Smarts 10.1.X
The environment contains Restricted MIBs. The absence of an expected entity (such as the Fan and Power Supply in the above problem symptom) can be caused by the MIB being restricted at the device level, which can impact Smarts IP discovery.
Restricted MIBs
Restricted MIBs are used in some locations for security purposes so that only a limited MIB is available to be polled from a device. For the Cisco 3750 Router device mentioned in the above problem symptom (SysOID .1.3.6.1.4.1.9.1.544), the Fan is created from FanState OID .1.3.6.1.4.1.9.9.13.1.4.1.3, while the power supply is created from PowerSupply OID .1.3.6.1.4.1.9.9.13.1.5.1.3.
If you looked in the SNMP walk file of the device where the MIB has been restricted for these entities as in the following example, you would see that neither of these OIDs are present:
ASL File: ic-cisco-router-health.asl
ciscoEnvMonFanDescrOID { ciscoMIBOID ".9.13.1.4.1.2" }
ciscoEnvMonFanStateOID { ciscoMIBOID ".9.13.1.4.1.3" }
ciscoEnvMonSupplyDescrOID { ciscoMIBOID ".9.13.1.5.1.2" }
ciscoEnvMonSupplyStateOID { ciscoMIBOID ".9.13.1.5.1.3" }