[mrtg] How mrtg counts used bandwith?

Matthew Petach mpetach at yahoo.com
Fri Nov 28 18:48:02 CET 2008

This is why you want to add ::::2 to your targets so
that MRTG uses 64-bit counters instead of 32-bit
counters; with 64-bit counters, you have no roll-over

To turn on 64-bit coutners with cfgmaker, add
to the list of options you specify for cfgmaker.


----- Original Message ----
From: Alexey V. Panfilov <mrtg at subnets.ru>
To: mrtg at lists.oetiker.ch
Sent: Friday, November 28, 2008 4:08:53 AM
Subject: [mrtg] How mrtg counts used bandwith?

Hi everyone!

I've the question: how mrtg counts used bandwidth of high-loaded ports?

AFAIK, mrtg uses ifInOctets.PORT_NUM and ifOutOctets.PORT_NUM OIDs.
For example, I've Cisco3560G and I got next result:
IF-MIB::ifOutOctets.10128 = Counter32: 1751739669
but Counter32 can have maximum value of 2^32-1.
So, if I've traffic around 1Gbit/sec on this port Counter will reset to 
zero around 30 sec, but mrtg collects data every 5 min...

Please, explain me mrtg's algorithm...

P.S. Sorry for bad english

Best regards, Alexey V. Panfilov
ICQ: 1053180
Jabber: lehis at jabber.ru
mailto: ports at subnets.ru
www: http://www.subnets.ru

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