[mrtg] Re: bandwidth utilisation

[Barry_Young at interliant.com]

Andy,

You could be running into a counter wrap problem, indeed I have a similar
issue on a highly utilised Gig interface.  In some previous discussions on
this mailing list I believe we arrived at the conclusion that unless your
device support SNMPv2 64-bit counters, the counter values will wrap to zero
after approx. 4.2Gb of data transfer (ie. 2^32).  This very roughly equates
to a 14.3Mb/sec over a 5 minute period (2^32 / 300 secs).

Therefore during the 5 minute polling interval, the counter wraps and give
distorted results because MRTG compares the current value with the previous
polled value.

I am led to believe that RRDtool works better with 32-bit counters but as
yet have been unable to implement this approach.

Alternatively, if your device supports SNMPv2 use the ifHC* mib values to
use 64-bit counters that will not wrap so often.

HTH
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