maxpoll 4 for traffic between the designated NTP servers, if you like. > The problem is all my servers are the NY server in "sys.peer". But the only > "difference" between my timeserver with my servers in london is the delay is > bigger with the NY server so I don't understand why my server use the NY > server for sync and not the london server > > $ ntpq -pn > remote refid st t when poll reach delay offset jitter > ============================================================================== > +172.17.100.100 .PPS. 1 u 9 16 377 0.178 0.007 > 0.008 > *172.17.200.100 .PPS. 1 u 8 16 377 67.203 0.009 > 0.010 > > Why my servers are sync with the most away time server? Checking the details of the status messages suggests that the London timeserver claims a precision of -19, but NY claims -20. If everything else is identical, ntpd likes the higher precision source-- higher network delay doesn't really matter if it is consistent, and your jitter results suggest that the delay is quite consistent.... Regards, -- -Chuck _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
