[mrtg] What default OIDs are used by MRTG?

Alex van den Bogaerdt alex at ergens.op.het.net
Tue Mar 18 03:39:47 CET 2008

On Mon, Mar 17, 2008 at 08:42:30PM -0400, James Geiger wrote:
> Thanks all for the responses.
> With the in and out octets, does anyone know the magic (formula) that MRTG
> uses to convert it to a number that makes sense?  When I do an snmpget on
> any particular device for those two OIDs it returns some crazy number up in
> the billions.  MRTG converts it to something (for example) like 2MB/s or
> what have you.  Is the formula also done in perl or are there other internal
> conversion scripts to make it so its readable by your average human?

Compare to other counters, such as:
- electricity
- gas
- water
- heat
- car mileage

All these counters just keep counting up.

Note the value at time 't1', for instance 123456789 at 1:00pm
Note the value at time 't2', for instance 123467589 at 2:00pm

Compute their differences:

t2:  2pm 123467589
t1:  1pm 123456789
     ------------- -
diff 1hr     10800    That's 10800 per hour, thus 3 per second.
rate between 1pm and 2pm: 3

MRTG uses rateup to do this job, or, if you use RRDtool, it is
RRDtool which does this job.

Above example is for regular counters.  Other methods do exist:
- gauge: these numbers are already a rate, use them

t2:  2pm         3
t1:  1pm         x (not important for this example)
     no computation
Rate between 1pm and 2pm: 3

- absolute: these counters are reset every time you read them

t2:  2pm     10800
t1:  1pm         x (not important for this example)
diff 1hr     10800
rate between 1pm and 2pm: 3

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