[mrtg] help with counter issue

[Roth, Gabrielle]

OK, I have managed to completely confuse myself.

I am using mrtg to monitor a series of ATM PVCs at a 10-minute interval.  On
the major interface, I get these funny dips periodically.  (Image attached,
will be removed by the listbot.)

It seems to me from what I've read and seen on this list that this is
probably a counter rollover issue.  The faq
(http://faq.mrtg.org/FAQ004.html) says "32 bit will allow for a maximum
value of 4294967295, and when divided by 300 (seconds) this is about 14
megabytes per second or 114 megabits per second."  But, I'm getting less
than 14 Mb:  when I add up the numbers from the sub-ifs, they add up to just
under 4 Mb.  I'm guessing this is because the *max* is 14M, and mine is just
showing less than that.  ???

I set up a shell script to grab the ifOutOctets from this interface every
two minutes.  It rolls over about every 20 minutes, which is more than my
polling interval.  Unfortunately I have no other WAN interfaces that are
running this much traffic so I can't make a valid comparison that way.

Am I missing something totally obvious or do I need to investigate this
link?

-gr 

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