Cisco VLAN Traffic Statistics

[Matt]

When you look at traffic stats for a physical interface input is obviosuly from the downstream device and output is what is going to the downstream device. (I am basing this from a core switch perspective).

With a VLAN I take it that output traffic shows the total going to ALL ports within the VLAN and this may include trunk ports from which a VLAN has nto been pruned and will of course include the etherchannel between 2 core devices. Similarly for input traffic, that will be coming from many sources, WAN, user stcks and so forth. I am also of the view that the figures would include traffic between devcies within the VLAN, say two servers talking to each other.

This would explain why when I graph the data for my production server VLAN I see peak values of 120%, against what I take to be a notional 1 Gbps - given its 6509 - with 4 blades of 1 Gbps ports.

or am I way off beam here?

Cheers

[Michael McNamara]

You've stumble upon an interesting topic... the VLAN statistics for many of the Layer 2 switches only graphs packets/frames that hit the CPU. The VLAN statistics for a Layer 3 switch usually graph the IP interface for that VLAN.

If you search around you'll find a few different threads discussing the issues that people have had trying to collect the information you're looking for.

Here's one that seems like the best;http://www.experts-exchange.com/Hardware/Networking_Hardware/Switches/Q_23738165.html

Cheers!