This thread is ridiculous – 67 posts for a simple problem, not yet resolved.
I suspect that we were misled by an incorrect observation and suggest that we start over.
On the PBX, capture traffic on the 172.16.26.x interface and have the phone request the time. There are three plausible results:
- No NTP request comes in.
- Requests come in but no replies are sent.
- Requests come in and valid responses are sent.
If it’s (2), it’s a problem on the PBX. Briefly disable the firewall to see whether that’s the culprit. Then, fix the firewall or the NTP server, as appropriate.
If it’s (1), use port mirroring on the switch to capture traffic at the phone. If the phone is sending requests properly (correct IP address, port, VLAN tag), you’ve got a simple network issue. If it’s sending improperly or not at all, it’s a provisioning or DHCP issue (for example, phone is getting NTP address from DHCP server that is handing out the address of the old PBX).
If it’s (3), use port mirroring on the switch to capture traffic at the phone. If the phone is receiving NTP responses properly, a provisioning or firmware issue. If the responses are missing or corrupted, a simple network issue.