[mrtg] Traffic (incoming, outcoming) - what does it correspond to??

Eric Brander mailinglists at rednarb.com
Thu Jul 17 22:06:08 CEST 2008

On Thu, Jul 17, 2008 at 10:22 AM, Alia <alia at femininbio.com> wrote:
> Hi guys,
> So what I'd like to know is whether the "traffic" shown in these graphs
> has anything to do with the number of people connected, the activity on
> the site, or what?  Last but not least, I'm also unclear on the
> difference between "incoming" and "outcoming" traffic.  Any help would
> be most appreciated!!


Traffic, as seen by MRTG in this scenario is simply the number of bits
traversing an interface. Higher traffic load on a web site would
usually indicate higher traffic monitored on the interface as well.
However, that truly depends on the web site. One refresh of a simple
web site might cause the back end server to barely blip as it simply
sends out the data requested once more. Half a million of those blips
start making a more noticeable yet linear impact. However, if with
each refresh the system has to do a complex query then the amount of
load on the system itself will be much higher while the actually
traffic on an interface will still be just a blip. User makes a
request. Host receives it. Host processes it. Host sends back results.
When half a million of these happen, the back-end process can really
bog down as it may have to wait for other things to complete or simply
not be an efficient enough process to scale correctly.

By watching the traffic with MRTG (as long as all things are equal and
MRTG is set up correctly) you have historical evidence that indicates
the system and the network infrastructure are capable of handling high
loads of network traffic but clearly your application is up to snuff.
Sounds to me like MRTG in this case is helping you prove that it is
NOT the network that is the bottleneck with this application. That
said - there is really too little information to make that
determination for certain of course...

As far as incoming and outgoing, think of it from the device's point
of view. Incoming would be data coming from a host connected to an
interface. Outgoing would be data leaving the interface and heading
toward the host connected.


Eric Brander

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