[mrtg] Re: Newbie

Bill Wichers billw at waveform.net
Thu Sep 5 02:30:20 MEST 2002

If you know the maximum available capacity of a circuit, you can determine 
what is left by figuring the max - the shown use and get the remaining 
capacity. MRTG automatically presents this as a percentage if you set 
MaxBytes[] appropriatly for the interface you are monitoring. 

An example for a fast ethernet interface (100 Mb/s / 12.5 MB/s) 

Target[int]: int_no:comm_name at router_IP
Title[int]: some interface
PageTop[int]: <h1>some interface</h1>
MaxBytes[int]: 12500000
Options[int]: growright,bits  ### I got programmed to read "new on the 
right" by a stats grapher I used before MRTG, and we measure serial 
interfaces in bits ### 

The MaxBytes tells MRTG the max available capacity of the interface in 
question and is used in the percent calculations. MRTG will also draw a red 
horizontal line on the graphs if your traffic scales the graphs enough that 
it will show on the scale. 

Now if you're asking about _ports_ and not _bandwidth_ available, I guess 
you'd just need to graph all the ports and assume no traffic = a free port. 
You could probably find something buried in the SNMP mibs that would let you 
graph the status of a link too if you wanted too, but there are other 
management tools better suited to that sort of thing. 


Bruce Conmee writes: 

> Hello,
> This may sound silly but, how can I determine from the stats that MRTG is
> producing whether or not I have any available capacity on my swithces and
> routers?
> Thanks

Waveform Technology
UNIX Systems Administrator 

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