# Time Synchronization {{< snippet "old" >}} ## Daylight Saving Time Switch In 2007, the US and Canada, as well as others, changed the rules for when Daylight Saving Time begins and ends. In my opinion this is sheer idiocy, but then, they didn't ask me. Anyway, it really screwed up quite a lot of things, many of which are not in our power to easily fix (GPS, car GPS, VCRs, embedded systems like cheap routers, and much more). Here are some resources: - *[Daylight saving time](http://en.wikipedia.org/wiki/Daylight_saving_time)* from Wikipedia - *[Various](http://ask.slashdot.org/article.pl?sid=06/11/01/2312222)* *[discussions](http://ask.slashdot.org/article.pl?sid=05/07/24/2018201)* on *[Slashdot](http://developers.slashdot.org/article.pl?sid=07/02/16/1646244)* - *[Unofficial Windows 2000 (and 98/ME) Daylight Saving Time Patch](http://www.intelliadmin.com/blog/2007/01/unofficial-windows-2000-daylight.html)* - *[Preparing for daylight saving time changes in 2007](http://www.microsoft.com/dst2007)* - *[2007 time zone update for XP and 2003](http://support.microsoft.com/kb/928388)* - *[tzmove.exe for Outlook/Exchange](http://support.microsoft.com/kb/930879)* - *[How to configure daylight saving time for the United States in 2007](http://support.microsoft.com/kb/914387)* - *[How to change the daylight-saving time program for the new 2004 to 2005 schedule in the Uruguay time zone](http://support.microsoft.com/kb/886775)* - *[Non-MS Preparing for daylight saving time changes in 2007](http://www.calconnect.org/dstlinks.html)* - *[2007 Time Zone Changes Will Impact Many Computers in Canada, the United States and Bermuda](http://www.reganfamily.ca/dst/)* - *[Daylight Saving Chaos during the Commonwealth Games in Australia in 2006](http://stilgherrian.com/internet/daylight-saving-chaos/)* - *[DOS/Windows RTC clock should be set to UTC](http://www.cl.cam.ac.uk/~mgk25/mswish/ut-rtc.html)* ----- ## Importance If time is not consistent across your network 1. *[ISO/IEC 17799:2000(E)](http://www.bspsl.com/17799/)* (AKA BS7799), clause 9.7.3 specifies "Clock synchronization:" "\[...\]Where a computer or communications device has the capability to operate a real-time clock, it should be set to an agreed standard, e.g. Universal Coordinated Time (UCT) or local standard time. As some clocks are known to drift with time, there should be a procedure that checks for and corrects any significant variation." 2. Event Logging, Auditing or Intrusion Detection across different systems becomes very difficult. 3. Many cryptographic functions, especially those involving key creation, exchange and expiration, as well as "ticketing" functions such as used by Kerberos require precise time synchronization. 4. Event or program scheduling may not work as expected. 5. Client/Server transactions may not work as expected (transaction precedence is incorrect). 6. There may be legal issues when submitting logs or other material as evidence if the time is not known to be correct. [^1] 7. Security certificates, WWW Cookies, DHCP and WINS leases may not work as expected. 8. High Availability or clustering solutions may depend on members clocks being exactly synchronized. 9. File creation and access times will be wrong across different computers, thus: 1. Differential, Incremental or other backups may not work as expected. 2. Revision control systems (such as CVS) may not work properly. 3. E-Mail Message time stamps may be wrong, leading to unexpected transmission issues. 10. NetWare NDS will not work right unless all NDS servers have the same time. 11. Neither will Active Directory, even though it says it will. If you have an object collision (two objects are modified at the same time by different people on different masters) the time stamp is used to help resolve the conflict. If time is not synchronized, the results will not be as expected. For more uses or requirements for time synchronization, search the RFCs for other RFCs that specify the use of NTP. [^1]: See *[Securing Windows NT/2000 Servers for the Internet](http://www.oreilly.com/catalog/securwinserv/)* by Stefan Norberg, page 153. ----- ## Time & Time Tips *[Fascinating book review and thread on NTP and time issues at Slashdot](http://books.slashdot.org/books/06/05/15/143251.shtml)*. - *[**Why is UTC used as the acronym for Coordinated Universal Time instead of CUT?