[INFO] How do I stop this spike?

[joes3029]

Hi all,

I'm still working my way through a new and first time install of Cacti - I can see it being extremely useful! At the moment though, I'm monitoring (besides other things) traffic on my DSL router. The problem I have is that every time the device resets it's connection it shows a spike of 112Mb, which rather skews the normal data expected on a 384Kb line. I'd like Cacti to ignore this spike, so the logical thing to do would be to set the highest allowed data received by the poller.

Presumably I'd do this by going into Data Sources for that graph, and specify the maximum values allowed there, but I'm confused as to exactly what data I should set. It's a Counter32 type, measured in octets, and so logically I'd set a maximum value of 384Kb = 393216 bytes= 393216 octets, but as far as I can make out the other values selected are much higher - should I be multiply this out by 300 seconds given that the poller only retrieves data every 5 minutes, or am I missing the counter resetting to zero on the interface reset, and Cacti converting this to a large positive number?

[Howie]

The router shouldn't reset the counter when the interface goes down. That's incorrect behaviour.

Although actually, the IF-MIB standard says "Discontinuities in the value of this counter can occur at re-initialization of the management system, and at other times as indicated by the value of ifCounterDiscontinuityTime."

ifCounterDiscontinuityTime is { ifXEntry 19 }. So it would be worth doing an snmpwalk of 1.3.6.1.2.1.31.1.1.1.19 on your router and see if it is updating that value, or if it even exists. If it isn't then it shouldn't really be resetting the interface counters, and I would say it's a bug with your router.

If it does have that timestamp, and does update it, then Cacti should take notice of that fact, since it's specified in IF-MIB.