Introduction:
This document covers troubleshooting approach when working on NTP issues with CUCM and other UC APPS.
Pre-Requisite:
Knowledge of NTP and CUCM
Recomendation:
1. NTP is a Client\Server protocol which communicates over User Datagram Protocol (UDP) on port 123. Cisco highly recommends the use of a Stratum 1, Stratum 2, or Stratum 3 NTP server as the CUCM Publisher's external NTP reference. Any NTP source for the CUCM publisher MUST NOT be higher than stratum 4.
You can check the stratum by running the command "Utils NTP status"
Refer to the output of the NTP status from CUCM server:
admin:utils ntp status
ntpd (pid 26049) is running...
remote refid st t when poll reach delay offset jitter
==============================================================================
*172.18.108.15 .GPS. 1 u 538 1024 377 262.732 0.044 0.006
synchronised to NTP server (172.18.108.15) at stratum 2
time correct to within 22 ms
polling server every 1024 s
What is NTP stratum?
--> Stratum basically define the distance from the reference clock. A reference clock is a stratum-0 device that is assumed to be accurate and has lttle or no delay associated with it.
--> The reference clock typically synchronizes to the correct time (UTC) using GPS transmissions, CDMA technology or other time signals such as Irig-B, WWV, DCF77, etc.
--> Stratum-0 servers cannot be used on the network, instead, they are directly connected to computers which then operate as stratum-1 servers.
--> A server that is directly connected to a stratum-0 device is called a stratum-1 server.
--> A stratum-2 server is connected to the stratum-1 server OVER A NETWORK PATH. Thus, a stratum-2 server gets its time via NTP packet requests from a stratum-1 server. A stratum-3 server gets its time via NTP packet requests from a stratum-2 server, and so on.
Refer to the output below from the CUC server which uses CUCM as an NTP server:
admin:utils ntp status
ntpd (pid 30358) is running...
remote refid st t when poll reach delay offset jitter
==============================================================================
*10.106.117.132 172.18.108.15 2 u 265 1024 377 0.836 0.365 0.071
synchronised to NTP server (10.106.117.132) at stratum 3
time correct to within 58 ms
polling server every 1024 s
Current time in UTC is : Sun Apr 23 04:25:50 UTC 2017
Current time in Asia/Kolkata is : Sun Apr 23 09:55:50 IST 2017
2. Its important to note that the external NTP servers defined for the CUCM Publisher node shoud be NTP v4 to avoid any issues and also note, NTP version 4 is backward compatible with version 3; however, many issues were observed with attemps to use different NTP versions.
You can verify the NTP version by running a capture on the CUCM on port 123 using the command "utils network capture port 123". When you run a capture, you should see client/server messages showing the version.
admin:utils network capture port 123
Executing command with options:
size=128 count=1000 interface=eth0
src= dest= port=123
ip=
20:53:40.580043 IP cucdm1052.ciscohcs.com.ntp > cucmp.ciscohcs.com.ntp: NTPv4, Client, length 48
20:53:40.580929 IP cucmp.ciscohcs.com.ntp > cucdm1052.ciscohcs.com.ntp: NTPv4, Server, length 48
20:54:01.475784 IP cuc.ciscohcs.com.57306 > cucmp.ciscohcs.com.ntp: NTPv4, Client, length 48
20:54:01.476561 IP cucmp.ciscohcs.com.ntp > cuc.ciscohcs.com.57306: NTPv4, Server, length 48
20:54:01.477423 IP cuc.ciscohcs.com.57306 > cucmp.ciscohcs.com.ntp: NTPv4, Client, length 48
20:54:01.478786 IP cucmp.ciscohcs.com.ntp > cuc.ciscohcs.com.57306: NTPv4, Server, length 48
3. Make sure you use an IOS based NTP server as windows based NTP servers are not supported.
Logs Required:
While troubleshooting NTP issues, you need to collect the following:
1. Utils ntp status
2. Utils diagnose test
Packet captures from the server on port 123.
Regards,
Aseem Anand