**](http://www.boulder.nist.gov/timefreq/general/misc.htm#Anchor-14550)* In 1970 the Coordinated Universal Time system was devised by an international advisory group of technical experts within the International Telecommunication Union (ITU). The ITU felt it was best to designate a single abbreviation for use in all languages in order to minimize confusion. Since unanimous agreement could not be achieved on using either the English word order, CUT, or the French word order, TUC, the acronym UTC was chosen as a compromise. - **Which is correct, UTC or GMT? Does GMT have summer time?** From ** During the Summer the UK is on British Summer Time which is 1 hour ahead of GMT (GMT+1). \[...\] GMT is fixed all year and does not switch to daylight savings time. \[...\] Although GMT has been replaced by atomic time (UTC) it is still widely regarded as the correct time for every international time zone. Greenwich Mean Time is international time, the basis of the world time clock. Marks precision time and military time (sometimes called Zulu Time). \[...\] - **What some critical and significant dates in computing?** See J R Stockton's *[Critical and Significant Dates.](http://www.merlyn.demon.co.uk/critdate.htm)* - **Hey, what time is it anyway?** *[About comp.protocols.time.ntp: life imitates art](http://www.netfunny.com/rhf/jokes/90q3/nettime.html)*. ----- ## Time & Time Zone Links - *[A listing of different "standard" times](http://www.leapsecond.com/java/gpsclock.htm)*, and why they are not all the same. - Information about different *[Systems of Time](http://tycho.usno.navy.mil/systime.html)*. - **A Summary of the International Standard Date and Time Notation *[ISO8601](http://www.cl.cam.ac.uk/~mgk25/iso-time.html)*.** - *[**Download a Copy of the ISO 8601 Standard**](http://www.qsl.net/g1smd/isopdf.htm)* - *[w3c: Date and Time Formats](http://www.w3.org/TR/NOTE-datetime)* - *[U.S. Naval Observatory World Time Zone Map](http://aa.usno.navy.mil/AA/faq/docs/world_tzones.html)* - *[Set Your Computer Clock to NIST Time](http://www.bldrdoc.gov/timefreq/service/time-computer.html)* - *[ISO Time Displayed](http://greenwichmeantime.com/info/iso.htm)* - *[TimeZone Table](http://greenwichmeantime.com/info/time-zones.htm)* - *[Sources for Time Zone and Daylight Saving Time Data](http://www.twinsun.com/tz/tz-link.htm)* - *[World TimeZone Map](http://aa.usno.navy.mil/AA/faq/docs/world_tzones.html)* - *[Info about GMT/UTC, etc.](http://greenwichmeantime.com/)* - *[A World Time Clock](http://www.timeanddate.com/worldclock/)* - *[Perl/CGI Time Zone Converter](http://sandbox.xerox.com/stewart/tzconvert.cgi)* - *[The Yahoo Time Directory](http://dir.yahoo.com/Science/Measurements_and_Units/Time/Current_Time/)* - *[Excel: Using Dates and Times (XE0127) Complete Text](http://support.microsoft.com/support/kb/articles/Q95/9/48.asp)* - *[A Graphical World Time Map/Clock](http://www.maps.com/reference/thematic/timeclock/)* - *[Minimalist FREE Time Zone Clock Software](http://members.surfeu.fi/antti.kurenniemi/)* - *[FREE Time Zone Clock Software](http://www.mirage1.u-net.com/clox.htm)* - *[FREE Time Zone Clock Software](http://www.pdabusiness.com/qlock/)* - *[FREE Time Zone Clock Software](http://www.cimmyt.org/timezone/index.htm)* - *[The ID LOGIC World Time Clock](http://www.classicalarchives.com/prs/wt.html)* - *[Time Zone software for PC](http://www.timezonesforpcs.com/details.htm)* - *[Sells all kinds of clock products, including auto-sync "slave" clocks\!](http://www.brgprecision.com/)* ----- ## NTP Links - The definitive book: *[Computer Network Time Synchronization: the Network Time Protocol](http://www.cis.udel.edu/~mills/book.html)* - See