[mrtg] Re: Options: unknaszero

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Tue Dec 18 23:59:51 MET 2001

bernie dolan wrote:

> MRTG-2.9.17
> I have an interesting situation with unknaszero.
> The interface being polled has 5 x E1 interfaces from a PABX which treats each E1 as clear channel so what I end up with is 17.2 Megs per second of traffic on a 32bit counter which rolls every 35 to 40 minutes.
> In a 5 minute interval the *.log file shows the in & out deltas only vary a maximum of 800 bytes due the consistency of the traffic from the PABX.
> My problem is:
> If I DON'T use unknaszero, the traffic is so constant that any outages are missed on the graph as they are already straight lines.
> If I DO use unknaszero then every 35->40 minutes the graph shows a sharp dip as turning on unknaszero seems to override the normalization of rolling counters

MRTG (better: rateup) doesn't handle roll overs.  It will handle them as
unknowns.  You could try to use RRDtool as your back end for MRTG.  This
also means using (for instance) 14all.cgi to produce the images.

With RRDtool you can choose how to interpret missing data.  I'm not sure
if the current meaning of "unknaszero" is correctly implemented if you
switch over.  Rolling counters however are implemented in the back end.

To make sure you do spot outages you have to check your xff settings.  Do
this with "rrdtool info" (to check them) and "rrdtool tune" (to alter them).
You want to spot outages so the correct xff setting to use is zero.

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
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