Snmpcollector probe reporting 0% availability for a device that is available.

Document ID : KB000013291
Last Modified Date : 14/02/2018
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Question:

I have a device that is known to be active and available and it is reporting with 0% availability in USM. Why would this be?

Answer:

Availability is represented on a device by timeticks from the last time the device was rebooted. Timeticks are represented in centiseconds. We validate the delta (a calculation based on 2 sequential polls) against the duration between the two polls. There is a small time shift that is allowed in the calculation. The calculation looks like this:

300 seconds (representing a 5 minute poll interval) - 1 second per minute of duration - 2 seconds as the general allowed shift = 293 seconds

In the above this would represent 29300 centiseconds (timeticks). This is the minimum allowable value for the delta of a 5 minute poll cycle to report 100% availability. Anything lower than this would report the device at 0% availability.

The easiest way to determine if the device is reporting inaccurate timeticks would be through the use of Wireshark on the snmpcollector probe machine, filtering on IP of the device. After capturing a few poll cycles the data for 1.3.6.1.2.1.1.3 can be calculated, subtracting a previous data point from a later. 

example:

144078300 (data point from 1:05pm) - 144050200  (data point from 1:00pm) =  28100

Since the above is less than the required minimum of 29300 the availability will be calculated as 0%. In cases like this it is best to reach out to the device vendor to determine why the device is not keeping track of sysuptime correctly.