This 200-901 practice question tests your understanding of network fundamentals. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Exhibit
Refer to the exhibit.
```
interface GigabitEthernet0/1
switchport mode access
switchport access vlan 10
spanning-tree portfast
```
Refer to the exhibit. A PC is connected to interface GigabitEthernet0/1 on a Cisco switch. The PC is in VLAN 10. What is the purpose of the 'spanning-tree portfast' command on this interface?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
It allows the interface to transition directly to forwarding state.
PortFast brings the interface to forwarding state immediately, bypassing STP listening and learning states. This speeds up access port 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.
✗
It disables STP on the interface.
Why it's wrong here
STP still runs but portfast bypasses listening/learning.
✗
It prevents the interface from entering blocking state.
Why it's wrong here
PortFast allows immediate forwarding, but blocking is still possible if BPDUs are received.
✓
It allows the interface to transition directly to forwarding state.
Why this is correct
PortFast eliminates the learning/listening delays.
Related concept
Access ports place end devices into a single VLAN.
PortFast does not enable RSTP; it is a feature for access ports.
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.
What to study next
Got this wrong? Here's your next step.
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 200-901 questions on switching, trunking, and access-port configuration.
Network Fundamentals — This question tests Network Fundamentals — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: It allows the interface to transition directly to forwarding state. — PortFast brings the interface to forwarding state immediately, bypassing STP listening and learning states. This speeds up access port convergence.
What should I do if I get this 200-901 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 200-901 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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Question Discussion
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