The correct approach is to set the trust boundary at the access layer switch and re-mark packets based on source. This placement is critical because the access layer is the closest trusted point to the endpoint, allowing the network to enforce policy before traffic enters the distribution or core layers. By re-marking packets based on source—for example, trusting only IP phones while re-marking all workstation traffic to a default or lower priority—you prevent unauthorized or misconfigured endpoints from injecting false QoS markings that could degrade voice or video quality. On the ENCOR 350-401 exam, this concept tests your understanding of where to establish trust in a converged network; a common trap is placing the trust boundary at the distribution layer, which is too far from the source and allows untrusted traffic to influence core QoS. Remember the memory tip: “Trust at the edge, mark at the source”—the access layer switch is your first line of defense for QoS policy enforcement.
350-401 Architecture Practice Question
This 350-401 practice question tests your understanding of 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.
A network administrator is deploying QoS in a converged network. Which approach correctly implements trust boundaries and marking?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set trust boundary at the access layer switch and re-mark packets based on source.
Option A is correct because in a converged network, trust boundaries should be established at the access layer to ensure that marking decisions are made as close to the source as possible. By setting the trust boundary at the access layer switch and re-marking packets based on source (e.g., trusting only IP phones while re-marking workstation traffic), the network can enforce policy before traffic enters the core, preventing unauthorized or misconfigured endpoints from influencing QoS markings. This aligns with Cisco's best practice of trusting only known devices and re-marking all other traffic to a default or lower priority.
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.
✓
Set trust boundary at the access layer switch and re-mark packets based on source.
Why this is correct
The access layer is the ideal trust boundary to enforce QoS policies.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure marking only at the core layer to simplify policy.
Why it's wrong here
Marking at the core is ineffective for upstream prioritization.
✗
Trust only the distribution layer switches to mark traffic.
Why it's wrong here
Traffic reaches the distribution layer already, so marking there is too late for proper queuing.
✗
Trust the DSCP values set by IP phones and workstations.
Why it's wrong here
End devices may not be trustworthy; marking should be done at the access switch.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that trust boundaries should be placed at the distribution or core layer for simplicity, but the trap is that marking must happen at the access layer to prevent untrusted endpoints from injecting high-priority traffic into the network.
Detailed technical explanation
How to think about this question
Under the hood, the trust boundary is enforced using the 'mls qos trust' interface command on Cisco switches, which can be set to 'cos', 'dscp', or 'ip-precedence', and combined with 'mls qos trust device cisco-phone' to automatically trust the phone's markings while re-marking traffic from the attached PC. In a real-world scenario, failing to properly configure trust boundaries can allow a rogue workstation to set DSCP EF (46), causing voice queues to be flooded with data traffic and degrading call quality. The access layer switch uses a configurable CoS-to-DSCP or DSCP-to-DSCP mutation map to re-mark untrusted traffic to a lower priority, such as DSCP 0 (best effort).
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 practitioner preparing for the 350-401 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set trust boundary at the access layer switch and re-mark packets based on source. — Option A is correct because in a converged network, trust boundaries should be established at the access layer to ensure that marking decisions are made as close to the source as possible. By setting the trust boundary at the access layer switch and re-marking packets based on source (e.g., trusting only IP phones while re-marking workstation traffic), the network can enforce policy before traffic enters the core, preventing unauthorized or misconfigured endpoints from influencing QoS markings. This aligns with Cisco's best practice of trusting only known devices and re-marking all other traffic to a default or lower priority.
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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