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What does the network interface speed and volume sensor truly measure?

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We have a Cisco router that we are monitoring an interface on. The sensor polls every 60 seconds and checks the In/Out speed and the In/Out data volume. What exactly do those figures mean? In other words, is the speed a measurement of the current speed at the time of the poll, or is it an average speed since the last check or is it using Cisco's built in 5 minute average value? Also, if it is measuring the speed at the exact moment of the poll, how would we know if there was a major spike in traffic between the interval of time that we checked? I suppose we would just decrease the interval from 60 seconds to something more like 20 seconds. Is that correct?

Thanks, Zack

bandwidth cisco current-speed interface speed

Created on Mar 26, 2010 9:02:57 PM



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Accepted Answer

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Dear Zack,

basically we use delta-counters for bandwidth monitoring (for both Netflow and SNMP). This will give you, just as you said, an average of the traffic in the last 60s, if 60s is the scanning interval. Thus, small minimums and maximums in the 60s, will be averaged.
If you need more details, you could of course switch to a lower scanning interval, however please consider that this means a significantly higher load. For PRTG but also for the target devices, we have seen cases where switches reliably responded only if the scanning interval was at least 30s (the counters in the device simply weren't refreshed fast enough).

Best Regards.

Created on Mar 30, 2010 1:44:37 PM by Torsten Lindner [Paessler Support]



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Great info here. This was my exact question. To expand a bit, if you're not getting true peak readings and you're trying to determine how much bandwidth you need (in my particular case for a subnet), what do you use? Is there some general best practice - like take the highest 1 minute average and double it or some other arbitrary factor?

Thanks, Allen M.

Created on Nov 12, 2010 7:22:49 PM




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