Several key areas relating to the performance and fault monitoring of VLANs are as follows:
Logical ports versus physical ports
VLAN Utilization based on broadcast and multicast traffic
Running spanning tree within VLANs
The logical ports calculation addresses the hardware limitation of the supervisor cards installed in the switches. The formula is documented in the Catalyst Series release notes available on CCO and is reiterated here:
Monitoring broadcasts and multicasts to determine the VLAN utilization versus monitoring unicast traffic through the switches is important. Because the purpose of VLANs is to isolate your broadcast domain, ...