Currently we are developing a small tool to monitor the interface utilization on Fortigate 50E and 60E. In order to achieve this, we are polling the IF table (via SNMP). Our calculation goes as follows:
Input Utilization = (Delta_ifInOctets * 8 * 100)/(Number of seconds in delta * ifSpeed)
Output Utilization = (Delta_ifInOctets * 8 * 100)/(Number of seconds in delta * ifSpeed)
The formula above comes from Cisco recommendations (that I believe it is a valid approach for any network device). Until now we are able to measure the utilization without problems, however we were requested to increase the granularity of these measures, which means that we need to poll faster these OIDs. I went through the documentation available in Fortigate Help, but I could not find what is the highest frequency that these OIDs can be polled. Checking other replies in the forum, I saw 60 seconds as the fastest polling speed (since the device updates the SNMP statistics every 60 seconds). Is it possible to poll these OIDs faster? and if so, what the fastest polling that I could apply without harm the performance of the device?
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