also *[a fascinating book review and thread on NTP and time issues at Slashdot](http://books.slashdot.org/books/06/05/15/143251.shtml)* - Another book: *[Expert Network Time Protocol: An Experience in Time with NTP](http://www.apress.com/book/bookDisplay.html?bID=429)* - Then read *[public NTP time servers for everyone](http://www.pool.ntp.org/)* and *[the NTP Pool for vendors](http://www.pool.ntp.org/vendors.html)*. Don't be idiots like *[Netgear](http://www.cs.wisc.edu/~plonka/netgear-sntp/)* and *[D-Link](http://yro.slashdot.org/article.pl?sid=06/04/07/130209)* were. - The following articles from Sun are an excellent introduction to NTP concepts and implementation, while from a Solaris perspective, they are probably useful to anyone interested in time synchronization. - *[**Introduction to NTP (July 2001)**](http://www.sun.com/blueprints/0701/NTP.pdf)* \[PDF\] - *[Basic NTP Administration and Architecture (August 2001)](http://www.sun.com/blueprints/0801/NTPpt2.pdf)* \[PDF\] - *[NTP Monitoring and Troubleshooting (September 2001)](http://www.sun.com/blueprints/0901/NTPpt3.pdf)* \[PDF\] - The "*[Time WWW server](http://www.ntp.org/index.html)*" page. Official page of NTP and **the** source of time and NTP information. - *[Quick start for NTP](http://www.eecis.udel.edu/~mills/ntp/html/quick.html)* - *[Configuring xntp](http://www.eecis.udel.edu/~ntp/ntpfaq/NTP-s-config.htm)* - *[Configuring Clients and Servers](http://www.eecis.udel.edu/~mills/ntp/html/index.html)* - *[The NTP FAQ](http://www.ntp.org/ntpfaq/NTP-a-faq.htm)* - *[Notes on Configuring NTP and Setting up a NTP Subnet](http://www.eecis.udel.edu/~mills/ntp/html/notes.html)* - *[Doug Hogarth's Niceties](http://www.niceties.com/index.html)* site. - [A list of Windows Time Sync Tools](/public/TimeSync.xls) (in Excel format, originally researched by me in 1999 and 2000, last updated May 2003 by Jason Mathews \) ----- ## Time Synchronization Tools ### NTP Tools for Windows - First read *[public NTP time servers for everyone](http://www.pool.ntp.org/)* and *[the NTP Pool for vendors](http://www.pool.ntp.org/vendors.html)*. - By far the best NTP client and server that I found is *[Tardis](http://www.kaska.demon.co.uk/)*. It runs as an NTP client and NTP server. There is one version that is an NT4/Win2K service, and another that runs as a normal application under Win9x/ME. It has only one minor problem -- it's not free. It runs from $20 to $2,000 USD, see the *[web site](http://www.kaska.demon.co.uk/howtopay.htm)* for details. - The next best is the *["official" NTP](http://www.ntp.org/downloads.html)* package from David Mills. Only the source is available from the Time Server site, but compiled binaries for Windows are available. - *[ntp4172.zip](http://www.five-ten-sg.com/util/ntp4172.zip)* is available from *[510 Software Group](http://www.five-ten-sg.com/)*. This package includes a GUI setup.exe installation routine. - There is also a *[Windows NT port](http://norloff.org/ntp/)* Maintained by Terje Mathisen. - NTP for Windows NT/2000/XP/2003/Vista is an *[NTP for Windows](http://www.meinberg.de/english/sw/ntp.htm)* binary port and installer, along with a cool *[monitoring GUI](http://www.meinberg.de/english/sw/time-server-monitor.htm)*. - If you own the *[NT Resource Kit](http://www.microsoft.com/TechNet/winnt/Winntas/tools/nt4sp4rk.asp)* (or a newer ResKit), you should look into the NTRK TimeServ utility. While you can only get the TimeServ tool from the NTRK, you can find more information about it, and time in general at *[Doug Hogarth's Niceties](http://www.niceties.com/index.html)* site, specifically the *[TimeServ](http://www.niceties.com/TimeServ.html)* page. Also see other built-in Windows options below. - Tom Horsley's *[NTP Time](http://home.att.net/~Tom.Horsley/ntptime.html)* for Windows is a nice NTP client program. It is free, but is a client only, and can be configured to talk to only one NTP server at a time. NTP works much better when referencing a pool of servers. - I have