[mrtg] Odd MRTG Behaviour

[Jason Jordan]

Howdy Folks,

I have a switch on which I wish to add 3 interfaces together.

When you graph each interface - what appears to be the correct volume of
data is drawn.

However, when you perform:
target[foobar]: 1:public at 192.168.1.1 + 2:public at 192.168.1.1 +
3:public at 192.168.1.1

The graph appear to show less data than the sum of the three graphs
drawn individually.

I suspect that MRTG does the following:

MRTG adds all the interfaces together and then calculates the difference
from the previous collection.  Considering any of these 100mbit
interfaces may have reached the 32bit rollover, adding in this manner is
likely to generate inaccurate results.

What I think MRTG should do:

Calculate the difference for each interface, then add them together.  In
this way it would be far easier to calculate when a 32 bit rollover has
occured.

Could someone verify this?  I have a specific need for this
functionality and I'm postive someone must have come across this before!

Cheers, Jas

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