Refer to the exhibit. How was spanning-tree configured on this interface?

Question

Exhibits

Options

• ABy entering the command spanning-tree portfast trunk in the interface configuration mode.
• BBy entering the command spanning-tree portfast in the interface configuration mode
• CBy entering the command spanning-tree mst1 vlan 10,20,30,40 in the global configuration mode
• DBy entering the command spanning-tree vlan 10,20,30,40 root primary in the interface

• A
  87% (58)
• B
  3% (2)
• C
  1% (1)
• D
  9% (6)

Explanation

Explanation

Option A is correct because when a switch interface is configured as a trunk port, the standard spanning-tree portfast command alone is rejected by IOS - you must explicitly append the trunk keyword (spanning-tree portfast trunk) to enable PortFast on a trunk interface, which is what the exhibit's output reflects.

Option B is wrong because spanning-tree portfast (without trunk) only applies to access ports; using it on a trunk port generates a warning and may not take effect, and the exhibit clearly shows a trunk configuration. Option C is incorrect because spanning-tree mst1 vlan 10,20,30,40 is not a valid IOS command syntax - MST instance-to-VLAN mapping uses spanning-tree mst configuration mode. Option D is wrong because spanning-tree vlan ... root primary is a global configuration command used to set the root bridge priority, not an interface-level PortFast command.

Memory Tip: Think "Trunk needs the trunk keyword" - any time PortFast is applied to a trunk port, IOS demands you explicitly acknowledge it by adding trunk to the command, preventing accidental misconfigurations.

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