[mrtg] Graphing over 100% of MaxBytes?

Rodolfo J. Paiz rpaiz at simpaticus.com
Fri Oct 15 17:55:46 MEST 2004

Hello, everyone:
This is my first post to this list, and I have very little experience
with MRTG, so bear with me if I missed something obvious. I *have* spent
a fair amount of time in RTFM/STFW but haven't solved my problem.

I'm running MRTG (2.10.5-3) from the RPM package supplied with Fedora
Core 2 on a five-interface router/firewall box like this:

eth0 (to the Internet)   512 Kbps    MaxBytes[64000]
eth1 (to Customer #1)    128 Kbps    MaxBytes[16000]
eth2 (to Customer #2)    256 Kbps    MaxBytes[32000]
eth3 (to Customer #3)    256 Kbps    MaxBytes[32000]
eth4 (to Customer #4)    128 Kbps    MaxBytes[16000]

If I strictly limit each customer's bandwidth to what they purchased,
everything is great and the MRTG graphs are totally accurate. But... now
I've made a local mirror of the Fedora Core updates; with ~40 machines,
it saves the whole building a ton of bandwidth.

I've allowed the customers to use the full 100 Mbps to the firewall, and
only limit them to 128/256 Kbps for traffic *through* the firewall out
to the Internet. But now the MRTG graphs break in one of two ways:

  1. If I set MaxBytes[12500000] for 100 Mbps, then 128 Kbps becomes
0.1% of their maximum allowed bandwidth and the percentage utilization
numbers become all but useless.

  2. If I leave MaxBytes[16000] for 128 Kbps, then any traffic above
that number overloads the counters in MRTG, and the graphs and
percentages show the modulus of the actual bandwidth consumed and the
bandwidth contracted. That is, pushing 160 Kbps through a line where
MaxBytes is set for 128 Kbps will actually show and graph 32 Kbps (mod
[160,128]). This is worse, since now I have *no* idea of what
happened... it could mean 160 Kbps, 288 Kbps, or any multiple above.

Sorry for such a long post, but: Is there any way to tell MRTG that the
*link capacity* is 100 Mbps, but that I want percentages calculated as a
percentage of 128 Kbps? So that pushing 192 Kbps through the link would
show a bandwidth utilization of 150%?

Thanks for any advice you can offer,

Rodolfo J. Paiz <rpaiz at simpaticus.com>

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