Redesigning a Legacy 802.1D Layer 2 Domain

300-420 By islever Editorial Last updated

Design campus Layer 2 infrastructures

Short answer

AC Replace 802.1D with Rapid PVST+ for sub-second convergence and use VTP to propagate and prune VLANs, cutting manual configuration work.

Question

A customer's current Layer 2 infrastructure is running Spanning Tree 802.1d, and all configuration changes are manually implemented on each switch. An
architect must redesign the Layer 2 domain to achieve these goals:
  • reduce the impact of topology changes
  • reduce the time spent on network administration
  • reduce manual configuration errors
Which two solutions should the architect include in the new design? (Choose two.)
  1. Implement Rapid PVST+ instead of STP. Correct Answer
  2. Implement MST instead of STP.
  3. Use VTP to propagate VLAN information and to prune unused VLANs. Correct Answer
  4. Configure broadcast and multicast storm control on all switches.
  5. Configure dynamic trunking protocol to propagate VLAN information.

Key Takeaways

The question tests which STP mode and which VLAN tool each map to the three stated goals; the trap is picking MST, whose identical per-switch region configuration actually increases manual error risk.

This 300-420 Layer 2 design question pairs Rapid PVST+ with VTP pruning to cut topology-change impact and manual VLAN work. The correct choices are A and C.

Common mistake: Choosing B with C: MST scales well, but its region name, revision and instance mapping must be entered identically on every switch, which increases — rather than reduces — manual configuration errors in this scenario.

Expert Analysis

Trace the topology-change path first. The site runs legacy 802.1D, where a link failure forces every switch through listening/learning timers of roughly 30–50 seconds before forwarding resumes. Option A replaces that timer-driven process with Rapid PVST+, whose proposal/agreement handshake converges in sub-second time, directly shrinking both the duration and the blast radius of each topology change. That satisfies the first goal.

Trace the VLAN administration path next. Today every switch is configured by hand, so each new or renamed VLAN must be typed on every device — the exact source of the errors the architect wants to remove. Option C makes one VTP server authoritative: clients learn the VLAN database automatically, and VTP pruning removes unused VLANs from trunk allow-lists without touching each switch. Fewer per-switch touches means less administration time and fewer transcription mistakes, covering goals two and three.

Why option B loses the tie-break. MST does scale better than per-VLAN instances, but enabling it requires the region name, revision and instance-to-VLAN mapping to be configured identically on every switch in the region. That is more manual, error-prone work in a domain whose stated weakness is manual configuration, and a mismatch silently splits the region. Commenters who favour B also concede MST "require certain downtime" and must be "configured on every switch," which cuts against the second and third goals.

Why D and E fail outright. Option D's storm control mitigates broadcast/multicast flooding; it changes nothing about convergence time or configuration workload. Option E is factually wrong: DTP negotiates whether a link becomes a trunk, it does not propagate VLAN membership — only VTP does that.

Verdict: A and C. Rapid PVST+ (A) fixes the topology-change impact; VTP with pruning (C) fixes administration time and manual errors.

Official Reference

https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10556-16.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

When a question lists three goals and asks for two answers, label each option with the goal it satisfies before choosing. Here only option A touches convergence after a topology change, and only option C touches per-switch VLAN workload, so A+C covers all three goals with no gaps. Treat any option whose feature requires identical hand-typing on every switch (MST regions) as a mismatch for a 'reduce manual errors' goal, and verify each distractor's factual claim — DTP negotiates trunks, it does not propagate VLANs.

Frequently Asked Questions

Why isn't MST the better answer for reducing the impact of topology changes?

MST scales well, but enabling it requires the region name, revision and instance-to-VLAN mapping to be configured identically on every switch. In a domain whose stated problem is manual configuration errors, that extra per-switch work makes it a worse fit than Rapid PVST+.

Does VTP pruning actually reduce manual configuration errors?

Yes. A single VTP server holds the VLAN database, so clients learn VLANs automatically and pruning removes unused VLANs from trunk allow-lists without editing each switch, eliminating repeated manual VLAN entries.

Why is option E wrong about DTP?

Dynamic Trunking Protocol only negotiates whether a link becomes a trunk and in which mode; it never carries or propagates VLAN membership information. Only VTP distributes the VLAN database.

