David Woolley wrote: > Danny Mayer wrote: >> David Woolley wrote: >>> Richard B. Gilbert wrote: >>> >>>> Sort of! Two servers is generally a poor choice. If they differ, as >>>> they inevitably will, which one should you believe? 'Prefer' will tell >>> If they differ enough for voting to apply, both will be rejected. If >>> they are mutually true chimers and you don't use prefer, ntpd will use a >>> combination of the time from both of them. >>> >> No, it will choose one and use it until it decides that it is worse than >> another one or they are all declared bad. It never combines both. The >> real problem here is that it has no idea whether or not one is better >> than the other when you only have two of them. > > For RFC 1305, and I have no reason to believe this has changed, given m > servers that pass the basic sanity check, it will start with another > parameter, f, at 0 and try to find m -f intersecting servers. It will > try with successively greater values of f until it finds a mutually > intersecting set of servers. However, if f equals or exceeds m/2, it > will stop with all servers marked as falsetickers. m/2 = 1 in this > case, so the termination condition will be met after one iteration, and > it will fail to find any truechimers (the low end of the range will be > set to the low end of the second server tolerance (search is done > forwards) and the high end of the range will be set to the high end of > the first (search is done backwards).
It has changed. RFC 1305 describes NTPv3. You need to see Section 11.2 of the NTPv4 draft for the current selection algorithms. Particularly: > If the selection > algorithm cannot produce a majority clique, or if it cannot produce > at least CMIN survivors, the system process exits without > disciplining the system clock. If successful, the cluster algorithm > selects the statistically best candidate as the system peer and its > variables are inherited as the system variables. CMIN is currently 1. Notice that it says nothing about using more than one. Danny _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
