The correct answer is that Spanning Tree PortFast allows the port to immediately transition to the forwarding state, bypassing the listening and learning phases. This configuration is applied to an access port connecting an end host, such as a PC or printer, where no switch or bridge is expected. By enabling PortFast, the switch eliminates the 30-second delay (15 seconds for listening, 15 for learning) that standard Spanning Tree Protocol would impose, thereby reducing STP convergence time for end hosts and preventing boot-time connectivity issues. On the ENCOR 350-401 exam, this concept tests your understanding of STP optimization features and their appropriate use cases; a common trap is applying PortFast to trunk ports or ports connecting to other switches, which can cause loops. Remember the memory tip: “PortFast for hosts, not for switches—skip the wait, forward straight.”
350-401 Cisco DNA Center Practice Question
This 350-401 practice question tests your understanding of cisco dna center. 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.
Examine the following partial Cisco IOS-XE configuration:
interface GigabitEthernet0/1
switchport mode access
switchport access vlan 10
ip access-group ACL_IN in
spanning-tree portfast
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, reducing STP convergence time for end hosts.
The configuration enables PortFast on an access port, allowing it to transition directly to forwarding state, bypassing the listening and learning phases. This is commonly used for end-host ports to avoid delays caused by spanning-tree convergence.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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, reducing STP convergence time for end hosts.
Why this is correct
spanning-tree portfast on an access port causes immediate forwarding, as intended for host ports.
Related concept
Access ports place end devices into a single VLAN.
✗
The port will become a trunk port and participate in VLAN trunking.
The port will use Rapid PVST+ and immediately forward after a link failure.
Why it's wrong here
PortFast does not change the STP mode; it only affects initial convergence.
✗
The port will block all inbound traffic due to the ACL.
Why it's wrong here
The ACL is applied inbound but does not block all traffic; it filters based on the ACL entries.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.
Cisco DNA Center — This question tests Cisco DNA Center — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The port will immediately transition to forwarding state, reducing STP convergence time for end hosts. — The configuration enables PortFast on an access port, allowing it to transition directly to forwarding state, bypassing the listening and learning phases. This is commonly used for end-host ports to avoid delays caused by spanning-tree convergence.
What should I do if I get this 350-401 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 350-401 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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