On Mon, Jun 28, 2010 at 10:23:29PM -0300, Martin Parodi wrote:
>    Thanks again Craig, now you solved part of the problem, but I continue
>    with the problem but now on all interfaces traffic, just a few interfaces.
>    The strange issue is that I cant see only vlan interfaces traffic graphs,
>    but gigabit or fastethernet interfaces are working fine.
Sounds like a Cisco switch.
Certain switches do not report the correct amount of traffic on vlan
interfaces.  It's a "feature" of the switch rather than JFFNMS (or
mrtg). Even the "show interfaces"  command gives the wrong number.

I recall seeing this issue back in the early 90s.  A quick google of
phrases like mrtg and vlan shows it still a problem.

In short: cisco + vlan = bad counters

I'd hate to think of the number of network engineers that have torn
their hair out about this bug, you look at the vlan interface, you look
at the physical interface... "but but the traffic must be going
SOMEWHERE!"

Deep down in the Cisco documents somewhere it probably explains it, but
like most Cisco documents you can never find them!

 - Craig

-- 
Craig Small      GnuPG:1C1B D893 1418 2AF4 45EE  95CB C76C E5AC 12CA DFA5
http://www.enc.com.au/                             csmall at : enc.com.au
http://www.debian.org/          Debian GNU/Linux, software should be Free 

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