In what situation must spanning-tree be implemented?

In what situation must spanning-tree be implemented?
A . when first hop redundancy protocol exists with redundant Layer 2 links between distribution switches
B . when a VLAN spans access layer switches to support business applications
C . when trunks need to extend multiple VLANs across access switches
D . when it is necessary to speed up network convergence in case of link failure

View Answer

Answer: A

Explanation:

Previous answer was “B” but that has now been changed to “A”.

STP (L2 loop prevention mechanism) should be implemented in topologies where possible loops may occur and redundant L2 links between distribution switches is a very good example as long as the links are not channelled (PC, vPC, MEC). If the redundant L2 links between distribution switches are channelled, the topology is loop free so no STP is required but the doesn’t say anything about that.

With regards to answer “A”, VLAN can be stretched between multiple access switches via distribution layer and still be loop free so (know from experience).