[mrtg] Re: Graph spikes with RRD log format

[Greg Reaume]

I'm just monitoring standard routers: BytesIn, BytesOut.  I'm only
missing two or three samples while the router is unreachable.  When I am
able to reach it, the first sample is a huge spike in the order of
6-10Mbps.  This doesn't always happen, usually only when the link is
down in the middle of the day over more than one sampling interval.

Any ideas?

Greg Reaume

Network Analyst
Cowan Dalton Inc 


-----Original Message-----
From: Inaki Sanchez [mailto:isanchez at unav.es] 
Sent: July 4, 2002 3:52 AM
To: Greg Reaume
Subject: Re: [mrtg] Graph spikes with RRD log format


Hi Greg,

What kind of device are you monitoring? This usually happens when you
configure the target as COUNTER. If the value MRTG reads is lesser than
the previous one, MRTG assumes the counter limit (32 or 64 bits) has
been reached and the counter has restarted at that point. If the
variable you are monitoring doesn't have this behaviour, it happens what
you say. With RRDTOOL you have the option of defining a variable as
DERIVE, but I'm afraid MRTG doesn't. If you set the MaxBytes option,
MRTG should ignore values higher than that... but I'm not pretty sure of
that.

Regards,

--Inaki.

Greg Reaume wrote:
> 
> I apologize in advance if this has been asked and resolved, but I've
> seen quite a few references to this in the archives but no definite 
> resolution.
> 
> Why is it that, if a device goes down or misses a poll due to packet
> loss, in the next poll I almost always see a huge spike in the tens of

> Mbps?  I understand that with MRTGs native log format it is easy to 
> get rid of this spike.  Is this also so with an RRD log format?  If 
> so, how? These spikes really ruin my long-term graph resolution.
> 
> I'd appreciate any assistance you can provide.
> 
> Greg Reaume
> 
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