Chapter 4. Multiple Spanning Tree Protocol

Which of the following issues does MST solve? (Choose two.)

• Enables traffic load balancing for specific VLANs

• Reduces the CPU and memory resources needed for environments with large numbers of VLANs

• Overcomes MAC address table scaling limitations for environments with large numbers of devices

• Detects issues with cabling that transmits data in one direction

• Prevents unauthorized switches from attaching to the Layer 2 domain

Answer explanation

MST enables traffic load balancing for specific VLANs through assignment of VLANs to specific instances that might have different topologies. MST also reduces the amount of CPU and memory processing as multiple VLANs are associated with an MST instance.

With MST, VLANs are directly associated with ______.

• areas

• regions

• instances

• switches

Answer explanation

VLANs are associated with MST instances, and an instance defines the Layer 2 forwarding topology for the VLANs that are associated to it.

What do CST and 802.1D have in common?

• They support only one topology.

• They support multiple topologies.

• They allow for load balancing of traffic across different VLANs.

• They provide switch authentication so that inter-switch connectivity can occur.

Answer explanation

The original 802.1D specification accounted for one topology for all the VLANs, and Common Spanning Tree (CST) uses one topology for building a loop-free topology.

True or false: The MST root bridge advertises the VLAN-to-instance mappings to all other MST switches.

• True

• False

Answer explanation

False. MST uses an internal spanning tree (IST) to advertise itself and other MST instances for building the topology. The local switch configuration associates VLANs to the MST instances.

True or false: The MST configuration version is locally significant.

• True

• False

Answer explanation

False. The MST configuration is relevant to the entire MST region and should be the same for all switches in the region.

True or false: The MST topology can be tuned for root bridge placement, just like PVST+ and RSTP.

• True

• False

Answer explanation

True. The MST topology can be tuned by setting priority, port cost, and port priority for each MST instance.

MST regions can interact with PVST+/RSTP in which of the following ways? (Choose two.)

• The MST region is the root bridge for all VLANs.

• The MST region is the root bridge for some VLANs.

• The PVST+/RSTP topology is the root bridge for all VLANs.

• The PVST+/RSTP topology is the root bridge for some VLANs.

Answer explanation

MST can interact with PVST+/RSTP environments by acting as a root bridge for all VLANs or ensuring that the PVST+/RSTP environment is the root bridge for all VLANs. MST cannot be a root bridge for some VLANs and then let the PVST+/RSTP environment be the root bridge for other VLANs.