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Performance and Fault Management by James M. Thompson, Kent J. Phelps, Robert L. Pavone, Christopher E. Elliott, Paul L. Della Maggiora

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VLAN/Spanning Tree

This section answers questions concerning VLANs and spanning tree on Cisco Catalyst IOS devices.

How Do I Collect VLAN Utilization?

There is no good way to collect VLAN utilization, for the following reasons:

  • Not all switch ports in a VLAN see all traffic in the VLAN.

  • Not all traffic for a VLAN traverses trunk ports.

  • Not all traffic for a VLAN hits a switch backplane.

Therefore, there is no single point at which you can measure traffic to accurately reflect the aggregate bandwidth consumed for a VLAN.

There are more useful methods for measuring capacity consumption. For instance, measuring broadcast and multicast traffic from a specific port can provide a benchmark for rising capacity needs. For a VLAN, this method is useful ...

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