- A
DTP is a Cisco proprietary protocol.
DTP is indeed Cisco proprietary and is not standardized in IEEE 802.1Q.
- B
The default switchport mode on a Cisco Catalyst switch is dynamic desirable.
By default, Cisco Catalyst switches use dynamic desirable mode, which actively sends DTP frames to negotiate trunking.
- C
DTP frames are sent continuously on a trunk port to maintain the trunk.
Why wrong: DTP frames are sent only during negotiation; once a trunk is established, DTP frames are no longer sent.
- D
The 'switchport nonegotiate' command enables DTP on an interface.
Why wrong: The 'switchport nonegotiate' command disables DTP, preventing the interface from sending DTP frames.
- E
DTP supports both 802.1Q and ISL trunking encapsulation.
Why wrong: DTP can negotiate both 802.1Q and ISL, but ISL is obsolete and not supported on modern switches; the statement is technically true but misleading in modern contexts, and the question focuses on current implementations where ISL is deprecated.
CCNP VLANs and Trunking Practice Question
This 350-401 practice question tests your understanding of vlans and trunking. 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.
Which two statements about DTP (Dynamic Trunking Protocol) are true? (Choose two.)
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
DTP is a Cisco proprietary protocol.
DTP is a Cisco proprietary protocol used to negotiate trunking between switches. The default mode on Cisco switches is dynamic desirable, which will actively try to form a trunk. DTP frames are sent only over access ports when trunking is being negotiated, but not over trunk ports once the trunk is established. The 'switchport nonegotiate' command disables DTP, and trunk formation then relies on manual configuration.
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.
- ✓
DTP is a Cisco proprietary protocol.
- ✓
The default switchport mode on a Cisco Catalyst switch is dynamic desirable.
- ✗
DTP frames are sent continuously on a trunk port to maintain the trunk.
- ✗
The 'switchport nonegotiate' command enables DTP on an interface.
Why it's wrong here
The 'switchport nonegotiate' command disables DTP, preventing the interface from sending DTP frames.
- ✗
DTP supports both 802.1Q and ISL trunking encapsulation.
Why it's wrong here
DTP can negotiate both 802.1Q and ISL, but ISL is obsolete and not supported on modern switches; the statement is technically true but misleading in modern contexts, and the question focuses on current implementations where ISL is deprecated.
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.
Trap categories for this question
Command / output trap
The 'switchport nonegotiate' command disables DTP, preventing the interface from sending DTP frames.
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 350-401 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 350-401 question test?
VLANs and Trunking — This question tests VLANs and Trunking — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: DTP is a Cisco proprietary protocol. — DTP is a Cisco proprietary protocol used to negotiate trunking between switches. The default mode on Cisco switches is dynamic desirable, which will actively try to form a trunk. DTP frames are sent only over access ports when trunking is being negotiated, but not over trunk ports once the trunk is established. The 'switchport nonegotiate' command disables DTP, and trunk formation then relies on manual configuration.
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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Last reviewed: Jun 18, 2026
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.
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