[mrtg] Re: VLAN monitoring at Trunk Port using MRTG

Nelson Tseung ntseung at yahoo.com.hk
Tue Apr 6 10:26:42 MEST 2004

Hi Tim

Thx again to share yr exp with me.

I think I get your point. If measurement is taken for
in/out traffic only of each VLAN at a trunk port. Then
should be alright.

However, could you tell me some ref. or URL where I
can find more details?

Because I failed to create the required config file
for VLAN bit in/out measurement on trunk port when
cfgmaker was used. In my lab test, Catalyst 5500 was
used, but Cfgmaker could only list interface either by
port or by vlan, but no vlan per port.

Do I need manual editing for such purpose?
Any clues?

 --- Tim Sheets <TSheets at illinois.net> wrote: > 
> > -----Original Message-----
> > From: Nelson Tseung [mailto:ntseung at yahoo.com.hk]
> > Sent: Friday, April 02, 2004 9:40 AM
> > To: Tim Sheets
> > Subject: RE: [mrtg] VLAN monitoring at Trunk Port
> using MRTG
> > 
> > 
> > Many Thanks to your reply.
> > 
> > Acutally, I would like to use MRTG to monitor
> traffic
> > in/out of each VLAN in a LAN Switch Trunk port.
> > 
> If you are wanting to monitor traffic in/out of the
> VLAN, that should be
> OK.  If you are trying to measure traffic *on* the
> VLAN, that's where
> you would have trouble.  Since a VLAN can include
> many ports across many
> switches, I don't know if you could get an accurate
> measure of traffic
> on the VLAN itself, or what that information could
> be used for.  I know
> when MRTG has picked up the (virtual) VLAN
> interfaces on our Cisco
> switches, the numbers haven't been all that
> interesting.  I hope I am
> explaining myself well and not confusing you.  Any
> individual port
> (regardless of trunk or access port), is easy.  The
> only thing to be
> aware of is if you are monitoring the trunk in/out,
> there could be more
> traffic that stays in the VLAN that you don't pick
> up.  But, again, all
> you probably care about is utilization levels on key
> ports (or maybe all
> if looking for compromised machines), and the trunk.
> Have a good weekend,
> Tim 

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