The answer is that the control policy is not attached to the appropriate site list or VPN list. In Cisco SD-WAN, a centralized control policy configured on the vSmart controller only takes effect when it is explicitly associated with a site list or VPN list, which defines the specific vEdge routers or traffic flows the policy should influence. Without this attachment, the vSmart will not push the policy to the targeted branches, leaving them to rely on the default OMP best-path selection based on administrative distance and cost, even though connectivity to the vSmart is intact. On the ENCOR 350-401 exam, this scenario tests your understanding of how policy scoping works in SD-WAN, often appearing as a trap where candidates assume reachability alone ensures policy application. A common memory tip is to think of the site list as the “address” for the policy—without it, the policy has no destination and stays on the vSmart.
350-401 SD-WAN Architecture Practice Question
This 350-401 practice question tests your understanding of sd-wan architecture. 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.
An enterprise is migrating from a traditional MPLS WAN to Cisco SD-WAN. The network team has deployed vEdge routers at all branch offices and a vSmart controller in the data center. The engineer configures a centralized control policy to influence path selection based on cost and latency. After the policy is activated, the engineer notices that some branches are not receiving the updated policy and are still using the default best-path selection. The vSmart is reachable from all branches, and the vEdge routers show that they are connected to the vSmart. What is the most likely reason for this issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The control policy is not attached to the appropriate site list or VPN list.
In Cisco SD-WAN, centralized control policies must be explicitly attached to a site list or VPN list to define which devices or traffic the policy applies to. If the policy is not attached to the appropriate list, the vSmart controller will not push the policy to the targeted vEdge routers, causing them to continue using the default OMP best-path selection (based on administrative distance and cost). The fact that the vEdge routers are connected to the vSmart confirms the issue is with policy application, not reachability.
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.
✗
The vEdge routers have not been rebooted after the policy change.
Why it's wrong here
Incorrect because policy changes take effect immediately without reboot.
✓
The control policy is not attached to the appropriate site list or VPN list.
Why this is correct
Correct because a control policy must be associated with a list to be applied; otherwise, it is not enforced.
Clue confirmation
The clue words "best", "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The OMP graceful restart timer has expired, causing the vEdge to ignore the policy.
Why it's wrong here
Incorrect because OMP graceful restart affects route convergence, not policy application.
✗
The BFD sessions between vEdge and vSmart are flapping.
Why it's wrong here
Incorrect because BFD is for data plane failure detection, not for policy distribution.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the concept that a control policy must be attached to a site list or VPN list to be effective, and candidates mistakenly assume that simply configuring the policy on the vSmart is sufficient for it to apply to all devices.
Detailed technical explanation
How to think about this question
Centralized control policies in SD-WAN are configured on the vSmart and use match conditions (e.g., site-list, vpn-list) to filter routes and influence path selection. The policy is pushed to vEdge routers via OMP updates, and if the site list or VPN list does not include the branch's site ID or VPN, the policy is not applied. A common real-world mistake is forgetting to create or reference the site list, especially when branches are added after the initial policy deployment.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
SD-WAN Architecture — This question tests SD-WAN Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The control policy is not attached to the appropriate site list or VPN list. — In Cisco SD-WAN, centralized control policies must be explicitly attached to a site list or VPN list to define which devices or traffic the policy applies to. If the policy is not attached to the appropriate list, the vSmart controller will not push the policy to the targeted vEdge routers, causing them to continue using the default OMP best-path selection (based on administrative distance and cost). The fact that the vEdge routers are connected to the vSmart confirms the issue is with policy application, not reachability.
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.
Are there clue words in this question I should notice?
Yes — watch for: "best", "most likely". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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