[mrtg] Re: two questions

Peter Glanville peter_glanville at cuk.canon.co.uk
Wed Feb 19 11:52:31 MET 2003

1.) I want to do a self monitoring. If the monitoring machine is up, it
will return 1; otherwise (e.g no network, reboot, power off) it will return
0. I try to do this by monitoring the operational status of loopback
( .iso.org.dod.internet.mgmt.mib-2.interfaces.ifTable.ifEntry.ifOperStatus
). However, it always return 1. Which thing should I monitor so as to
fulfil my purpose?

If your system is down, how will it be able to monitor itself???
When it is up and running, and able to check, it returns a 1 to say it is
The solution is to monitor it from another box.

2.) I use Linux to monitor a few routers' traffic. I found something
strange: e.g If my linux is down for about 30 minutes, and then up again, I
found that the traffic value will have a surge and then back to normal
again :

MRTG compares the current value with the previous value, and divides by
time, to calculate rate.
Even if you do not retrieve the values for 30 minutes, the meter still
counts up, and so when you do retrieve another value, it has jumped
massively, and a high rate is calculated.
This might be ignored by MRTG, if it exceeds the value defined by Maxbytes.
The surge is spread over a short time period because of Normalisation.

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