The network shown in the exhibit was designed to provide reliability through redundancy. Both of
the IDF switches, S3 and S4, are connected to both of the MDF switches, S1 and S2. Which
configuration scenario will provide a loop-free switching environment?

A.
Spanning Tree Protocol should be running on all switches.

B.
Spanning Tree Protocol should be running on only the IDF switches S3 and S4.

C.
Spanning Tree Protocol should be running on only the MDF switches S1 and S2.

D.
Spanning Tree Protocol should be run only on the root bridge.

E.
Spanning Tree Protocol is not needed in this network.

Explanation:
Spanning-Tree Protocol (STP) prevents loops from being formed when switches or bridges are
interconnected via multiple paths. Spanning-Tree Protocol implements the 802.1D IEEE algorithm
by exchanging BPDU messages with other switches to detect loops, and then removes the loop by
shutting down selected bridge interfaces. This algorithm guarantees that there is one and only one
active path between two network devices.
Reference:
http://www.cisco.com/en/US/tech/tk389/tk621/tsd_technology_support_protocol_home.html