Sorry, I don't grasp what you are saying. Indeed the example is a HVision NVR /w (16) PoE ports. And yes, there must be 2 interfaces at play for each camera.With apologies - for the avoidance of any confusion, assuming the example is a Hikvision NVR with PoE ports, there are 2 ethernet interfaces in play internal to the NVR.
The interface on the 192.168.254.0 network is dedicated to the PoE ports connected cameras.
And yes, 192.168.254.0 network is dedicated to cameras.
That said, my belief is (was?) that 192.168.254.0/24 is non-routable. Perhaps I am mistaken, it would not be the first time
However, no packets from the .254 network get to the WAN connection and I have not written any firewall rules to block them. Would you know a specific inbound or return IP range that I can monitor? I have only monitored outbound from the .254 IP's and I suppose if the camera's were to try to call home on a random or intermittent schedule I could have missed that.
I do not have any 'outside' services running on the NVR except NTP and that points to my firewall/router which is my NTP server.
My firewall blocks all inbound traffic that is unsolicited.
It's interesting that I got the idea for non-routable IP's for the camera's from a post you made a number of years ago. If the network address I am using is incorrect then I must have misread your post. Whatever, AFAIK the way I have it set up keeps my cameras & NVR off the internet and inside my LAN. I can access my LAN via locally hosted VPN server and my access the NVR via my mobile devices. No P2P, No Cloud, No 3rd party except my own system.
And thank you for all the knowledge you post at this site. I should visit here more often.