[mrtg] MRTG Math problem

Steve Shipway s.shipway at auckland.ac.nz
Tue Jan 25 21:47:33 CET 2011

 Since the problem only occurs on the calculated Target, and the combined total is close to 150Mbps (the 5min rollover point for 32bit counters) I wonder if it is caused by either (a) the 32bit counters being used even though SNMPv2 is being specified or (b) a bug in the MRTG wraparound calculation?

You might like to upgrade to the latest MRTG (2.17) just to be sure that there are no fixed bugs, although the CHANGES file doesnt mention anything specific to this issue.

Try using Option[]:derive on the target that has the problem, as I think this disables wraparound detection (you'd get a big negative value when it DOES wrap around, but this would be dropped by the RRD min/max range)

One workaround (if you are using MRTG/RRD/Routers2) is to define a totalled userdefined summary graph over the two component targets, rather than create a separate target that retrieves the two values and adds them.


Steve Shipway
University of Auckland ITS
UNIX Systems Design Lead
s.shipway at auckland.ac.nz<mailto:s.shipway at auckland.ac.nz>
Ph: +64 9 373 7599 ext 86487

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