[mrtg] Re: Max value for MaxBytes

Daniel J McDonald dan.mcdonald at austinenergy.com
Mon Apr 28 19:07:57 MEST 2003

On Mon, 2003-04-28 at 10:28, Norm Cook wrote:
> I've been using the windows implementation of mrtg (2.9.1) to get a
> cumulative count of bytes input/output on a cisco router. 

That's pretty old code - why not get the most recent from the website?

>  Cisco says max is value for counter is 2^32 - 1. 

Yes, it's a 32 bit counter.  But that is not the function of maxbytes. 
Maxbytes is supposed to be largest reasonable number that would be
expected.  If the number is vastly over that, it is assumed to be
erroneous data.  If the number is negative, then it tried to determine
is a counter-rollover could have taken place.

>  If I put this value in MaxBytes and AbsMax, my graphs show nothing. 

Right, since you essentially put -1 in.

>  If I drop this value to 2^31 -1 I get data, but of course eventually
> the data surpasses this number.

Depending on the interface, very quickly, to the point that it is
worthless.  There are a number of "totalizer" scripts out there that
will generate the data that you really want much more effectively.

>   I suspect an internal limit on MaxBytes, but can't find it doc'd
> anywhere. 

There was a discussion about it in this newsgroup not too long ago. 
Some people running 8-port GigEtherChannel or 10GigEthernet were having
trouble setting maxbytes correctly.  I believe that got fixed in 2.9.27
or so, but I haven't needed to deal with that yet, so I haven't dug
through the release notes in depth.

Daniel J McDonald, CCIE 2495, CNX
Austin Energy

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