The counter rollover occurs when the snmp counter has reached its maximum. By
default SNMP uses 32bit counters.
In a 32bit counter the maximum number wich can be stored is 2^32-1. After this
the counter resets to 0 and starts counting up to ist maximum again. This reset
to 0 is called the counter rollover.
MRTG has an build in mechanism that deals with counter rollovers: When the
current value of the counter is lower then the previous value there must have
been a counter rollover. Because there is no way to detect if there has been 1
or more counter rollover MRTG assumes there has been 1 rollover, and in the
calculations the counter maximum is added to the current value.
Counter rollovers occur frequently: When polling your target once per 5 minutes
the rate per second is:
(current poll value - previous poll value) / 300 seconds.
When doing some calculalations you will find the counter rollover occurs every
5 minutes with a bandwith usage of about 114Mbit/s.
When graphing multiple target from one targetline there is a chance for a
counter rollover in each individual target. This is where MRTG fails to graph
the rate correctly: It can not know how many counter rollovers have occured in
the last polling interval.
What makes things even worse: When one counter rollover occured on one of the
targets, and the other targets together processed enough data to compensate
this rollover it is not even possible to detect the only one rollover!
When using 64bit counters the limits are way higher, but the basic problem will
be the same.
When storing the data in rrd format, the data for each individual target is
stored after the counter rollover calculation. Now you can retrieve and
summarize the data in a more reliable way.
HTH,
Jan.
-----Original Message-----
From: NAP [mailto:[EMAIL PROTECTED]
Sent: Friday, September 07, 2007 3:13 PM
To: Koelstra, J. (Jan)
Subject: RE: [mrtg] Error in sum interfaces
My sum is with 5 interfaces
this my Target. My problem will be here?
Only show 3 interfaces
Target[myrouter]: /x.x.x.x:[EMAIL PROTECTED]:::::2:+/y.y.y.y:[EMAIL
PROTECTED]:::::2:+/z.z.z.z:[EMAIL PROTECTED]:::::2:
I'm beginner in mrtg and don't understand what do you say with counters
rollovers and rrd for backend it
Tell me about my Target, and what I could do?
So Thanks.
_____
De: Koelstra, J. (Jan) [mailto:[EMAIL PROTECTED]
Enviado el: viernes, 07 de septiembre de 2007 4:33
Para: NAP; [email protected]
Asunto: RE: [mrtg] Error in sum interfaces
How do you create the graph with the sum?
When using a cfg file with Target: [EMAIL PROTECTED] + [EMAIL
PROTECTED] + ... you will almost certain run into problems with counter
rollovers.
Without rrd for backend it isn't possible to create summarized graphs
of (bandwith-)rates that are 100% accurate.
HTH,
Jan.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of
NAP
Sent: Wednesday, September 05, 2007 7:52 PM
To: [email protected]
Subject: [mrtg] Error in sum interfaces
We have problem with interface sums. The values in the
independent graphics don't correspond to the total value that we graphic.
The file .cfg of independent interfaces and the sum graphic is
the same.
What will be the problem?
We need help
Thanks,
_________________________________________________________
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de geadresseerde bent of dit bericht abusievelijk aan u is toegezonden, wordt u
verzocht dat aan de afzender te melden en het bericht te verwijderen. De staat
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houdt met risico's verbonden aan het elektronisch verzenden van berichten.
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This message may contain information that is not intended for you. If you are
not the addressee or if this message was sent to you by mistake, you are
requested to inform the sender and delete the message. The state accepts no
liability for damage of any kind resulting from the risks inherent in the
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