Differences

This shows you the differences between two versions of the page.

--- networking:ntp [2021/03/10 02:50] – [Burst and iBurst] bstafford
+++ networking:ntp [2021/09/23 10:23] (current) – removed bstafford
@@ Line 1: / Line 1: @@
-====== NTP ======
-It is best to use **pool.ntp.org** as an NTP server. This will find the closest available servers for you.
-Also
-  * pool.ntp.org
-  * 0.pool.ntp.org
-  * 1.pool.ntp.org
-  * 2.pool.ntp.org
-  * 3.pool.ntp.org
-More specific are:
-  * ntp0.ja.net (Stratum 1)
-  * ntp1.npl.co.uk (Stratum 2)
-  * time.cloudflare.com (Stratum 3)
-  * uk.pool.ntp.org
-  * 0.uk.pool.ntp.org
-  * 1.uk.pool.ntp.org
-  * 2.uk.pool.ntp.org
-  * 3.uk.pool.ntp.org
-  * europe.pool.ntp.org
-  * 0.europe.pool.ntp.org
-  * 1.europe.pool.ntp.org
-  * 2.europe.pool.ntp.org
-  * 3.europe.pool.ntp.org
-The 0, 1, 2 and 3.pool.ntp.org names point to a random set of servers that will change every hour.
-===== Testing Windows NTP =====
-You can test NTP manually using Windows using the following command (where 192.168.1.1 is the IP of the NTP server).
-<code>w32tm /stripchart /dataonly /computer:192.168.1.1</code>
-Resynchronize the clock
-<code>w32tm /resync</code>
-Show current timezone settings
-<code>w32tm /tz</code>
-List external NTP servers (peers)
-<code>w32tm /query /peers</code>
-**REMEMBER** It is important to note that W32Time will only actively synchronize with one time source at a time, even though you are able to list more than one time source. ([[https://docs.microsoft.com/en-gb/archive/blogs/w32time/configuring-the-time-service-ntpserver-and-specialpollinterval|source]])
-Most NTP implementations would poll all the servers to choose the best sample, but as of Server 2008, Windows doesn't. That may have changed since then, but it isn't very documented.
-<code>w32tm /config /manualpeerlist:0.nl.pool.ntp.org,1.nl.pool.ntp.org,2.nl.pool.ntp.org,3.nl.pool.ntp.org,0x1 /syncfromflags:MANUAL /reliable:yes /update ; net stop w32time ; net start w32time ; w32tm /query /peers /verbose</code>
-<code>w32tm /config /manualpeerlist:time.cloudflare.com,0x1 /syncfromflags:MANUAL /reliable:yes /update ; net stop w32time ; net start w32time ; w32tm /query /peers /verbose</code>
-===== Set Linux Time =====
-<code>sudo date -s "22 JUN 2020 13:11:30"</code>
-===== Check Status =====
-Check status of NTP on Ubuntu 16.04+
-<code>timedatectl status</code>
-If NTP is not on, try the following command
-<code>sudo timedatectl set-ntp on</code>
-===== NTP Servers =====
-List of Stratum 1 servers
-  * [[http://tf.nist.gov/tf-cgi/servers.cgi|NIST]]
-  * [[http://support.ntp.org/bin/view/Servers/StratumOneTimeServers|ntp.org]]
-National Physics Laboratory hosts two public "Stratum 2" servers. This means their servers sync directly to atomic clocks.
-**DO NOT** configure your system to use Google Public NTP together with non-leap-smearing NTP servers. e.g. do not combine Google NTP with Cloudflare NTP as they [[https://developers.cloudflare.com/time-services/ntp/usage|do not implement leap smearing]]. Smearing is used by Google, AWS, and Facebook NTP servers but not Cloudflare.
-^Operator ^ Server FQDN ^ Server IP ^ Stratum ^ RefID ^ Source Type or FQDN ^ Delay ^ Location ^ Supports iBurst ^
-| Cloudflare | time.cloudflare.com | 162.159.200.1 | 3 | 10.21.8.19 | Internal Cloudflare? | 13.080 | UK | |
-| Cloudflare | time.cloudflare.com | 162.159.200.123 | 3 | 10.21.8.19 | Internal Cloudflare? | 13.896 | UK | |
-| Microsoft | time.windows.com | 51.145.123.29 | 3 | 25.66.230.5 | Internal Microsoft? | 13.896 | UK | |
-| Zen Internet | ntp0.zen.co.uk | 212.23.8.6 | 2 | 195.66.241.3 | ntp1.linx.net | 11.642 |  | |
-| Zen Internet | ntp1.zen.co.uk | 212.23.10.129 | 2 | 85.199.214.99 | server1.quickdrivingtestcancellations.net | 16.948 | UK | |
-| National Physics Laboratory | ntp1.npl.co.uk | 139.143.5.30 | 2 | 139.143.45.169 | ? | 16.457 | UK | |
-| National Physics Laboratory | ntp2.npl.co.uk | 139.143.5.31 | 2 | 139.143.45.169 | ? | 17.329 | UK | |
-| Manchester University | ntp2a.mcc.ac.uk | 130.88.202.49 | 2 | 193.62.22.66 | ntp0.ja.net | 22.581 | UK | |
-| Manchester University | ntp2b.mcc.ac.uk | 130.88.203.13 | 2 | 130.88.203.13 | ntp0.ja.net | 22.282 | UK | |
-| Manchester University | ntp2c.mcc.ac.uk | 130.88.200.6 | 2 | 193.62.22.66 | ntp0.ja.net | 22.135 | UK | |
-| Manchester University | ntp2d.mcc.ac.uk | 130.88.212.143 | 2 | 193.62.22.74 | ntp1.ja.net | 22.771 | UK | |
