[mrtg] Re: Network Bandwidth

[Steve Shipway]

>Can someone advise or help me on the following question from 
>my boss, what would be the best way to monitor this?
>"Deb, have you made any progress in detecting bandwidth usage 
>outside a norm?"  Can MRTG help me here?
As Andi says, first find what the norm actually is.  If you collect stats
from MRTG for at least a week (probably a month would be better) then you
can get a good baseline.  This will allow you to pick a 'normal' range, and
a level which you would want to be alerted to.

I would suggest you use the 95th Percentile as a good indicator of normal
usage -- 95% of the time, usage is below this level.  Alternatively, use the
Maximum Peak value (ie, the 100th Percentile value).  You can get the 95th
percentile from MRTG (routers2.cgi (see web site in sig) will give it to
you, but there are other tools also).  All frontends will give you Max Peak
values.

Pick a threshold either based on avaiable bandwidth (alert at 95% usage), or
on normal ranges (alert when usage exceeds the 95thPercentile value, etc).
Make sure you don't pick too low a threshold and alert too often -- too many
false positives make an alerting tool useless.

Then, you can set a Threshold on your MRTG .cfg file to alert you (or to
log, or whatever) when the value passes your 'norm' level. Nagios is a good
thing to use for alerting, and it can also take stats from MRTG if required.

Alternatively, keep daily records of the 95th Percentile, and use this to
show overall usage trends.

Steve

---
Steve Shipway: ITSS, University of Auckland
Email: s.shipway at auckland.ac.nz  Web: http://www.steveshipway.org/software/

** We can only discover new oceans when we have the **
** courage to lose sight of the shore.              **


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