You want to enable the IEEE 802.1w Rapid Spanning Tree Protocol (RSTP) on a Cisco switch that supports Per VLAN Spanning Tree. Which global configuration mode command should you use to configure the switch to run rapid per VLAN spanning tree (rapid-pvst)?

Introduction / Context:
Cisco Catalyst switches support different Spanning Tree Protocol (STP) modes, including the original IEEE 802.1d STP, the faster 802.1w Rapid STP (RSTP), and Cisco variations such as Per VLAN Spanning Tree Plus (PVST+) and Rapid Per VLAN Spanning Tree (rapid-pvst). To take advantage of faster convergence, many networks enable rapid-pvst mode. This question checks whether you know the correct global configuration command and context to enable 802.1w based rapid-pvst on a Cisco switch.

Given Data / Assumptions:

• The switch supports different STP modes such as pvst, rapid-pvst, and mst.
• You want to enable the rapid-pvst mode, which is Cisco's implementation of IEEE 802.1w RSTP on a per VLAN basis.
• The configuration must be done in global configuration mode, not just at an interface level.
• You are choosing from commands that are very similar in format and prompt level.

Concept / Approach:
To change the STP mode on a Cisco switch, you use the spanning-tree mode command in global configuration mode. The supported keywords include pvst, rapid-pvst, and mst. Rapid-pvst corresponds to the rapid per VLAN spanning tree mode based on 802.1w. The prompt for global configuration mode is Switch(config)#. Commands entered at the EXEC level such as Switch# without entering configuration mode will not change global STP mode. Commands that explicitly mention 802.1w instead of rapid-pvst are not valid IOS syntax for setting the spanning tree mode on most Catalyst platforms.

Step-by-Step Solution:
1. Recall that STP mode is a global setting, not an interface specific setting, so you must be in global configuration mode. 2. Recognize the global configuration prompt as Switch(config)#. 3. Remember the correct keyword for rapid STP per VLAN on Cisco devices is rapid-pvst. 4. Combine these facts to form the command: spanning-tree mode rapid-pvst. 5. Place this command at the global configuration level, giving: Switch(config)# spanning-tree mode rapid-pvst.

Verification / Alternative check:
You can confirm this behavior by recalling other possible modes. For example, to configure multiple spanning tree, you would type Switch(config)# spanning-tree mode mst. In the same pattern, rapid-pvst is the keyword used for the rapid version of PVST. Additionally, most Cisco official examples show exactly this syntax when enabling RSTP with per VLAN support. This consistency across documentation and labs confirms the answer.

Why Other Options Are Wrong:
Option b: Switch# spanning-tree mode rapid-pvst is entered from EXEC mode, not configuration mode, so it is not a valid configuration command. Option c: There is no commonly supported spanning-tree mode 802.1w keyword; the correct keyword is rapid-pvst, not 802.1w in Cisco IOS syntax. Option d: Similar to option b and c, this is EXEC mode and uses the wrong keyword, so it is not correct. Option e: Switch(config-if)# spanning-tree mode rapid-pvst would be interface configuration mode, but STP mode is not configured per interface; it is global for the switch.

Common Pitfalls:
Exam candidates often focus only on the keyword rapid-pvst and overlook the configuration context, choosing answers that show the correct keyword but the wrong prompt level. Another pitfall is confusing the IEEE standard number 802.1w with actual IOS syntax. While 802.1w describes Rapid STP, Cisco uses the rapid-pvst keyword to configure it. To avoid mistakes, always remember that global STP mode changes are done at the Switch(config)# prompt and use the exact IOS keywords defined by Cisco, not the IEEE numbers.

Final Answer:
To enable rapid per VLAN spanning tree, you should use Switch(config)# spanning-tree mode rapid-pvst.