-| JANET, Harwell | ntp0.ja.net | 193.62.22.66 | 1 | .MSF. | MSF Radio Clock Receiver | 15.981 | UK | |
-| JANET, Harwell | ntp1.ja.net | 193.62.22.74 | 1 | .MRS. | N/A | 26.042 | UK | |
-| JANET, Harwell | ntp2.ja.net | 193.62.22.98 | 2 | 193.62.22.74 | ntp1.ja.net | 22.849 | UK | |
-| JANET, Harwell | ntp3.ja.net | 193.62.22.90 | 1 | .PPS. | N/A | 26.305 | UK | |
-| JANET, Harwell | ntp4.ja.net | 193.62.22.82 | 1 | .DCFa. | DCF77 | 17.528 | UK | |
-| Google | time.google.com | time1-time4  | 1 |  |  |  | | Yes |
-| Google | time1.google.com | 216.239.35.0  | 1 | .GOOG. | N/A | 20.393 | | Yes |
-| Google | time2.google.com | 216.239.35.4 | 1 | .GOOG. | N/A | 20.399 | | Yes |
-| Google | time3.google.com | 216.239.35.8 | 1 | .GOOG. | N/A | 20.514 | | Yes |
-| Google | time4.google.com | 216.239.35.12 | 1 | .GOOG. | N/A | 22.899 | | Yes |
-| Facebook | time.facebook.com | time1-time5  | 1 |  |  |  | | Yes |
-| Facebook | time1.facebook.com | 129.134.28.123 | 1 | .FB... | N/A | 25.595 | | Yes |
-| Facebook | time2.facebook.com | 129.134.29.123 | 1 | .FB... | N/A | 16.803 | | Yes |
-| Facebook | time3.facebook.com | 129.134.25.123 | 1 | .FB... | N/A | 12.037 | | Yes |
-| Facebook | time4.facebook.com | 129.134.26.123 | 1 | .FB... | N/A | 18.341 | | Yes |
-| Facebook | time5.facebook.com | 129.134.27.123 | 1 | .FB... | N/A | 16.546 | | Yes |
-| Apple | time.apple.com | 17.253.108.253 (and others)  | 1 | .SHM. |  | 17.343 | | Yes |
-| Apple | time.euro.apple.com | 17.253.34.125 (and others) | 1 | .SHM. |  |  9.889 | | Yes |
-| Leo Bodnar Electronics | ntp1.leontp.com | 51.155.16.62 | 1 | .GPS. | N/A | 36.932 | UK | |
-| Leo Bodnar Electronics | ntp5.leontp.com | 85.199.214.98 | 1 | .GPS. | N/A | 16.523 | UK | |
-| Leo Bodnar Electronics | ntp6.leontp.com | 85.199.214.99  | 1 | .GPS. | N/A | 15.949 | UK | |
-| Leo Bodnar Electronics | ntp7.leontp.com | 85.199.214.100 | 1 | .GPS. | N/A | 16.002 | UK | |
-| Leo Bodnar Electronics | ntp8.leontp.com | 85.199.214.101 | 1 | .GPS. | N/A | 16.595 | UK | |
-| Leo Bodnar Electronics | ntp9.leontp.com | 85.199.214.102 | 1 | .GPS. | N/A | 15.965 | UK | |
-| Xentex IT Solutions | ntp.xtx.cloud | 81.133.66.177 | 1 | .PPS. | N/A | 24.301 | UK | |
-More information on Google's NTP offering can be found [[https://developers.google.com/time/faq|here]]. Google 'smear' a leap second over the course of a the hour either side of the leap second. Do not mix NTP servers that 'smear' and NTP servers that do not 'smear'.
-Google uses its own NTP servers (see above) for its public DNS servers (see below). If you cannot configure multiple servers, ''time.google.com'' will automatically select an appropriate Google server nearby.
-===== Timezones =====
-  * [[https://www.iana.org/time-zones|IANA's page on timezones]]
-  * [[https://en.wikipedia.org/wiki/List_of_tz_database_time_zones|List of Timezones]]
-  * [[https://en.wikipedia.org/wiki/List_of_time_zone_abbreviations|List of Timezone Abbreviations]]
-===== Burst and iBurst =====
-Using the burst option against a public server is considered abuse. Do not use this option with public NTP servers. Use it only for applications within your own organization.
-Burst and iBurst are only relevant if the NTP Servers you are synchronising to actually support these features, if not they can be switched off.
-The 'burst' option is used to increase the average quality of time offset statistics. At every poll interval, when the NTP server responds, the system will send a burst of up to eight packets instead of the usual one packet. For use with the server command to improve the average quality of the time-offset calculations as well as accurately measure jitter with long poll intervals.
-The 'iburst' option is used to improve the time taken for initial synchronization. When the NTP server is unreachable, the NTP client sends a burst of eight packets instead of the usual one packet and then shorten the time until the first sync. The packet spacing is normally 2 seconds. The iburst mode continues to send frequent NTP queries until the server responds and time synchronization starts. After the first minute, the iburst mode typically synchronizes the clock so that queries need to be sent at intervals of 64 seconds or more.
-Microsoft only support Simple Network Time Protocol (sntp) which is compatible with NTP clients but does not offer all the functionality of NTP (including Burst and iBurst). Microsoft servers will just ignore the burst and iburst options.