More 300-420 FAQ →

Community Votes

C
50%
A
32%
B
18%

50% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 19 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 19

  1. jddalo 👍 11
    I think its A & C
  2. XalaGyan 👍 4
    A customer's current Layer 2 infrastructure is running Spanning Tree 802.1d, and all configuration changes are manually implemented on each switch. An architect must redesign the Layer 2 domain to achieve these goals: reduce the impact of topology changes ==> MST reduce the time spent on network administration ==> VTP (with MST vtp3) * reduce manual configuration errors ==> VTP Pruning ??? Which two solutions should the architect include in the new design? (Choose two.) I strongly believe MST and VTP ( B and C) should be appropriate here. Please comment
  3. MangoBingsu 👍 4
    I believe its A &C as well
  4. andrewChan 👍 3
    B- implement MST require certain downtime if network contrains lots of switches D- not related to any requirement E- DTP is not propagate VLAN info, instead how the trunk link form so rest A, C A - RPVST and PVST (STP) can coexist C- setup VTP server (although answer does not mention but requrire when purning) and purning unused VLAN..... on the other hand, the biggest errors is removing VLAN(s) on the VTP server accidentally and propergate to whole switch network. So most of real implementation are using VTP mode transparent instead
  5. Clauster 👍 3
    Realistically speaking A and C are the best answers. MSTP requires you to configure each switch manually causing more administrative overhead. It's also fishy that the answer said "MST" instead of MSTP so that's another reason i am choosing A instead of B.
Show 14 more comments
  1. SpicyMochi 👍 2
    A. Implement Rapid PVST+ instead of STP. C. Use VTP to propagate VLAN information and to prune unused VLANs. To achieve the stated goals of reducing the impact of topology changes, reducing the time spent on network administration, and reducing manual configuration errors, the architect should implement the following solutions: A. Implement Rapid PVST+ (Per VLAN Spanning Tree Plus) instead of STP (Spanning Tree Protocol). Rapid PVST+ is based on the IEEE 802.1w standard (Rapid Spanning Tree Protocol) and converges faster than the traditional 802.1d STP. This will help to reduce the impact of topology changes. C. Use VTP (VLAN Trunking Protocol) to propagate VLAN information and to prune unused VLANs. VTP is a Cisco proprietary protocol that simplifies VLAN administration across multiple switches by automatically distributing VLAN configuration information. This reduces the time spent on network administration and the potential for manual configuration errors.
  2. python_tamer 👍 2
    For MST to work properly, the config has to be correctly configured on every switch in the L2 domain. I think this goes against the requirement for "reduce manual configuration errors", so I'm going with A and C.
  3. LSLS55 👍 2
    Lets not forget this is a Cisco exam and unless stated that another vendor is used or a specific protocol is not compatible, go with Cisco proprietary protocols. I would say it's A and C.
  4. cwoolie 👍 2
    A C is answer
  5. roganjosh 👍 2
    It's A and C
  6. G_Singh12 👍 1
    The customer is currently running standard 802.1D Spanning Tree Protocol (STP), which has a slow convergence time (30 to 50 seconds) during topology changes. Upgrading to Rapid Per-VLAN Spanning Tree Plus (Rapid PVST+) introduces sub-second convergence, dramatically minimizing network downtime when links fail or topology changes occur B is incorrect. Although While MST reduces the impact of topology changes, it introduces a high level of administrative complexity due to managing multiple regions, instances, and manual VLAN-to-instance mappings. This contradicts the goals of reducing administration time and manual errors.
  7. Clauster 👍 1
    Answers are B & C please hear me out so you don't get this wrong on the exam. - We need a Protocol that is best suited to reduce admin overhead (RSTP and MSTP are both suited) - We need a protocol that helps us reduce VLAN configuration, this is without a doubt VTP. - We need a protocol that reduces MANUAL CONFIGURATION, unfortunately RSTP does not meet this requirement because you have to configure everything manually on every switch in the network therefor leaving MSTP as the our only and final winner. Hope this helps you guys.
  8. Clauster 👍 1
    The correct answers are B & C Rapid PVST+ requires too much manual configuration on it's ports, one of the requirements is to reduce Administrator Overhead, you reduce Admin Overhead with MST, MSTP is the entire reason you can run it on Data Centers because of how many VLANs can be ran. VTP Allows VLAN to flow through out the Network again reducing Administrator Overhead. MSTP is also fast to converge. I hope this clears up your doubts.
  9. 19698e8 👍 1
    A. Implement Rapid PVST+ instead of STP This is the most tempting distractor. Rapid PVST+: ✅ Faster convergence than 802.1D. But: ❌ Still maintains one STP instance per VLAN. ❌ Does not reduce administration time. ❌ Does not reduce manual VLAN configuration errors. MST provides both scalability and reduced impact of topology changes, making it the better design answer.
  10. 26d13e9 👍 1
    B can not work with C. The basic idea of MSTP is to have all vlans configured on all interfaces. If this is the case, then you can not have something like VTP disturbing that system via going around and pruning vlans. If we are choosing C, then the other one may be A.
  11. DOSKIM 👍 1
    environement may include non cisco switch so in this case i will go wtih MST and VTP as PVST+ is cisco proprietary. MST is standard.
  12. Noproblem22 👍 1
    AC is the best answer. CD will not reduce the impact of topology change.
  13. cerifyme85 👍 1
    VTP server mode not recommeded
  14. zlimvos 👍 1
    Also think A and C

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