[mrtg] Re: Wan spikes

[Paul C. Williamson]

The easiest explaination is this:  MRTG does rates.  

MRTG retrieves a value.  No response.  MRTG, thinks, "Great, 
I'll just enter a zero."  Next time, gets the same thing, no response, 
zeo goes into the log.  Then the next time, it gets a response, and it 
is huge.  So the rate for that period of time is huge.  The problem is thec
 ounter was incrementing the whole time mrtg could not talk to the device,
but the device did not know that.  Then the next poll, it gets a huge+smallv
 alue, and puts that in as the rate between n and n-300 seconds.  It happens 
sometimes when you first start monitoring devices as well.  
It's a problem, but I don't know how I'd solve it with MRTG.  Sounds likeo
 nce you are able to poll the device, you need to reset the counters BEFOREm
 rtg can poll it again.  That will eliminate the possibility of the huge spike.
I know that isn't realistic all the time, but it may get someone thinking...

Paul

>>> WEYMIENS Bruno FTRD/DMI/SOP <bruno.weymiens at rd.francetelecom.com> 08/31/01 08:02AM >>>

hi everyone,

I confirm what Keery said : I've got spikes too when information is
retrieved again after a period of no value.

as i'm polling a SNMP MIB, I could check the MIB when it happens, but I'd
have to look at the graph continuously to see a spike and to look at the MIB
immediately...
:-(
hard to do...

I'll try to simulate a problem and see if it happens, but if someone as a
clue, it'd be appreciated.

regards

-----Message d'origine-----
De : Kerry Kincaid. [mailto:kincaid at meer.net] 
Envoye : vendredi 31 aout 2001 13:23
A : MRTG (E-mail)
Objet : [mrtg] Wan spikes


I've a Digi Portserver at a remote location that I poll for Ethernet traffic
via SNMP.  However, if for any reason I can not get the value (link down,
high traffic, device problem) for a period of time, as soon as the
information is retrieved, a spike is recorded in my RRD graphs.  

Example:  yesterday my graph was steady at about 2kbps, and most values for
outgoing hover around 2kbps, for about two hours the value was 0 for some
unknown reason, after that two hour period, there is a spike in the graph at
8Mbps.  This is highly unlikely as there are only three terminal on this
unit, and it connects the terminals to a device at our main branch via a 56k
(28cir) frame relay link.  

Is there an option or configuration change that I haven't found in the
manual that can help me resolve this issue.  I have read the manual, but I
think I'm just looking at the right solution from the wrong point of view or
something.  Any help appreciated.

Kerry


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