Article 7145 of comp.protocols.time.ntp: From: Daniel Wong Newsgroups: comp.protocols.time.ntp Subject: Re: Using NTP on an isolated network which is shut down daily Date: Tue, 15 Sep 1998 14:53:58 -0400 Organization: Lockheed Martin Lines: 71 Distribution: inet Message-ID: <35FEB7C5.4935C221@lmco-NOSPAM.com> References: <01bde0b2$838b8000$8a0211ac@pblust.sensis.com> NNTP-Posting-Host: e7p241.syr.lmco.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 4.05 [en] (WinNT; U) To: Paul Blust Path: news1.meer.net!nntp2.ba.best.com!news1.best.com!su-news-hub1.bbnplanet.com!cpk-news-hub1.bbnplanet.com!cam-news-hub1.bbnplanet.com!news.bbnplanet.com!news.mathworks.com!uunet!uunet!in1.uu.net!newsfeed3.global.lmco.com!news.vf.lmco.com!usenet Xref: news1.meer.net comp.protocols.time.ntp:7145 Paul Blust wrote: > We've got two Sun Ultra workstations running Solaris 2.6 on an isolated > hub. One of the workstations (sun #1) is connected to a GPS receiver; that > sun's clock is synced to GPS time. We'd like to use NTP to synchronize the > other sun (sun #2) to GPS. The accuracy has to be within 1 millisecond. > > The two suns must be powered up and down on a daily basis; leaving them > powered up is not an option. We need to have sun #2 synchronized within 5 > minutes after it is powered up. > > I know that NTP can require "spin-up" time to achieve a certain accuracy, > but we're only talking about two suns on an isolated subnet here; we can > afford a fairly high amount of NTP message traffic. > > Can NTP be configured to meet these specs? Yes it can.My experience is on HP/UX (server and clients) and VxWorks (clients) which allow NTP clients to synchronize to sub-millisecond (verified by Irig-B) over ATM to the NTP server. To meet the fast settling requirement you need to make a few changes in the include/ntp.h file. Some have pointed out that this is "dangerous" but it has worked for us and the NAVY. NUWC and our own testing of NTP recommended the following changes: - change #define NTP_MINPOLL 4 to #define NTP_MINPOLL 1 (this allows polling every 2 seconds) - change #define CLOCK_MAX_FP 000020C5 to 00000290 - change #define CLOCK_MAX_F 20C49BA6 to 02900000 (NTP will step on startup at 10 ms error rather than the default 128 ms) - Change #define CLOCK_WAYTOOBIG 1000 to FFFFFFFF (tells NTP to proceed no matter how far off client is from server) - in /etc/ntp.conf define server with minpoll e.g., server 192.168.20.65 minpoll 1 you can also add a maxpoll to keep the polling period lower for faster settling. The default polling period is a minpoll of 6 which is 2^6 or 64 seconds > If it can, are there > complications from > using NTP this way? Should I break down and buy an IRIG card instead? > make sure that you define a drift file (written once per hour) in your ntp.conf file so that upon reboot, ntp starts with a better estimate of the frequency error. What this means is that you have to let ntp run for a "long while" to get a good drift value. Once you have one, ntp will only take a minute or two to get below 1 ms synchronization with the changes mentioned above. > Thanks for any input, > Paul Blust (Paul.Blust@sensis.com) -- Daniel Wong Principal System Engineer Lockheed Martin Ocean Radar and Sensor Systems Electronics Park EP7-333 Syracuse, NY 13090 (315)456-2162 [FAX (315)456-1430] ------------------------------------------------------------------------ Blessed is the man who always fears the Lord, but he who hardens his heart falls into trouble. -- Proverbs 28:14