[mrtg] Re: links addition not working fine !!

[Daniel J McDonald]

On Mon, 2004-02-09 at 07:29, Mohamed Eldesoky wrote:
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> Hi, 
> 
> I am using mrtg with rrdtool to monitor the network routers.
> I am trying to sum the total bandwidth used in the backbone links.
> 2 of the links run off a cisco, the third runs off a Juniper.
> The individual links graph fine, but when trying to add them up, using the 
> normal mrtg "+", it works fine half of the day, and the other half (during 
> activity time) it just shows near zeros and near maximum (alternatively, like 
> a jigsaw shape !!)

Yup.  A consequence of counters rolling over and MRTG not being able to
detect it, since you might have two (or three!) of them rolling at any
one time.  So, instead of just adding 2^32 for the roll-over calc, mrtg
would have to add 2^33.  You can mitigate that by polling 64-bit
counters using the version syntax, but the underlying problem remains.

You would be better off with three separate targets, and then using some
hacks in routers.cgi to combine them.
-- 
Daniel J McDonald, CCIE 2495, CNX
Austin Energy


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