I have recently upgraded a graph from 32 bit to 64 bit counters, and am now
getting unexpected (and I think incorrect) spikes in the graphs. All ideas
welcome.
I have a network with multiple VLANs. A layer3 wirespeed switch (an old
3Com Coebuilder 3500) is attached with a single Gigabit interface.
Traffic from the backbone concentrator runs out to the switch, changes VLAN
and is forwarded to the destination, Therefore Inbound equals outbound.
I was measuring this using standard 32 bit counters. This showed traffic at
50 Mb or so.

I wondered whether this was correct, or whether the counter was wrapping.
So I upgraded to 64 bit counters (I had to use OIDs, as :::::2 does not
work)
The new graph shows the same basic data level, but also has 100Mb spikes,
with the traffic shown in only one direction at a time. This seems wrong,
teh network design should not have a massive imbalence.

I am using MRTG 2.9.22 with RRD, running on w2k workstation (SP3), at 5 min
intervals, and viewed through Routers2.cgi.
The config contains:
Unscaled[_]: d
Options[_]: bits, growright, nopercent
routers.cgi*Options[_]: nomax interface
MaxBytes[_]: 250000
AbsMax[_]: 125000000
Target[wdh3500_1]: ifHCInOctets.1&ifHCOutOctets.1:public@3500-1

I have fired up STG (from http://leonidvm.chat.ru) on my desktop, set to 5
second polling. One STG session is monitoring ifInOctets&ifOutOctets, and
another session measuring ifHCInOctets&ifHCOutOctets.
The attached graph shows the MRTG traffic graph, and the two STG graphs.
Neither STG graph has a spike, but MRTG does. Where is it coming from?

(See attached file: Spike.jpg)

Any pointers/suggestions/solutions appreciated

Regards
Peter Glanville
Network Analyst, ICtS, Canon (UK) Ltd



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