[mrtg] Re: Use of MRTG+RRD for LAN traffic analysis with one second interval

kelsey hudson khudson at tsss.org
Tue Oct 11 17:11:06 MEST 2005

Prasad Kularatne wrote:
> I am currently doing a research to find out the sensitivity of Database 
> and Web traffic to iSCSI traffic in a LAN environment. 
> I do need a traffic analysis and graphing tool to peep through the TCP 
> traffic behavior on my Cisco switch.
> I am planning to use MRTG+RRD tool for this purpose.
> The documentation I went through clearly indicates that MRTG along can 
> only give me bandwidth utilization statistics in 5 minutes intervals and 
> also Florin's "MRTG Implementation Manual" also indicates that even with 
> RRD I can obtain only that granularity.
> But some of my collegues were claiming that MRTG+RRD can allow me to do 
> the traffic analysis with one second intervals.
> Therefore I thought of resolving this with the person who wrote the tools. 
> Can any one of you let me know whether the combination of the above tools 
> allow me to capture and graph traffic statistics at one second intervals. 
> As per Toby it required hacking the MRTG code. Have anyone of you done 
> this?

Although what you're asking to do isn't so difficult, polling traffic 
once per second could cause the SNMP agent on your switch to utilize far 
more CPU time than you anticipate, thereby decreasing overall switch 
bandwith and switching speed. So, your results may very well not be 
accurate if you poll them so frequently. But, if you have a beefy enough 
switch, like a 6509, it may be able to handle the extra load without 
complaining too much.

good luck.

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