By default, PoE NVRs are set to connect directly to IP cameras. In cases where the PoE ports are connected to network switches, the NVR must be put in Manual mode.
In addition, the PoE ports are set to Isolated mode, where each device can only communicate only with the NVR and not each other. This is a security feature to prevent rouge devices from accessing other devices on the network. This will prevent a connected PC from accessing IP cameras for setup changes.
If you are up linking non-camera devices, such as switches, media converters, PCs, etc., you must set the NVR to Manual mode.
From the setup menu of the NVR, navigate to System > System Management > Settings > Load Factory Default.
Select the Manual Setup Mode. If you wish to save some of the settings to speed up setup, check the Not Included options of User, Camera, and/or Network as needed.
Click the Initialization button and wait for the NVR to reboot.
On newer NVR models with the updated GUI you can find the setting under System > System Management > Settings tab
On newer NVRs the apply button for the PnP mode doesn't require initialisation.