CUCM 7 As NTP Server

Unanswered Question
Jul 26th, 2010

We have CUCM version 7 is it possible to run it as NTP server so routers,Switches and access Points Sync. time with it and If possible how could I do configure this?

Thanks and best regards

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htluo Mon, 07/26/2010 - 08:06

Usually, CUCM will sync the time from the router, not the reverse.

Once the time was synced, CUCM publisher will also be acting as a NTP server.  So CUCM subscribers and sync the time from publisher.


Jaime Valencia Mon, 07/26/2010 - 08:20

Indeed, you should follow the best practices.

Cisco IP Telephony Clock Synchronization: Best  Practices

• For Cisco Unified CallManager Versions 5.0 and  later:

– Manual configuration of the ntpd.conf file is not  allowed.

– Cisco Unified CallManager prompts the  administrator to specify the external NTP server at publisher  installation and automatically populates the ntpd.conf file on the  publisher server.

– The ntpd.conf files of all other cluster servers  are automatically configured to point to the publisher as the NTP  source.

•  Configure the publisher to point to a traceable stratum 1 clock source.

•  Configure network latency between the publisher and the dedicated clock  source so that it is within 40 milliseconds round-trip time (RTT).

• For  additional information about NTP time synchronization for Cisco Unified  CallManager, please refer to the Solution Reference Network Design  (SRND) guide for your specific version at

From  SRND:

Unified CM NTP Time Synchronization
Time synchronization is especially critical on Unified CM servers. In  addition to ensuring that CDR
records are accurate and that log files are synchronized, having an  accurate time source is necessary for
any future IPSec features to be enabled within the cluster and for  communications with any external
Unified CM 5.0 and later releases automatically synchronize the NTP time  of all subscribers in the
cluster to the publisher. During installation, each subscriber is  automatically configured to point to an
NTP server running on the publisher. The publisher considers itself to  be a master server and provides
time for the cluster based on its internal hardware clock unless it is  configured to synchronize from an
external server. Cisco highly recommends configuring the publisher to  point to a Stratum-1, Stratum-2,
or Stratum-3 NTP server to ensure that the cluster time is synchronized  with an external time source.



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Leo Laohoo Mon, 07/26/2010 - 19:14

I wouldn't configure Cisco appliance as an authoritative NTP server.

If you have Windows servers, you can configure them to be an authoritative NTP server.

How to configure an authoritative time server in Windows XP

How to configure an authoritative time server in Windows Server

How to configure an authoritative time server in Windows 2000

Otherwise, use a dedicated NTP server that synchronizes itself using GPS.  The reason why I don't recommend a Cisco appliance as an authoritative NTP/SNTP server is because the clock chip is similar to a PC.  It doesn't have a dedicated method of verifying.  You can get a cheap NTP server that uses GPS (best method so far).  Another option is to open a port in the firewall to allow the device(s) to talk to world-wide NTP pool.


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