Currently I have a Dahua 4108 NVR connected to Dahua cameras. On the NVR and cameras, NTP is both unticked. When looking at the stored video, it time appears to correlate with the NVR as the cameras are slightly out of sync. I have noticed the NVR time slowly goes out of sync with the real time, so I manually use the "sync PC" command.
Instead of having to do this manual sync, I was wondering about using the NTP option. Currently my router blocks all outgoing ports from the NVR with the exception of port 8888 to enable notifications to be sent when the tripwire is triggered. I ticked the NTP option and also "manual update" not expecting it to work as port 123 outgoing is blocked. However it seems to sync with NTP. Now several days later, the time still is syncing perfectly so I assume the NTP is working.
This leads me to the question, why NTP is working even though outgoing port 123 is blocked.
Instead of having to do this manual sync, I was wondering about using the NTP option. Currently my router blocks all outgoing ports from the NVR with the exception of port 8888 to enable notifications to be sent when the tripwire is triggered. I ticked the NTP option and also "manual update" not expecting it to work as port 123 outgoing is blocked. However it seems to sync with NTP. Now several days later, the time still is syncing perfectly so I assume the NTP is working.
This leads me to the question, why NTP is working even though outgoing port 123 is blocked.