200-150 Question #186: Real Exam Question with Answer & Explanation

The correct answer is D: MST is not enabled on 7k-3 and 7k-4. MST is configured but not enabled because the 'spanning-tree mode mst' command is absent on both switches.

Cisco Data Center Networking Technologies

Question

Which of the following statements is true about the network? 7K-3 and 7k-4 have the following configuration. Spanning-tree mst 1 priority 24576 Spanning-tree mst configuration name DCICN revision 2 instance 1 vlan 100-150

Options

A7K-3 is the mst root for VLANs 100-150
B7k-4 is the mst root for VLANs 100-150
CBoth 7k-3 and 7k-4 are the root for VLANs 100-150
DMST is not enabled on 7k-3 and 7k-4

Explanation

MST is configured but not enabled because the 'spanning-tree mode mst' command is absent on both switches.

Common mistakes.

A. 7K-3 cannot be the MST root for instance 1 because MST mode is not enabled - the required 'spanning-tree mode mst' command is absent from the configuration.
B. 7K-4 also cannot be the MST root because MST has not been activated with 'spanning-tree mode mst', regardless of the priority value configured.
C. Although both switches share the same priority of 24576 for MST instance 1, this is irrelevant because the MST mode activation command is missing on both devices.

Concept tested. MST mode activation vs. MST region configuration

Reference. https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus7000/sw/layer2/config/cisco_nexus7000_layer2_config_guide/config_spanning_tree.html

Topics

#MST#spanning tree#VLAN assignment#Nexus 7K

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