I have a cisco 7911 phone (IP 10.3.1.27) which uses an ntp server on the network.
The server is a cisco router (IP 10.3.1.252) that is used by all devices on the network for ntp.
The phone is picking up the IP of the ntp server form its xml config file, and can communicate with it.
The ntp server is responding back ,but the phone is not synching with the ntp server.
It still has its manufacture date (April 15, 2008)as reference and uses it after every reboot.
The phone is running sip firmaware SIP11.8-3-5S.loads which loads the following files::
jar11sip.8-3-4-16.sbn, cnu11.8-3-4-16.sbn, apps11.8-3-4-16.sbn, dsp11.8-3-4-16.sbn, cvm11sip.8-3-4-16.sbn
Could it be an issue with the ntp server ,or the phone firmware.
I have attached a wireshark capture of the interaction between the phone and the ntp server.
Not sure if you can be able to access Capture.pcap because pcap is not a among the formats you can attach.
If you can then all good but if not,rename Capture.txt to Capture.pcap .