[mrtg] Re: clearing of counters on Cisco

[Jim Witherell]

It probably wouldn't be too tough to load the new version on a test box,
point it at one of your devices for a few hours to get a part of a graph,
then do a clear counters and see how it acts. If you see your production
box has spikes, and the test one doesn't, then you have the answer to your
question!

My understanding of how current versions of MRTG should treat it would be
to compare the calculated measurement it to the MaxBytes field in that
interface configuration in your MRTG config file. It is supposed to be a
"sanity check". My impression is that if the value is above that MaxBytes
threshold, it will think the value is false and throw it out. It would then
use the last polled value again in your graph.

Check me on this! I may be mistaken! I have done a few clear counters this
last couple days on a few WAN links of mine that were having trouble, and
the graphs don't seem to have any odd looking spikes to me.

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


                                                                                                                                     
                      "Lindahl, Carl"                                                                                                
                      <crl at rti.org>            To:       "'Scott P. Daffron'" <scott at cs.odu.edu>, mrtg at list.ee.ethz.ch               
                      Sent by:                 cc:                                                                                   
                      mrtg-bounce at list.        Subject:  [mrtg] Re: clearing of counters on Cisco                                    
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                      01/24/03 11:32 AM                                                                                              
                                                                                                                                     
                                                                                                                                     





What version (possibly versions) of code are you running on your various
Cisco devices?

Are you using SNMP v1 or v2 to poll the devices?  If you are using v1, and
the counters are exceeding the 32 bit max, if the IOS or CatOS supports it,
you can goto SNMP V2 to give you 64 bit counters (any one feel free to
correct me if I'm wrong about this) to give you a better view of the
interface.


Carl

-----Original Message-----
From: Scott P. Daffron [mailto:scott at cs.odu.edu]
Sent: Friday, January 24, 2003 11:26 AM
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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