NTP on Cisco IOS and CUCM

NTP Overview

The Network Time Protocol (NTP) synchronizes the time of day among a set of distributed time servers and clients so that you can correlate events when you receive system logs and other time-specific events from multiple network devices. NTP uses the User Datagram Protocol (UDP) as its transport protocol. All NTP communications use Coordinated Universal Time (UTC).

An NTP server usually receives its time from an authoritative time source, such as a radio clock or an atomic clock attached to a time server, and then distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two machines to within a millisecond of each other.

NTP uses a stratum to describe the distance between a network device and an authoritative time source:

•A stratum 1 time server is directly attached to an authoritative time source (such as a radio or atomic clock or a GPS time source).

•A stratum 2 NTP server receives its time through NTP from a stratum 1 time server.

Before synchronizing, NTP compares the time reported by several network devices and does not synchronize with one that is significantly different, even if it is a stratum 1.

NTP Configuration in IOS

In the Lab you are asked to sync the Router clocks (HQ, Branch1 and 2) and CUCM with NTP server which is pre-configured in lab. You will be given the NTP server IP address.

To sync the Router with NTP server and configure the timezone, you need to use below command:

Router(config)# ntp server <ip address of ntp server> prefer
Router(config)# clock timezone PST -8           ! It means you PST timezone is UTC -8
Router(config)# clock summertime PST recurring
Router# show ntp status

If external NTP server is not provided and you are asked to create a Router act as a NTP server then use below command:

Router(config) # ntp master
Router(config)# ntp source loopback0   ! NTP packet will be sourced from Loopback interface

NTP is a slow protocol it will take some time to synchronize with the ntp server. So give it some time to synchronize.

NTP Configuration in CUCM

On CUCM, we define the NTP server only on the Publisher Node. Subscriber node automatically sync with Pub node.

Step 1  From the Cisco Unified Communications Operating System Administration window, navigate to Settings > NTP Servers.

The NTP Server Settings window displays.

Step 2  You can add, delete, or modify an NTP server:

  • To delete an NTP server, check the check box in front of the appropriate server and click Delete.
  • To add an NTP server, click Add, enter the hostname or IP address, and then click Save.
  • To modify an NTP server, click the IP address, modify the hostname or IP address, and then click Save.

Step 3  To refresh the NTP Server Settings window and display the correct status, choose Settings > NTP.

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

To check the NTP status on CUCM, you need to ssh to CUCM CLI and run below command:

utils ntp status

Hope you found this post useful. If you have any query, please leave a comment.