The correct answer is that the port will immediately transition to a forwarding state and will be error-disabled if a BPDU is received. This occurs because the configuration combines PortFast, which bypasses the STP listening and learning phases to bring an access port directly into forwarding, with BPDU Guard, which actively monitors for incoming Bridge Protocol Data Units. If an unauthorized switch is connected and sends a BPDU, BPDU Guard error-disables the interface, preventing potential bridging loops and protecting the network from rogue devices. On the ENCOR 350-401 exam, this tests your understanding of STP edge port behavior and loop prevention mechanisms; a common trap is assuming PortFast alone provides security, when in fact BPDU Guard is required to enforce the access port boundary. Remember the mnemonic: "Fast to forward, Guard to guard—BPDU hits, port is marred."
350-401 SD-Access Architecture Practice Question
This 350-401 practice question tests your understanding of sd-access architecture. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The port will immediately transition to forwarding state and will be error-disabled if a BPDU is received.
The configuration enables PortFast and BPDU Guard on an access port. PortFast immediately transitions the port to forwarding state, bypassing the usual STP listening and learning phases. BPDU Guard monitors for incoming BPDUs; if any are received, it error-disables the port to prevent a potential bridging loop from an unauthorized switch connection.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The port will immediately transition to forwarding state and will be error-disabled if a BPDU is received.
Why this is correct
PortFast skips listening/learning; BPDU Guard error-disables the port on BPDU reception.
Related concept
Read the scenario before looking for a memorised answer.
✗
The port will remain in blocking state until a BPDU is received from the root bridge.
Why it's wrong here
PortFast overrides the normal STP state machine; the port goes directly to forwarding.
✗
The port will only forward BPDUs and will not forward data traffic.
Why it's wrong here
PortFast allows data traffic; BPDU Guard disables the port on BPDU reception, not just forward them.
✗
The port will participate in RSTP and will not be affected by BPDU reception.
Why it's wrong here
BPDU Guard is active and will error-disable the port upon BPDU reception, regardless of STP variant.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between PortFast (which speeds up convergence) and BPDU Guard (which protects against loops) — the trap here is assuming PortFast alone prevents BPDU issues, when in fact BPDU Guard is required to error-disable the port upon BPDU reception.
Detailed technical explanation
How to think about this question
PortFast sets the port to an STP edge port state, which skips the listening and learning phases and moves directly to forwarding. BPDU Guard, when enabled with 'spanning-tree bpduguard enable', places the port into errdisable state upon BPDU reception, which can be recovered manually or via errdisable recovery. In a real-world scenario, this is commonly used on switch ports connecting to end devices like PCs or printers to speed up convergence and protect against accidental loops from misconfigured devices.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
SD-Access Architecture — This question tests SD-Access Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The port will immediately transition to forwarding state and will be error-disabled if a BPDU is received. — The configuration enables PortFast and BPDU Guard on an access port. PortFast immediately transitions the port to forwarding state, bypassing the usual STP listening and learning phases. BPDU Guard monitors for incoming BPDUs; if any are received, it error-disables the port to prevent a potential bridging loop from an unauthorized switch connection.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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