Why is NTP Unsynchronized?

Refer to the exhibit. A network engineer is troubleshooting a NTP synchronized issue in CUCM. Why is NTP Unsynchronized?


A. The NTP server used is a Windows based NTP server
B. The IOS Command NTP server 172.25.140.151 version 3 is advertising NTPv3
C. The NTP server stratum is higher than four
D. A firewall is blocking NTP port 123

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3 thoughts on “Why is NTP Unsynchronized?

  1. B
    16:03:03.689725 IP cucmlab.cisco.local.34063 > linux.local.ntp: NTPv4,Client, length 48
    16:03:03.690174 IP linux.local.ntp > cucmlab.cisco.local.34063: NTPv3,Server, length 48

    CUCM sends an NTPv4 packet and in response you receive an NTPv3 packet. Although NTPv4 is backward-compatible to NTPv3, CUCM implementation of NTP varies, which results in unsynchronized NTP:
    admin:utils ntp status

    ntpd (pid 22458) is running…

    remote refid st t when poll reach delay offset jitter
    =================================================================
    172.28.5.9 .INIT. 2 u 45 64 377 0.374 492.965 18.189

    In order to fix the issue, Cisco recommends you use a Linux-based external NTP server or Cisco IOS® or IOS XE-based NTP server and ensure that NTPv4 is configured.

    A is a possiblity but the SRND specifically mention that Windows NTP server is not supported and it would be a Stratum 2 as I understand it.

    1. Windows server = The NTP provider follows the standards specified by NTP version 3 for a client and server

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