[rrd-users] Re: Problem with MRTG and RRDTool

Chris Wilson chris at aidworld.org
Sun Sep 11 14:39:42 MEST 2005

Hi Emmanuel,

> Im having problems graphing a Giga bandwidth. My traffic is reaching 700 
> Mbps. But MRTG is just displaying about 70Mbps. I hit a wall on his one. I 
> check the RRD of my mrtg element and the data is reall 70Mbps. But on the 
> remote router it says 700Mbps, through a trhoughput test (iperf).
> I hope you can give me hints on how to resolve this one.

I think that iperf is measuring throughput in bits per second, and mrtg
in bytes per second. The difference should be a factor of 8, not 10, but
that might be a bug in iperf.

Unless you have a 10 gigabit network, you cannot put 700 megabytes of
data per second through it (and even then you would need some very
special hardware). Routers normally measure throughput in bytes, not
bits, since they can't forward a fraction of a byte. So I wouldn't be
surprised if mrtg measures throughput in bytes per second, because it's
asking the router (or the ethernet interface, which behaves the same

Iperf cannot measure bits on the wire either, so it must be making an
assumption about how many bits go onto the wire to send a single byte,
to report a speed in bits per second.

Hope this helps.

Cheers, Chris.
(aidworld) chris wilson | chief engineer (chris at aidworld.org)

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