also used the very cool *[AboutTime](http://www.arachnoid.com/abouttime/index.html)* program, which is a Daytime/TCP, Time/TCP, Time/UDP and SNTP client and server. It runs under any Windows version, but does not run as a service. It is **free**\! - I've used *[Dimension4](http://www.thinkman.com/dimension4/index.html)*, which is a free client for Time and NTP. - There are also *[Tardis/K9](http://www.kaska.demon.co.uk/)*, which are excellent shareware tools. - And for a minimalistic web site but neat sounding tool, see Graham Mainwaring's *[NetTime](http://nettime.sourceforge.net/)*, at Sourceforge. #### The Microsoft Networking "Net Time" Command Displays the time on or synchronizes your computer's clock with the shared clock on a Microsoft Windows for Workgroups, Windows NT, Windows 95, or NetWare time server. ``` NET TIME [\\computer | /WORKGROUP:wgname] [/SET] [/YES] computer Specifies the name of the computer (time server) whose time you want to check or synchronize your computer's clock with. /WORKGROUP Specifies that you want to use the clock on a computer (time server) in another workgroup. wgname Specifies the name of the workgroup containing a computer whose clock you want to check or synchronize your computer's clock with. If there are multiple time servers in that workgroup, NET TIME uses the first one it finds. /SET Synchronizes your computer's clock with the clock on the computer or workgroup you specify. /YES Carries out the NET TIME command without first prompting you to provide information or confirm actions. ``` For example, if your PCD is named MYPDC, the following command in a shortcut in your Startup Group, or in a logon script will synchronize a client PC's time at logon. Note, if your clients never log off, this will not work. Of course, that's very bad for other reasons. This works for any system that runs Microsoft Networking. You can even sync again a Linux server running *[Samba](http://www.samba.org/)* with this command, if you'd like\! > "net time \\\\MYPDC /set/ yes" #### Win2K NTP Time Service Win2K has a very simple SNTP facility built in: "net time /setsntp\[:NTP server list\]". See the following for more information: - First read *[public NTP time servers for everyone](http://www.pool.ntp.org/)* and *[the NTP Pool for vendors](http://www.pool.ntp.org/vendors.html)*. - *[Win32 Time Service Informational, Warning, and Error Messages \[Q232209\]](http://support.microsoft.com/support/kb/articles/Q232/2/09.asp)* - *[How to Configure an Authoritative Time Server in Windows 2000 \[Q216734\]](http://support.microsoft.com/support/kb/articles/Q216/7/34.asp)* - *[Registry Entries for the W32Time Service \[Q223184\]](http://support.microsoft.com/support/kb/articles/Q223/1/84.asp)* - *["Could Not Locate a Time Server" After Setting SNTP Time Server \[Q243574\]](http://support.microsoft.com/support/kb/articles/Q243/5/74.asp)* Here is the batch file I use, since I find the documentation lacking and the usage statement obscure: ```batch @echo off REM Win2k-SNTP.bat -- Set Win2K SNTP service REM v1.0 25-May-2001 JP Vossen {{< snippet "contact" >}} REM v1.1 22-Jun-2001 JPV Changed to use home NTP time source only rem NOTE: The Win2K "Windows Time" service is manual by default, so you have to rem set it to automatic and start it. Also, it will attempt to use all specified rem time sources and get an "average" so only specify servers that will be rem available at all times. Do not use the list as a set of sequential rem "failover" servers (as I did in v1.0 of this). rem NET TIME /SETSNTP:"192.168.1.11 172.16.1.1 10.1.1. 10.1.1.2" NET TIME /SETSNTP:"192.168.1.11" ``` You can see how it's currently set by using this command: "net time /querysntp" which will return something like: ``` The current SNTP value is: 192.168.1.11 The command completed successfully. ``` ### NTP Tools for Netware #### For a small network with one or more NetWare servers, but no WAN links or remote sites: 1. First read *[public NTP time servers for everyone](http://www.pool.ntp.org/)* and *[the NTP Pool for vendors](http://www.pool.ntp.org/vendors.html)*, don't use the ones listed in TID 10011518. 