[mrtg] Re: OT Bandwithd

[Matthew Petach]

--- Alfred Payne <alfred at tcsn.co.za> wrote:
> 
> ----- Original Message ----- 
> From: "Matthew Petach" <mpetach at yahoo.com>
> To: "Alfred Payne" <alfred at tcsn.co.za>; <mrtg at list.ee.ethz.ch>
> Sent: Monday, September 20, 2004 7:07 PM
> Subject: [mrtg] Re: OT Bandwithd
>  
> > 
> > --- Alfred Payne <alfred at tcsn.co.za> wrote:
> > > Hello Everybody,
> > > 
> > > Am I allowed to post questions
> > > regarding another bandwidth
> > > monitoring tool that I'm running
> > > on my Linux box called "bandwidthd"?
> > > 
> > > if "yes" then
> > >     
> > >     What I want to know is,if my monitoring box
> > >     is just another node in the network i.e all traffic
> > >     does not necessarily route through or past it,can
> > >     I expect reliable traffic reports? My interface is
> > >     in promiscuous mode,but I'm not sure if I'm scoring
> > >     all the traffic;
> > > 
> > > else
> > > 
> > >     Apologies for wasting your time;
> > > 
> > > -A
> > > 
> > 
> > Short answer is that no, you can't count on seeing all the
> > traffic that way, unless your network consists of an entirely
> > flat topology, eg all hosts plug into a common hub (not a 
> > switch).
> > 
> > Matt
> > 
> 
> Because of ARP request I figure....
> If I can fool all my hosts into 
> thinking that I'm the "default gateway"
> it would be a different story,right?
> 
> Alf

Well, why bother trying to "fool" them?  Why not just turn on
ip_forwarding in your kernel, and set all the other hosts to
use your IP address as their default gateway for real, if you
want to be able to measure and track all traffic leaving your
network?  (Note that even with this setup, you'll only see the
traffic leaving your subnet; traffic between hosts will still
be switched directly between them without hitting your host.

In general, if you have a flat hub-only network, you can get
away with putting your host in promiscuous mode and just
listening to everything.  If you have any switch ports in your
network, the only way to get true traffic stats is to monitor
the switch directly using SNMP, TL1, or some other management
protocol.

Matt

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