This article applies to DVRs or NVRs that are hardwired to your router, and affects mobile or computer streaming, push notifications, and other features requiring internet connectivity.
The DVR or NVR going offline is a common occurrence when changes were made to the router, its settings, an outage, or changes in IP by your Internet Service Provider (ISP). In order to get it back online, you must have physical access to the DVR or NVR to check the following:
1. If there was a Power or Internet Outage
Normally, turning off the recorder and then turning it back on again will get the DVR or NVR to re-establish communication with your router. However, this will only work if its Network setup is set to DHCP by default. This ensures that the router is able to detect the DVR/NVR via ethernet and update its IP address.
If rebooting did not work, please try additional steps from this article: Remote Access - Basic Router/Network Troubleshooting.
If the live view is blank, then the outage may have affected the power supply. Check this article to troubleshoot: Troubleshoot a Boot Failure or Rebooting issue of a Recorder (DVR/NVR/NVW).
2. If you changed or replaced the router (changed ISP)
See types of routers that may or may not work with the DVR or NVR in this article: Network Setup: What do I need for my DVR/NVR to go online?
If the router is compatible, then the connection between the recorder and the router just needs to be refreshed. See this article for the first few steps to re-establish the network connection: Remote Access - Basic Router/Network Troubleshooting.
3. If you added another router or extender
Ensure that the network connection setup has not changed. If the DVR or NVR is still connected to the same router, but that router was connected to a cable modem instead of a wall, then the setup is no longer a direct connection but a bridged connection.
See why the DVR or NVR may not work with a bridged router or particular extender in this article: Network Setup: What do I need for my DVR/NVR to go online?