Problem Synchronizing NTP from 2600 to Windows XP

Answered Question
Jun 30th, 2010
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I am setting up a closed network for router logging testing purposes and need all devices to have synchronized time via NTP.  I configured an XP box as the authoritative time server with Windows Time Agent and then configured the 2600 routers to point to that IP as the NTP server source.  I let it sit for 24 hours and no synchronization occured.  I read that if the time difference is greater than 4000 seconds (and in this case it was due to the default time a router resets to on reboot) then reset the router clock to a time closer to the NTP server and the sync should occur.  I did that and 24 hours later still no synchronization.  I get the feeling that it has something to do with the fact that my XP box does not connect to an internet stratum 1 or 2 server for it's update that is causing the problem.  Unfortunately, for testing reasons, I can not connect this to any other networks.  Any ideas on how to correct this?

Correct Answer by glen.grant about 6 years 9 months ago

  It seems I read somewhere there is some kind of issue using a windows box as a ntp server .  Maybe this might help you track it down.

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080a23d02.shtml



Basically this is what it says.


Unable to Sync NTP to W32 Based Time Service

When Cisco routers are configured to use the NTP servers placed in  the       Active Directory, the Cisco routers do not receive any NTP packets  from the NTP       server. This issue occurs because Cisco routers use NTP and Active  Directory       domains use W32Time service. W32Time uses Simple Network Time Protocol  (SNTP),       a subset of NTP, for time synchronization. SNTP and NTP use the same       network-packet format. The main difference between SNTP and NTP is  that SNTP       does not provide the error-check and filtering functions that NTP  provides.       Cisco router and switches use NTP and allow for all error-checking and       filtering functions provided by NTP v3.

Windows W32Time shows that it is an SNTP implementation inside  (rather       claiming itself NTP). Cisco IOS-NTP, which tries to sync with W32Time,  gets its       own root-dispersion value that it sends to the W32Time and this proves  costly       for Cisco IOS-NTP to synchronize. Because the root-dispersion value of  Cisco       IOS-NTP goes higher than 1000 ms, it unsynchronizes itself  (clock-select       procedure). Since the Cisco IOS based routers run the full RFC  implementation       of NTP they do not sync to an SNTP server. In this case the output of  the       show        ntp associations detail command shows that the server is       flagged as insane, invalid. The root       dispersion value is in excess of 1000 ms, which causes the Cisco  IOS       NTP implementation to reject the association. Routers that run Cisco  IOS can be       unable to synchronize to an NTP server if it is a Windows system that  runs the       W32Time service. If the server is not synchronized, the routers are  not able to       transmit to and receive packets from the server.

In order to workaround this issue and sync a Cisco IOS based  router,       use an authoritative NTP server on the Internet, a UNIX box that runs  NTPD or a       GPS on certain platforms. As an alternative, you can choose not to run  the       W32Time service on the Windows system. Instead, you can use NTP 4.x.  All       versions of Windows 2000 and later can serve as an NTP server. Other  machines       on the network can then use the NTP server to synchronize their time.

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Correct Answer
glen.grant Wed, 06/30/2010 - 09:48
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  It seems I read somewhere there is some kind of issue using a windows box as a ntp server .  Maybe this might help you track it down.

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080a23d02.shtml



Basically this is what it says.


Unable to Sync NTP to W32 Based Time Service

When Cisco routers are configured to use the NTP servers placed in  the       Active Directory, the Cisco routers do not receive any NTP packets  from the NTP       server. This issue occurs because Cisco routers use NTP and Active  Directory       domains use W32Time service. W32Time uses Simple Network Time Protocol  (SNTP),       a subset of NTP, for time synchronization. SNTP and NTP use the same       network-packet format. The main difference between SNTP and NTP is  that SNTP       does not provide the error-check and filtering functions that NTP  provides.       Cisco router and switches use NTP and allow for all error-checking and       filtering functions provided by NTP v3.

Windows W32Time shows that it is an SNTP implementation inside  (rather       claiming itself NTP). Cisco IOS-NTP, which tries to sync with W32Time,  gets its       own root-dispersion value that it sends to the W32Time and this proves  costly       for Cisco IOS-NTP to synchronize. Because the root-dispersion value of  Cisco       IOS-NTP goes higher than 1000 ms, it unsynchronizes itself  (clock-select       procedure). Since the Cisco IOS based routers run the full RFC  implementation       of NTP they do not sync to an SNTP server. In this case the output of  the       show        ntp associations detail command shows that the server is       flagged as insane, invalid. The root       dispersion value is in excess of 1000 ms, which causes the Cisco  IOS       NTP implementation to reject the association. Routers that run Cisco  IOS can be       unable to synchronize to an NTP server if it is a Windows system that  runs the       W32Time service. If the server is not synchronized, the routers are  not able to       transmit to and receive packets from the server.

In order to workaround this issue and sync a Cisco IOS based  router,       use an authoritative NTP server on the Internet, a UNIX box that runs  NTPD or a       GPS on certain platforms. As an alternative, you can choose not to run  the       W32Time service on the Windows system. Instead, you can use NTP 4.x.  All       versions of Windows 2000 and later can serve as an NTP server. Other  machines       on the network can then use the NTP server to synchronize their time.

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