Burton and Chris are correct.  

Many thanks.

Andrew


-----Original Message-----
From: Burton Strauss [mailto:[EMAIL PROTECTED]
Sent: Friday, August 05, 2005 1:14 PM
To: [email protected]
Subject: RE: [Ntop] VLANs and NTOP


Well, that's probably your problem.

Think basic switch logic: What is sent out a trunk?  Only those packets
which the switch knows need to - which would be learned MAC addresses on
that port and broadcasts...

-----Burton

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of
Willy, Andrew
Sent: Friday, August 05, 2005 1:50 PM
To: '[email protected]'
Subject: RE: [Ntop] VLANs and NTOP

Error in this post.  Not using Cisco SPAN.  Span is how I mirrored whatever
VLAN to the ntop box.  Now it is trunk port.

Andrew

-----Original Message-----
From: Willy, Andrew [mailto:[EMAIL PROTECTED]
Sent: Friday, August 05, 2005 11:16 AM
To: '[email protected]'
Subject: RE: [Ntop] VLANs and NTOP


After reading this I tapped a trunk port.  ntop obligingly began picking up
VLAN tags, but the traffic statistics aren't correct.  All the expected
hosts appear but are reported as sending and receiving far less than when
listening to an access port.  

For example, a host on VLAN 20 that on average moves a gig or so on hour has
its traffic properly reported by ntop when the sensor is listening just to
VLAN 20.  When listening to a trunk port that includes VLAN 20, the host is
seen but ntop only reports the host having moved 500k in the last three
hours (which I know to be incorrect.)

Thought I may have overwhelmed the little box ntop is running on, but I
don't see that it has dropped any packets.  Is it possible the NIC can't
keep up?  There is 250+ hosts transmitting on the vlans being monitoring.
Using Cisco SPAN on a 100mb link.

Andrew

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