Ok so I've now had three of the 20 cameras in my batch go down with the same issue. I do not know what's causing it but they just stop talking to the network for reasons unknown. One was attached to an NVR and the other two were hooked up to a BI machine. The issue does not appear to be IP address related, unless the camera has decided to change it's own IP address to something random. In each case I've fixed the issue by factory resetting and then flashing with
@cor35vet 's excellent firmware mod kit.
Dahua Firmware Mod Kit + Modded Dahua Firmware
I didn't think of using the camera discovery tool, as has been helpfully suggested by
@beingaware ,to see if I could locate the camera that way first. Unfortunately I had already fixed the issue before I logged in, and hadn't really considered the possibility that the camera may have chosen a random IP. I might give it a crack if any more go south though I suspect it will not work in my case due to the lack of any inter VLAN routing to whatever random IP the camera selects, if that is what is going on.
A bit of a tip that saved me a lot of work. In my case I created a new VLAN on the 192.168.1.1/24 range and allocated two of my POE ports to that so I could both power and talk to the camera after I reset it. All my camera's are in a very different IP range normally. If your switch doesn't have the ability to do that, and you are working from an IP range other than the 192.168.1.1/24 I would recommend having a cheap POE injector lying around to facilitate powering a direct link with the camera until you have been able to flash the firmware and get its IP address settings fixed. It is a lot less work than taking down the camera entirely to power it from 12V.
