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Tech Tip: CUCM unable to synch time with Windows 2000 NTP server

Hi All,

There is a bug for this condition, sometimes when you use a Windows based NTP the time is not accurate.

NTP unable to sync time with Windows time server


Entering a Windows-based Time Service as an external Network Time Protocol (NTP) server results in NTP failure
on publisher.


Customer has Windows Time Service using Nt5DS or Simple Network Time Protocol (SNTP) set up on a Windows machine
and enters this machine's DNS name or IP address into the external NTP server list.  Post-install will fail
indicating that the external NTP server is unreachable.

Note that NTP and SNTP are different protocols and cannot be mixed.


The windows machine must be configured to use and serve NTP-based time synchronization.

<B>Further Problem Description:</B>

In Cisco Unified CallManager it is possible to have the cluster's time syncrhronized with a very accurate time
source or to use the primary node's system clock.  Relying on a system clock is subject to drift and can be especially
problematic if the system battery had died and a reboot occurs as the system clock could be way off.  If the
cluster is to synchronize with an external time source, it is necessary to configure the publisher to access a
server running Network Time Protocol (NTP).  Note that the external time source MUST NOT be Simple Network Time
Protocol (SNTP) as is commonly used in Microsoft Windows environments.

A Windows machine can be configured to to use NTP by setting a registry setting.

Note: To modify entries in the Windows 2000 registry, you must be a member of the Administrators group on the local
computer, or you must have been delegated the appropriate authority. If the computer is joined to a domain, members
of the Domain Administrators group might be able to modify the registry. As a security best practice, consider using
Run as when modifying the registry.

To open Registry Editor, click Start, click Run, and then type regedit.

Open the registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Parameters.

Right-click Type, select Modify and enter NTP.

Right-click NtpServer, select Modify and enter the Domain Name System (DNS) name or the IP address of an external
NTP server.

Open the registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpClient.

Right-click Enabled and enter 1.
Open the registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpServer.

Right-click Enabled and enter 1.

Public stratum 2 (do not use stratum 1) NTP time servers and NTP pool servers are available at and, respectively.  Be sure to read the rules of engagement at


Tere Stevens
Unified Communications PDI Team

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Last update:
‎08-10-2010 02:19 PM
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