Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
Exhibit
show spanning-tree summary Switch is in pvst mode Root bridge for: VLAN0001 VLAN0010 VLAN0020 Extended system ID is enabled Portfast Default is disabled show spanning-tree vlan 40 Spanning tree enabled protocol ieee Root ID Priority 327...
A switch stack uses Rapid PVST+. Users on VLAN 40 lose connectivity for roughly 30 seconds every time the uplink on SW2 flaps. Based on the exhibit, which change would most directly improve convergence for this VLAN?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
Configure spanning-tree mode rapid-pvst.
Rapid PVST+ is the direct fix for slow STP convergence in this case.
B
Distractor review
Increase the bridge priority on SW2 for VLAN 40.
That changes root election, not the underlying convergence speed shown here.
C
Distractor review
Disable PortFast on all access ports.
PortFast is for edge ports and is not the cause of the 30-second reconvergence.
D
Distractor review
Convert the uplink to a routed port.
That changes the design, but the exhibit specifically points to STP mode.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is selecting options that change the root bridge election or port roles, such as increasing bridge priority, assuming this will speed up convergence. While root bridge placement affects path selection, it does not reduce the inherent delay caused by legacy STP timers. Another trap is disabling PortFast on access ports, which only affects edge port transitions and does not influence uplink link flap recovery times. Additionally, converting uplinks to routed ports changes the network design and removes STP from those ports, which is not the intended solution for VLAN-specific STP convergence delays. The key mistake is confusing topology optimization with protocol speed improvements.
Technical deep dive
How to think about this question
Spanning Tree Protocol (STP) prevents Layer 2 loops by blocking redundant paths and allowing only one active path between switches. The original IEEE 802.1D STP uses a slow convergence process, requiring ports to pass through listening and learning states before forwarding, which can take 30 to 50 seconds. Rapid PVST+ is Cisco's enhancement that runs a separate instance of STP per VLAN and uses a proposal/agreement handshake to reduce convergence time to a few seconds. This is critical in environments with VLAN segmentation, as each VLAN can recover independently and faster from topology changes. When a link flap occurs on a switch uplink, legacy STP causes all affected VLANs to undergo slow topology recalculations, resulting in noticeable downtime. Rapid PVST+ improves this by quickly electing port roles and transitioning ports to forwarding state without waiting for timers to expire. Enabling spanning-tree mode rapid-pvst on all switches ensures that VLAN 40 and others benefit from this rapid convergence. This mode is configured globally and affects all VLANs, replacing the default slower STP mode. A common exam trap is confusing root bridge election changes with convergence speed improvements. Increasing bridge priority only influences which switch becomes root but does not reduce the time STP takes to converge after a topology change. Similarly, disabling PortFast affects edge port behavior and does not impact uplink convergence. Converting uplinks to routed ports removes them from STP but alters network design and is not a direct fix for VLAN-specific STP convergence issues. Understanding these distinctions is essential for correctly troubleshooting and optimizing STP in Cisco networks.
KKey Concepts to Remember
- Rapid PVST+ provides faster convergence than legacy IEEE 802.1D STP by using proposal and agreement handshakes to quickly transition ports to forwarding state.
- Each VLAN in Rapid PVST+ runs a separate instance of Spanning Tree Protocol, allowing independent topology changes and faster recovery per VLAN.
- Legacy STP can cause up to 30-50 seconds of downtime during topology changes due to its slower listening and learning states.
- Switches running Rapid PVST+ use Bridge Protocol Data Units (BPDUs) to negotiate port roles and rapidly converge after link failures.
- Configuring spanning-tree mode rapid-pvst globally enables all VLANs to benefit from rapid convergence instead of defaulting to slower STP.
- PortFast is designed to speed up port transitions on edge ports but does not affect convergence time for VLAN uplink failures.
- Changing bridge priority affects root bridge election but does not improve the fundamental convergence speed of the spanning tree protocol.
- Converting an uplink port to a routed port removes it from STP but changes network design and does not directly address VLAN-specific STP convergence.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
Rapid PVST+ provides faster convergence than legacy IEEE 802.1D STP by using proposal and agreement handshakes to quickly transition ports to forwarding state.
What is the correct answer to this question?
The correct answer is: Configure spanning-tree mode rapid-pvst. — The output shows VLAN 40 is still using the legacy IEEE STP process, which converges much more slowly than Rapid PVST+. Moving the switch to rapid-pvst mode gives VLAN 40 the faster proposal/agreement behavior that typically cuts convergence time from tens of seconds to a few seconds.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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