Before make changing in the cisco base LAN network’s topology (all switches are cisco catalyst) there is needed to enable monitoring protocols such as SNMP on them and integrate it with monitoring applications.There are 2 reasons to do this: First, during designing the new plan some traffic fault maybe happens and you can troubleshoot it soon before users call you about problem (decrease down-time of the network). Second after changing topology you can see increasing performance Parameters such as CPU usage on the switches.

Now here is one of my experiences about it:

In the network that was contains about 3000 clients and using flat network (No VLANs) I was doing VLAN design Procedure. One day I received an alarm from monitoring application about all switches  CPU usage increased to 99% and notified that network not working correctly(I have done SNMP setting and monitoring before). It means that something wrong about network traffic. Then I used “Wireshark” to find the problem. Yes it was occurred because of broadcasting WORM generated from just 1 PC in the flat LAN. After disabling the PC’s switch port, broadcasting WORM was stopped and CPU usages of all switches decrease to normal state and network began working correctly. This procedure is more important for the company that needs high availability and low down-time network operation.