Discovery - Classification criteria is missing/empty for OOTB Classifiers

[Suggy]

We know that

For each classifier, there will be classification criteria. That criteria contains the condition that a target host has to satisfy in order to trigger a relevant classifier. 

but for many OOTB classifiers, the criteria is empty.

Then how it works?

[doug_schulze · Accepted solution]

Via the SNMP SysOID, it calls the classifier.