Showing results for 
Search instead for 
Did you mean: 
Hall of Fame Community Legend

Cisco CUCM NTP documentation/requirements

Hello all,

Just wondering about the "actual" NTP clock Stratum version requirements when

installing Cisco CUCM. As the three sources below show varying results;

So first we have the install guides;


Cisco   recommends that you use an external NTP server to ensure accurate   system time on the first node. Ensure the external NTP server is stratum   9 or higher (meaning stratums 1-9). Subsequent nodes in the cluster   will get their time from the first node.When you are installing   Cisco Unity Connection on a virtual machine, you must specify an   external NTP server.

Then the SRND;

Unified CM automatically synchronizes 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.

And finally the NTP  White Paper;

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).

Thanks for any light you can shed on this.



"Spend your life waiting,
for a moment that just don't come,
Well, don't waste your time waiting" 



Cisco CUCM NTP documentation/requirements


Did you ever get a response from Cisco to this post?  Or get your question answered through a different medium?


Hall of Fame Community Legend

Cisco CUCM NTP documentation/requirements

Hi Marc,

Sorry for the late response here

Nothing but the sound of crickets...................



"May your heart always be joyful
And may your song always be sung
May you stay forever young " 

- Dylan


Hi,we also experienced this


we also experienced this discrepancy on this deployment, anyway we just followed the SRND - besides having a more reliable clocking will lead to stability and help us a lot on our troubleshooting.

Actually, my question in reference to the OS administration guide on NTP settings (Versions 5.x up to 10.X has this note)


"NOTE: After deleting, modifying, or adding NTP server, you must restart all the other nodes in the cluster for the changes to take affect."


- is a cluster reboot really required?

- what will be the impact if this is not followed?


thanks for the advice!



Rising star

Hi,Answering this old post,


Answering this old post, Stratum 3 is required to be able to syncronize with a NTP Server. At the end, the Publisher will become a Stratum 4 for subscribers.

Startum 5 or higher will be rejected: "NTP servers with stratum 5 or worse clocks are deemed unreliable."



Please remember to rate useful posts clicking on the stars below.
LinkedIn Profile:

Leo, Do you have reference


Do you have reference for this. 

Still murky waters:

In 9.1 release Stratum 5 no longer enforced.

External NTP Server Requirements

The procedure "Set up first node" has been updated to remove the requirement that the external NTP server be Stratum 5 or higher. When you configure the first node, Cisco 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.



Rising star

Hi Jurek,No, but you can use

Hi Jurek,

No, but you can use my own personal experiences as a reference :). I have test this on a production system.

At least for CUCM9.1, NTP Stratum 5 or higher will not work, maybe will work just for the initial installation process.



Please remember to rate useful posts clicking on the stars below.
LinkedIn Profile:
Cisco Employee

Hi all, I have a customer

Hi all,


I have a customer running cucm with Stratum 5. They are getting NTP alert every minute.  Does this mean Stratum isn't recommended for this cucm version?


admin:utils diagnose module ntp_stratum


Log file: platform/log/diag2.log


Starting diagnostic test(s)


test - ntp_stratum         : Failed

The reference NTP server is a stratum 5 clock.

NTP servers with stratum 5 or worse clocks are deemed unreliable.

Please consider using an NTP server with better stratum level.


Please use OS Admin GUI to add/delete NTP servers.


Cisco Employee

(For people who come to this

(For people who come to this thread from Google search)

Doc from TAC has been published recently to address NTP troubleshooting.

Best Regards,

Sudheer Shenoy

CreatePlease to create content
Content for Community-Ad
August's Community Spotlight Awards