Cause: The user would have manually chosen to unmanage the interface/device.
Solution: Managing and unmanaging of devices can be done individually or in bulk. To unmanage/manage devices in bulk, go to Settings -> Configuration -> Quick Configuration Wizard -> Manage/Unmanage. Select the set of devices and perform the necessary action. You can also perform the same action for individual devices from their respective snapshot pages.
Cause: The discovered/listed interface may be a subinterface. A subinterface is a virtual interface created by dividing one physical interface into multiple logical interfaces. A subinterface in a router uses the parent physical interface for sending and receiving data.
Solution: As of now, OpManager does not manage those interfaces which are listed as sub-interfaces. These interfaces will only be shown as unmanaged.
Cause: The parent/dependent device may be down or associated with an active Device Downtime Schedule. If the dependent device is associated with a downtime schedule (or unmanaged manually), the child device and its interfaces will also be moved to unmanaged state for that particular period.
Solution: Remove the particular device from the Downtime Schedule to start monitoring the interface.