<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: arial,helvetica,sans-serif; font-size: 10pt; color: #000000'>What about GPS, GLONASS, Galileo, etc.?<br><br><div><span name="x"></span><br><br>-----<br>Mike Hammett<br>Intelligent Computing Solutions<br>http://www.ics-il.com<br><br>Midwest-IX<br>http://www.midwest-ix.com<span name="x"></span><br></div><br><hr id="zwchr"><div style="color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>From: </b>"James R Cutler" <james.cutler@consultant.com><br><b>To: </b>"Harlan Stenn" <stenn@nwtime.org><br><b>Cc: </b>nanog@nanog.org<br><b>Sent: </b>Wednesday, May 1, 2019 8:55:51 PM<br><b>Subject: </b>Re: NTP question<br><br><div><blockquote class=""><div class="">On May 1, 2019, at 9:45 PM, Harlan Stenn <<a href="mailto:stenn@nwtime.org" class="" target="_blank">stenn@nwtime.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><br class=""><br class="">On 5/1/19 5:39 PM, William Herrin wrote:<br class=""><blockquote class="">On Wed, May 1, 2019 at 12:23 PM Mehmet Akcin <<a href="mailto:mehmet@akcin.net" class="" target="_blank">mehmet@akcin.net</a>> wrote:<br class=""><br class=""><blockquote class="">I am trying to buy a GPS based NTP server like this one<br class=""><br class=""><a href="https://timemachinescorp.com/product/gps-time-server-tm1000a/" class="" target="_blank">https://timemachinescorp.com/product/gps-time-server-tm1000a/</a><br class=""><br class="">but I will be placing this inside a data center, do these need an actual<br class="">view of a sky to be able to get signal or will they work fine inside a data<br class="">center building? if you have any other hardware requirements to be able to<br class="">provide stable time service for hundreds of customers, please let me know.<br class=""><br class=""></blockquote><br class="">You buy a powered GPS antenna for it. Which antenna depends on the cable<br class="">length and type. The amplifier in the antenna amplifies the signal just<br class="">enough to overcome the cable loss between the antenna and the receiver.<br class="">Nice thick cables lose less signal. Dinky thin ones are easier to work with.<br class=""><br class="">You sure you need a GPS NTP server? You understand that if you do, you need<br class="">two for reliability right, and probably at geographically diverse<br class="">locations? If you're not on an air-gapped network, consider syncing a<br class="">couple head-end NTP servers against tick and tock (.usno.navy.mil, the<br class="">naval observatory) and not worrying about it. One less piece of equipment<br class="">to manage, update, secure, etc.<br class=""></blockquote><br class="">Two is not a great number. If they disagree, there is no majority<br class="">clique to be found.<br class=""><br class="">Also, there is something to be said for using different models/vendors<br class="">for the time sources. If you only have the same model from one vendor<br class="">and there is a bug, you can lose all your time sources at once. The<br class="">GPS week rollover happens every ~19.7 years, and when that problem hits<br class="">is a function of the firmware and a manufacturing date put in the firmware.<br class=""><br class="">These problems can be mitigated if you have "enough" time sources for<br class="">your internal NTP servers and you peer with enough other, possibly your,<br class="">servers.<br class=""><br class=""><blockquote class="">Regards,<br class="">Bill Herrin<br class=""></blockquote><br class="">-- <br class="">Harlan Stenn <<a href="mailto:stenn@nwtime.org" class="" target="_blank">stenn@nwtime.org</a>><br class=""><a href="http://networktimefoundation.org" class="" target="_blank">http://networktimefoundation.org</a> - be a member!<br class=""></div></div></blockquote></div><br class=""><div class=""><div class="">To amplify the points made by Harlan Stenn:</div><div class=""><br class=""></div><div class="">Four is a better number locally for ntpd instances. As for different models/vendors for the time sources, I consider the GPS constellation as one vendor so I add multiple internet-connected sources as well to my ntp.conf instances.</div><div class=""><br class="webkit-block-placeholder"></div><div class=""><br class="webkit-block-placeholder"></div><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><span class="Apple-style-span" style="border-collapse: separate; font-variant-ligatures: normal; font-variant-east-asian: normal; font-variant-position: normal; line-height: normal; border-spacing: 0px; -webkit-text-decorations-in-effect: none;"><span class="Apple-style-span" style="border-collapse: separate; font-variant-ligatures: normal; font-variant-east-asian: normal; font-variant-position: normal; line-height: normal; border-spacing: 0px; -webkit-text-decorations-in-effect: none;"><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px; font-size: 12px; font-variant-ligatures: normal; font-variant-east-asian: normal; font-variant-position: normal; line-height: normal; -webkit-text-decorations-in-effect: none;"><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px; font-variant-ligatures: normal; font-variant-east-asian: normal; font-variant-position: normal; line-height: normal; -webkit-text-decorations-in-effect: none;"><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px; font-variant-ligatures: normal; font-variant-east-asian: normal; font-variant-position: normal; line-height: normal; -webkit-text-decorations-in-effect: none;"><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">James R. Cutler</div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><a href="mailto:James.cutler@consultant.com" class="" target="_blank">James.cutler@consultant.com</a></div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">GPG keys: <a class="">hkps://hkps.pool.sks-keyservers.net</a></div></div></span></span></span></span></span></div></div></div></div><div><br class=""><blockquote class=""></blockquote></div></div></div><br></div></body></html>