[mrtg] Re: Mrtg does not display high values of traffic correctly??

[Jason Frisvold]

I never did get this to work...  Do I need to put any special commands
on the router itself?  (Cisco router)

---------------------------
Jason H. Frisvold
Senior ATM Engineer
Engineering Dept.
Penteledata
CCNA Certified - CSCO10151622
friz at corp.ptd.net
---------------------------
"Imagination is more important than knowledge. Knowledge is limited.
Imagination encircles the world." -- Albert Einstein [1879-1955]


-----Original Message-----
From: tony bourke [mailto:tony at vegan.net] 
Sent: Thursday, May 30, 2002 2:27 PM
To: Richard Cotrina
Cc: mrtg at list.ee.ethz.ch
Subject: [mrtg] Re: Mrtg does not display high values of traffic
correctly??


Hi Richard, 

The answer, as people have already stated, is to use SNMPv2.  

Here is a blurb on the technical reasons for the errors with v1:

One limitation to keep in mind is that with SNMPv1 MRTG or any other
SNMP
program) cannot accurately measure bandwidth above about 114 Mbps
(Megabits per second) based on 5-minute intervals. The reason is that
the
default interface counter is a 32-bit number, and a 32-bit number will
rollover twice in a period of 5 minutes at more than 114 Mbps. (232 =
4,294,967,296 bytes, multiplied by 8 (bits in a byte), divided by 300
seconds in 5 minutes, is 114,532,641 bits per second, or roughly 114
Mbps.) MRTG or any other SNMP program cannot correctly account for a
double rollover. The graph will appear to peak at about 114 Mbps and
never
go beyond that, when in reality the interface could be running well
beyond
that rate.  Using SNMPv2's 64-bit counters will overcome this.



On Thu, 30 May 2002, Richard Cotrina wrote:

> 
> Hello :
> 
> I am using mrtg to monitor the traffic going and coming through a
STM-1 POS
> interfaz in my Cisco Router. It was working fine until the values of
> incoming traffic started to be above 100Mbps.
> 
> The matter is that suddenly and without giving any errors in the log
file,
> the values displayed (also the graph) for the incoming traffic fall
down to
> very small values (a few kbps) but, in the orther hand, this does not
happen
> with the outgoing traffic, that remains displayed in its correct
values (
> it's usually not higher than 50Mbps ). This condition returns to
normality
> without any reason, and also when the traffic is lower than 100Mbps.
> 
> The result of this, is that my mrtg graphs shows an apparently loss of
> traffic, but it is not caused by any traffic interruption, because the
> outgoing traffic is displayed continously.
> 
> I was using mrtg 2.9.17 when it started to happen, then I upgraded to
> 2.9.18pre11 and got the same results.
> 
> Does anyone have an idea on what is going on ?  As i mentioned before,
the
> logs did not give me any error messages.
> Do I need a special option in the mrtg config file to handle high
values of
> traffic correectly ?
> 
> Thanks in advance for any help,
> 
> Richard Cotrina
> 
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Tony Bourke				tony at vegan.net


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