2. Set one NetWare server as the SINGLE Reference server. This server will sync itself to the NTP time. - Load MONITOR.NLM | Server Parameters | Time, change the following parameters - Default Time Server Type = SINGLE - TIMESYNC Configured Sources = ON - TIMESYNC Time Sources = \<2-4 NTP time sources\>:123; Where 123 is the NTP port on that time source. - Example: TIMESYNC Time Sources = 172.31.1.1:123;172.31.2.1:123;172.31.3.1:123; 3. Set **any/all** other NetWare servers as SECONDARY. #### For a small network with more than one NetWare server, and with WAN links or remote sites: 1. First read *[public NTP time servers for everyone](http://www.pool.ntp.org/)* and *[the NTP Pool for vendors](http://www.pool.ntp.org/vendors.html)*, don't use the ones listed in TID 10011518. 2. Set one NetWare server as the REFERENCE server. This server will sync itself to the NTP time. - Load MONITOR.NLM | Server Parameters | Time, change the following parameters - Default Time Server Type = REFERENCE - Time Server Type = REFERENCE - TIMESYNC Configured Sources = ON - TIMESYNC Time Sources = \;\<2-4 NTP time sources\>:123; 3. Set one other NetWare server at the main site, and one NetWare server at each remote site as a PRIMARY server. - Load MONITOR.NLM | Server Parameters | Time, change the following parameters - Default Time Server Type = PRIMARY - Time Server Type = PRIMARY - TIMESYNC Configured Sources = ON - TIMESYNC Time Sources = \; 4. Set **all** other NetWare servers as SECONDARY. - Load MONITOR.NLM | Server Parameters | Time, change the following parameters - Default Time Server Type = SECONDARY - Time Server Type = SECONDARY - TIMESYNC Configured Sources = ON - TIMESYNC Time Sources = \; Note: usually, the REFERENCE server does not ever change it's own time, it just serves the time. However, when using NTP, the REFERENCE server will adjust its local clock to synchronize with the NTP time source. See the middle of TID *[10050215](http://support.novell.com/cgi-bin/search/tidfinder.cgi?10050215)*. - **TID *[10020147](http://support.novell.com/cgi-bin/search/tidfinder.cgi?10020147)*: Time Synchronization White Paper** - **TID *[10011518](http://support.novell.com/cgi-bin/search/tidfinder.cgi?10011518)*: Configuring an External NTP Source with NW 5** - **TID *[10050215](http://support.novell.com/cgi-bin/search/tidfinder.cgi?10050215)*: Timesync Frequently Asked Questions** - **TID *[10011517](http://support.novell.com/cgi-bin/search/tidfinder.cgi?10011517)* (Formerly TID *[2908867](http://support.novell.com/cgi-bin/search/tidfinder.cgi?2908867)* Part 3): TIMESYNC SET Parameters Reference** - TID *[2955431](http://support.novell.com/cgi-bin/search/tidfinder.cgi?2955431)*: "Timesync Type" vs "Default Timesync Type". - *[Using Network Time Protocol (NTP) with NetWare 5](http://developer.novell.com/research/appnotes/1999/july/03/index.htm)* - *[Understanding NetWare Time Synchronization](http://www.novell.com/documentation/lg/nw5/docui/index.html)* - TID *[10016021](http://support.novell.com/cgi-bin/search/tidfinder.cgi?10016021)* (formerly TID 2932671): External timesync sources - web site for NetWare servers not using v5 or better. Thanks to Steve Schrank & Bob Kulp for some of these Netware pointers. ### NTP Tools for UNIX - First read *[public NTP time servers for everyone](http://www.pool.ntp.org/)* and *[the NTP Pool for vendors](http://www.pool.ntp.org/vendors.html)*. - Use xNTPd, or whatever came with your UNIX system. - For Linux, use whatever xNTP package comes with your system. Avoid "time," "daytime," etc. - For Solaris, use SUNWntpr & SUNWntpu, or get the NTP package from *[Sunfreeware.com](http://www.sunfreeware.com/)*. Here is a very minimalist sample [ntp.conf](/public/source/Solaris-etc-ntp.conf.txt) and [startup script](/public/source/Solaris-etc-rc2.d-S98ntp.txt) (minor modifications to **. - For HPUX use SAM