[mrtg] Re: clearing of counters on Cisco - again

[Jim Witherell]

That makes more sense. Good tip, too, as I was thinking of moving to
RRDtool at some point (when I get more sophisticated). What is the reason
for your NMS doing the counter reset? Is it a scheduled thing, or is it
triggered by other conditions? If it is scheduled, maybe the thing to do is
just expect to see the spike at a certain point on the graph, or move the
reset event to, maybe at midnight so it is easy to spot as a non-event.

Jim Witherell
Network Specialist                        --Live Intentionally--
IBM @ AK Steel Corp
513.425.3483


                                                                                                                                     
                      "Scott P.                                                                                                      
                      Daffron"                 To:       mrtg at list.ee.ethz.ch                                                        
                      <scott at cs.odu.edu        cc:                                                                                   
                      >                        Subject:  [mrtg] clearing of counters on Cisco - again                                
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                      01/27/03 12:25 PM                                                                                              
                                                                                                                                     
                                                                                                                                     





After spending a couple of days on this now, I have determined that MRTG,
when used alone, does not show this behavior.  The problem is only with
MRTG + RRDTOOL + 14all.cgi.  I've even downloaded and set up the newest
versions of each only to get the same result.  Does anyone how I can have
RRDTOOL and 14all.cgi follow the same logic as MRTG when creating graphs
(eliminating this spike)?

More info on my setup:
- Switches are Cisco Cat 4006 and 5XXX
- Our NMS is resetting all port counters by doing an snmpset on
  private.1.9.5.1.1.13.0.  Most people do not believe me, but this DOES
  reset the ifOctets value to 0, by design.


---------- Forwarded message ----------
Date: Fri, 24 Jan 2003 11:25:47 -0500 (EST)
From: Scott P. Daffron <scott at cs.odu.edu>
To: mrtg at list.ee.ethz.ch
Subject: [mrtg] clearing of counters on Cisco


Oh most wise MRTG gurus,

We have noticed that our version of MRTG (a couple years old) shows a huge
spike on our Cisco interface graphs whenever a "clear counters" is done on
the device.  This is becoming a big problem for us, as we have just
implemented a new NMS which clears all counters once per day.

I know this is an issue of the OID counter wrapping, leading MRTG to think
that a massive bandwidth spike has indeed occurred, but is there a way to
configure MRTG not to draw this conclusion (and alleviate all of the
massive spikes in our graphs)?  Does a newer version of MRTG handle this
differently?  I have looked high and low, but can't seem to find an answer
on this.  Thanks in advance...


Scott Daffron
Network Engineer
Sentara Health Care



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