[mrtg] Re: configure mrtg for a 1000M network router

Alex van den Bogaerdt alex at ergens.op.het.net
Wed May 12 16:56:46 MEST 2004

On Wed, May 12, 2004 at 10:21:55PM +0800, George Lin wrote:

> I am assigned a task to configure mrtg for a 1000M network router. I have 
> some experiences before to configure mrtg to monitor a 100M network router, 
> so the basic configuration is not a problem. But a friend told me that mrtg 
> can not work smoothly with high speed network (for example, 1000M network) 
> without snmp V2 enabled and rrdtool enabled. And the interval mrtg script 
> runs should be 1 minute (as short as possible). I previously use 5 minute 
> interval in crontab to enable mrtg to monitor 100M router.

You're dealing with the problem of counter overflows.  This can happen
in the snmp counters and can also happen in the mrtg programs.

Using 64-bit counters will solve at least one problem, that of snmp
counters overflowing.

When the counter values are coming in using 64-bit counters, mrtg should
be able to cope with them.  The resulting rate (after computing the diff
and dividing by the diff in time) may exceed the amount that can be
stored in a 32-bit counter.  I am not sure if MRTG can cope with data
rates above 2 GB/s.

Running MRTG every minute in stead of every 5 minutes will result in:
- smaller deltas inbetween updates (useful for 32-bit counters)
- more granularity in detecting peak values

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