to configure the NTP facility. See the following articles as well. They are Sun centric, but still relevant for other UNIX systems: - *[**Introduction to NTP (July 2001)**](http://www.sun.com/blueprints/0701/NTP.pdf)* - *[Basic NTP Administration and Architecture (August 2001)](http://www.sun.com/blueprints/0801/NTPpt2.pdf)* - *[NTP Monitoring and Troubleshooting (September 2001)](http://www.sun.com/blueprints/0901/NTPpt3.pdf)* ### NTP for Cisco IOS Thanks to [Greg Sottile](mailto:gsottile@bellatlantic.net) for this section on IOS. - SNTP does not support server mode. In order for the router to act as a master, it must be capable of running as a server. - - First read *[public NTP time servers for everyone](http://www.pool.ntp.org/)* and *[the NTP Pool for vendors](http://www.pool.ntp.org/vendors.html)*. With that said, the commands are the following: | IOS Commands | Description | | ------------------------------------------------- | ---------------------------------------------------------------------------- | | clock timezone est -5 | Set your correct time zone. | | clock summer-time edt recurring | Set daylight savings. | | ntp master 6 | Become an NTP server. | | ntp update-calendar | Periodically set calendar from an NTP server. Supported by 7000, 7200, 4500. | | ntp server {insert your favorite NTP server here} | NTP server from which to get the time | ### NTP for Nokia IPSO IPSO comes with xNTP, but you can't change the default polling, which is something like every minute and a half. Until Voyager is enhanced to provide this capability, there is no easy way to do it. You could edit the ntp.conf file, but Voyager will overwrite it at bootup. [S50fixntp.sh](/public/source/S50fixntp.txt) is a script I got from Nokia support database resolution 3808 (Thanks Dameon), with minor modifications and additional documentation. Read the code for more details. Then read *[public NTP time servers for everyone](http://www.pool.ntp.org/)* and *[the NTP Pool for vendors](http://www.pool.ntp.org/vendors.html)*. ### Other Lists of Time Client and/or Server Programs - [A list of Windows Time Sync Tools](/public/TimeSync.xls) (in Excel format, originally researched by me in 1999 and 2000, last updated May 2003 by Jason Mathews \) - ** - *[http://www.niceties.com/TimeServ.html\#FAQ](http://www.niceties.com/TimeServ.html)* ----- ## Time Protocols | Port | Name | Description/Accuracy | Source | | ----------- | ---------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------ | | 13 tcp/udp | Daytime | Returns the day and time in an ASCII string. No accounting for different time zones, daylight savings, etc. Very inaccurate. | *[RFC867](http://www.faqs.org/rfcs/rfc867.html)* | | 37 tcp/udp | Timeserver | Returns the number of seconds since 00:00 (midnight) 1 January 1900 GMT, such that the time 1 is 2:00:01 am on 1 January 1900 GMT. No accounting for different time zones, daylight savings, etc. Very inaccurate. | *[RFC868](http://www.faqs.org/rfcs/rfc868.html)* | | 52 tcp/udp | Xns-time | Xerox Time | (*[RFC1700](http://www.faqs.org/rfcs/rfc1700.html)*) | | 123 tcp/udp | NTP/SNTP | NTP (Network Time Protocol) or SNTP (Simple Network Time Protocol). Accurate to the limitations of the clock hardware. | *[RFC1305](http://www.faqs.org/rfcs/rfc1305.html)*, *[RFC2030](http://www.faqs.org/rfcs/rfc2030.html)* | | 309 | EntrusTime | ??? Entrust Time protocol ??? | *[GnatBox Admin Tool](http://www.gta.com/)* | | 519 tcp/udp | unixtime | utime | (*[RFC1700](http://www.faqs.org/rfcs/rfc1700.html)*) | | 525 tcp/udp | Timeserver | Timed | (*[RFC1700](http://www.faqs.org/rfcs/rfc1700.html)*) | | 1506 | Utcd | UTC (Universal Time Coordinated, AKA GMT, AKA Zulu) daemon | *[GnatBox Admin Tool](http://www.gta.com/)* | Notes: 1. Protocols marked with (*[RFC1700](http://www.faqs.org/rfcs/rfc1700.html)*) are listed, but not defined in the RFC. 2. Protocols marked with *[GnatBox Admin Tool](http://www.gta.com/)* are listed in the services list in the executable. {{< snippet "old" >}}