On Thursday, January 23, 2014 9:36:35 AM UTC+1, Marco Marongiu wrote: > Hi Peter > > > > In your questions, you are showing configuration snippets as they were > > taken from some "authoritative" source. Would you mind sharing that source? > > Hello Marco,
Well, I have come across almost all of the pages, you are mentioning below, but it seems, i have "combined" the info wrongly for my example...:-) > > As for me, I consider the following to be *the* authoritative sources > > for anything NTP: > > > > http://www.eecis.udel.edu/~mills/ntp/html/index.html > > http://doc.ntp.org/ > > http://support.ntp.org > > http://www.ntp.org/ntpfaq/NTP-a-faq.htm > > > > That said, let's see. > > > > On 01/23/2014 08:29 AM, ardi wrote: > > > Below are described some basic cases for ntp.conf on ntp-client: > > > > > > a) > > > In the simplest case of ntp-client the following ntp.conf is defined: > > > > > > restrict default noquery nomodify notrap > > > restrict 127.0.0.1 > > > driftfile /var/lib/ntp/ntp.drift > > > server xx.xx.xx.xx minpoll 4 maxpoll 4 > > > restrict xx.xx.xx.xx > > > > > > Why should i need the restrict line xx.xx.xx.xx? > > > What does the first restrict line means? > > > > First things first: why minpoll and maxpoll? The defaults are generally > > OK -- I had to change that manually only in special cases, and I can > > count them on one hand. > > Does it mean these minpoll, maxpoll parameters are not needed in most of the cases? According to book Expert Network Time Protocol from PETER RYBACZYK: "The minpoll and maxpoll parameters represent minimum and maximum polling intervals for reference clock messages in seconds to the power of 2. For example, if minpoll=3 and maxpoll=4, the minimum polling interval would be 8 seconds, and the maximum polling interval would be 16 seconds." What does "minimum and maximum polling intervals for reference clock messages" mean? polling = messaging with NTP servers to estimate the offset ??? > > Regarding restrict, everything you need to know about noquery, nomodify, > > notrap is here, along with all the information about that directive: > > http://doc.ntp.org/4.2.6p5/accopt.html > > > > If you need some guidance to select the right restrictions that work for > > you, please see > > http://support.ntp.org/bin/view/Support/AccessRestrictions > > > > > > > b1)In case using 2 ntp-servers from which my ntp-client can get time, > > > is my ntp-client taking time from xx.xx.xx.xx > > > and if this server is not reachable then from xx.xx.xx.yy? > > > > First: don't use two servers, it's the worst possible configuration. Why not? what if one of the servers fail? then the client can get time from the other ntp-server. Doesn't the real setup consist of some stratum 1 time servers, then at least two stratum 2 ntp servers which are in peer with each other (and takin time form one or more stratum 1 time servers) and clients are taking time from these stratum 2 servers? see: http://www.ntp.org/ntpfaq/NTP-s-config-adv.htm 6.2.1.3, Figure 5. > > > > The server selection algorithm and why you should use four servers > > whenever possible is sketched here: > > > > http://www.ntp.org/ntpfaq/NTP-s-algo-real.htm#Q-NTP-ALGO > > > > > > > What does prefer do in this case b2)? > > > > See this page, section "The prefer Peer", after reading the reference > > above. In short: if the server marked with "prefer" is selected as a > > survivor, it will be preferred among all other survivors -- it will be > > used when the algorithm would otherwise have selected another server. > > http://doc.ntp.org/4.2.6p5/prefer.html > > > > > > > Is there any difference between b1) and b2) case? > > > > This is left as an exercise to the reader :) > > According to http://doc.ntp.org/4.2.6p5/prefer.html section: The prefer Peer "While the rules do not forbid it, it is usually not useful to designate more than one source as preferred; however, if more than one source is so designated, they are used in the order specified in the configuration file; that is, if the first one becomes unselectable, the second one is considered and so forth." i understand from this that only in case if more than one servers or peers have parameter prefer, then they are used in the order specified in the configuration file; that is, if the first one becomes unselectable, the second one is considered. Is that true? > > > > > b3) > > > what about this case b3) below? > > > Is time taken for the ntp-client according to order of lines - i mean the > > xx.xx.xx.xx is taken as time source? > > > or the 2nd server xx.xx.xx.yy is preferred? > > > > This should be fairly clear now, if you took the time to check the > > references I've mentioned. > > Hmm, server xx.xx.xx.yy minpoll 4 maxpoll 4 prefer will be selected? > > I'd be really curious to check the source of your snippets. Is it a web > > page we can take a peep at? > > > > Ciao! > > -- bronto _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
