A device may be categorized as Unknown due to the following reasons.

1. Discovery credentials may be incorrect.

Cause: Configuring your device with the wrong credentials will affect the discovery process. The configured credential may be incorrect or not supported by the discovered device. These devices will be categorized as unknown, because the provided credentials will not allow OpManager to access those devices and fetch the necessary details. 

Solution: Rediscovering the device by configuring the correct credential will solve the issue. To avoid such errors, use the Test Credential option under Discovery to check and confirm if the selected credential is supported by the device. 

2. Port may have been blocked in your environment.

Cause: ICMP port block: Few environments might have blocked ICMP port (ping) for security reasons. Since OpManager uses the ping function to check the availability, devices in these environments will not be reachable by the OpManager server during discovery. 

Solution: Make sure ICMP is enabled in your destination device and it is reachable from the OpManager server. Also ensure the default ports are made available.

3. Device type/Sysoid may not be listed in OpManager's default templates

Cause:  OpManager comes pre-loaded with 9500+ device templates and 292 interfaces template as default. In addition, it also carries 52000+ Vendor templates to categorize the monitored device precisely. If the monitored device is from a different manufacturer or type other than the present ones, that particular device may be categorized as Unknown. 

Solution: This issue can be rectified by adding custom device template to OpManager. 

4. The discovered device may not be reachable.

Some devices may be not reachable from the OpManager server at the time of discovery. In such cases, OpManager will categorize them under 'Device not monitored' state. 

Note: The points listed are also applicable for devices added to other modules such as NFA, NCM, FWA, and OpUtils