Refer to the exhibit. Which two commands ensure that DSW1 becomes root bridge for VLAN 10 and 20?

Question

Exhibits

Options

• Aspanning-tree mst 1 priority 1
• Bspanning-tree mst 1 root primary
• Cspanning-tree mstp vlan 10,20 root primary
• Dspanning-tree mst vlan 10,20 priority root
• Espanning-tree mst 1 priority 4096

• A
  5% (2)
• B
  82% (32)
• C
  10% (4)
• D
  3% (1)

Explanation

Explanation

In Multiple Spanning Tree (MST), VLANs are mapped to MST instances, so if VLANs 10 and 20 are mapped to MST Instance 1, you configure priority on that instance - not on the VLANs directly. Option B (spanning-tree mst 1 root primary) automatically sets the priority to 24576 (or lower if needed) to win root election for MST instance 1, and Option E (spanning-tree mst 1 priority 4096) manually sets a low priority value (4096 is a valid multiple of 4096 and low enough to win), both correctly targeting MST instance 1.

Why the distractors are wrong:

• A is incorrect because priority 1 is not a valid priority value - MST priorities must be multiples of 4096 (e.g., 0, 4096, 8192).
• C is incorrect because mstp is not valid IOS syntax, and MST does not use vlan in the command - you reference the instance number.
• D is incorrect because priority root is not valid syntax; the correct form is either root primary or a numeric priority value.

Memory Tip: Think "MST = Instances, not VLANs" - always configure MST spanning-tree commands using the instance number, and remember priorities must be multiples of 4096 (0, 4096, 8192...).

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