The answer is to configure both sides with switchport mode trunk. This resolves DTP trunk negotiation issues because when one switch is set to dynamic desirable and the other to trunk mode, DTP frames are still exchanged, but the static trunk side does not actively negotiate, leading to timing mismatches and intermittent connectivity. The dynamic desirable side expects DTP responses that the trunk mode side may not consistently provide, causing the link to flap or fail to establish a stable trunk. On the ENCOR 350-401 exam, this scenario tests your understanding of DTP behavior and the importance of disabling negotiation for reliability; a common trap is assuming dynamic desirable and trunk mode are fully compatible. Remember the memory tip: “Static trunk stops the DTP talk” — if you want a stable trunk, set both ends to switchport mode trunk to eliminate DTP negotiation entirely.
CCNP Network Assurance Practice Question
This 350-401 practice question tests your understanding of network assurance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
A network engineer notices intermittent connectivity issues between two switches connected via a trunk link. The trunk is configured with DTP in dynamic desirable mode on one side and trunk mode on the other. Which action should the engineer take to resolve the issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure both sides with switchport mode trunk.
The correct answer is A because Dynamic Trunking Protocol (DTP) in dynamic desirable mode actively attempts to negotiate a trunk, but when the other side is set to trunk mode (which is a static trunk configuration), DTP negotiation can still cause intermittent issues due to mismatched DTP frames or timing. Configuring both sides with switchport mode trunk disables DTP negotiation entirely, ensuring a stable, static trunk link without negotiation delays or failures.
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.
✓
Configure both sides with switchport mode trunk.
Why this is correct
Option A is correct because it ensures both ends are unconditionally set to trunk mode, avoiding negotiation issues.
Related concept
Read the scenario before looking for a memorised answer.
✗
Set both sides to access mode.
Why it's wrong here
Option D is wrong because access mode would not carry multiple VLANs, breaking the trunk.
✗
Disable DTP on both sides using switchport nonegotiate.
Why it's wrong here
Option B is wrong because disabling DTP may prevent the trunk from forming if the other side is not statically configured.
✗
Change one side to dynamic auto.
Why it's wrong here
Option C is wrong because dynamic auto waits for the other side to initiate trunking, which may not happen.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that dynamic desirable and trunk mode are compatible because both result in a trunk, but the trap is that DTP negotiation can cause instability, and the correct solution is to use static trunk configuration on both sides to avoid reliance on DTP.
Detailed technical explanation
How to think about this question
DTP operates at Layer 2 and uses Cisco proprietary frames to negotiate trunking between switches; dynamic desirable sends DTP frames to actively form a trunk, while trunk mode is a static configuration that also sends DTP frames by default. The intermittent issue arises because DTP negotiation can fail or flap if there is a delay in frame exchange or a mismatch in the DTP state machine, especially in environments with high CPU load or link flaps. In real-world scenarios, best practice is to use switchport mode trunk with switchport nonegotiate on both ends to eliminate DTP overhead and ensure deterministic trunk behavior.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Assurance — This question tests Network Assurance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure both sides with switchport mode trunk. — The correct answer is A because Dynamic Trunking Protocol (DTP) in dynamic desirable mode actively attempts to negotiate a trunk, but when the other side is set to trunk mode (which is a static trunk configuration), DTP negotiation can still cause intermittent issues due to mismatched DTP frames or timing. Configuring both sides with switchport mode trunk disables DTP negotiation entirely, ensuring a stable, static trunk link without negotiation delays or failures.
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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