How long does and interface or node show unknown before changing state to down in NPM? Also, where do you change those settings?
That should be based on your polling cycle. The next time the device is polled it should change state if the state is different. You can hurry this along by forcing a poll (Poll Now on the device summary).
Also, you can set each devices polling individually on the device's properties page, or you can change polling for all devices in multiple areas. The global settings are in the admin console, under Settings>Polling Settings (right side of the admin console by default).
