# [mrtg] Re: mathematical expressions for Collision statistics

Tom McGovern tom at mcgov.net
Tue Nov 6 18:29:41 MET 2001

```Can someone help me troubleshoot my formula below:

Target[6-col.192.168.254.127]:
(1.3.6.1.2.1.16.1.1.1.13.106:public at 192.168.254.127 /
1.3.6.1.2.1.16.1.1.1.5.106:public at 192.168.254.127) * 100 &
(1.3.6.1.2.1.16.1.1.1.13.106:public at 192.168.254.127 /
1.3.6.1.2.1.16.1.1.1.5.106:public at 192.168.254.127) * 100

This is the error I get from mrtg =

Target[6-col.192.168.254.127]: eval warning: Illegal division by zero at
<eval 89> line 1

However, neither of my polled values are of a zero value !

Tom

-----Original Message-----
From: Foverskov, Esben, esf [mailto:esf at esbkomm.dk]
Sent: Tuesday, November 06, 2001 10:54 AM
To: 'Tom McGovern'; mrtg at list.ee.ethz.ch
Subject: RE: [mrtg] mathematical expressions for Collision statistics

Hi,

Don't quite know whether the formula would work, but is this really what you
want? the etherStatsCollisions counts the number of collisions that have
occurred, right? And you are dividing this by the total number of bytes in
and out the interface. That doesn't make sense. So looking at the units
only, you're dividing packets with bytes, giving you the unit packets/byte.
You need to divide packets with packets to get a percentage (no units). How
you would go about doing that is another question entirely ;O)

-----Oprindelig meddelelse-----
Fra: Tom McGovern [mailto:tom at mcgov.net]
Sendt: 6. november 2001 16:24
Til: mrtg at list.ee.ethz.ch
Emne: [mrtg] mathematical expressions for Collision statistics

Hi,

I'm trying to measure the amount of ethernet collisions as a percentage of
the overall interface traffic. I think this is what I want:

Target[13-col.192.168.254.127]:etherStatsCollisions.113:public at 192.168.254.1
27 / ifOutOctets.113:public at 192.168.254.127 +
ifInOctets.113:public at 192.168.254.127 &
etherStatsCollisions.113:public at 192.168.254.127 /
ifOutOctets.113:public at 192.168.254.127 +
ifInOctets.113:public at 192.168.254.127

Note I am just graphing the same variable twice fo simplicity.

But, how will MRTG interpret this formula ? Can I use parentheses in my
formular ?

Basically I need the following:

etherStatsCollisions / (ifInOctets + ifOutOctets) * 100

Thanks,

Tom McGovern

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