When Reachability metric is enabled for accessible Windows device (SNMP service enabled), you are getting the below incorrect alert.
QOS_REACHABILITY_REACHABILITY = 0.0 from source XXX targeting Reachability has crossed the critical static threshold of < 100.0
QoS value of Reachability metrics for the device is showing as 0% while device is online and SNMP service is up running.
snmpcollector probe ANY VERSION
Windows device (SNMP service enabled) is being monitored.
SNMP V2 is selected for Windows device profile.
If you select SNMP V2 for profile, snmpcollector probe polls 20 oids in one snmp bulk request and SNMP service in Windows device is unable to respond to the request.
Change SNMP version from V2 to V1 in profile for Windows device.
MAX_BATCH (default 20) parameter controls how many oids snmpcollector polls in one bulk request.
This problem may also be solved with lower number of MAX_BATCH.
However lowering this parameter should only be done very carefully, because it may slow the entire polling performance down in snmpcollector probe.
See this for more details about MAX_BATCH.
Also reference this article for Reachability being 0 when the device is accessible with the snmpcollector probe version 4.03: