- A
Place all VNFs for a customer on a single hypervisor host and use internal virtual switches to chain them.
Why wrong: While this reduces inter-VNF latency, it does not scale well across many customers and creates a single point of failure.
- B
Use a centralized service chain with a service graph that defines the order of VNFs, and deploy VNFs on separate hosts for redundancy.
This model uses a service graph to define the chain, and VNFs can be placed on separate hosts for high availability, allowing per-customer customization and scaling.
- C
Deploy each VNF as a separate virtual machine on a dedicated physical server to maximize performance.
Why wrong: Dedicated servers per VNF are costly and do not leverage the benefits of virtualization and service chaining.
- D
Use a single VNF that combines routing and firewall functions to avoid chaining complexity.
Why wrong: Combining functions into a single VNF reduces flexibility and may not meet all customer requirements for separate security and routing policies.
Quick Answer
The correct answer is the centralized service chain with a service graph, because this model defines the ordered sequence of VNFs—such as a vEdge router followed by a firewall—and allows deployment on separate hosts for redundancy, directly aligning with NFV MANO principles for efficient per-customer scaling. In the ENCOR 350-401 exam, this tests your understanding of how service graphs abstract the VNF placement model within an SD-WAN VNF placement scenario, ensuring you can distinguish it from simpler models like a flat chain or all-in-one host. A common trap is assuming VNFs must share a single hypervisor for performance, but the exam emphasizes that separate hosts provide fault isolation while the service graph maintains logical ordering. Memory tip: think of the service graph as a “recipe card” that lists the steps (VNFs) and the hosts as separate ovens—each customer gets their own batch without burning the whole kitchen.
CCNP SD-WAN Architecture Practice Question
This 350-401 practice question tests your understanding of sd-wan architecture. 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.
A service provider is deploying NFV to offer managed SD-WAN services to enterprise customers. The architect must place virtual network functions (VNFs) such as vEdge routers and firewalls in the provider's data center. Which VNF placement model allows the provider to chain these functions efficiently and scale per customer?
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
Use a centralized service chain with a service graph that defines the order of VNFs, and deploy VNFs on separate hosts for redundancy.
Option B is correct because a centralized service chain with a service graph allows the provider to define the ordered sequence of VNFs (e.g., vEdge router then firewall) and deploy them on separate hosts for redundancy. This model aligns with NFV MANO (Management and Orchestration) principles, enabling efficient scaling per customer by instantiating VNFs as needed while maintaining the service chain across hypervisors.
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.
- ✗
Place all VNFs for a customer on a single hypervisor host and use internal virtual switches to chain them.
Why it's wrong here
While this reduces inter-VNF latency, it does not scale well across many customers and creates a single point of failure.
- ✓
Use a centralized service chain with a service graph that defines the order of VNFs, and deploy VNFs on separate hosts for redundancy.
Why this is correct
This model uses a service graph to define the chain, and VNFs can be placed on separate hosts for high availability, allowing per-customer customization and scaling.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Deploy each VNF as a separate virtual machine on a dedicated physical server to maximize performance.
Why it's wrong here
Dedicated servers per VNF are costly and do not leverage the benefits of virtualization and service chaining.
- ✗
Use a single VNF that combines routing and firewall functions to avoid chaining complexity.
Why it's wrong here
Combining functions into a single VNF reduces flexibility and may not meet all customer requirements for separate security and routing policies.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that placing all VNFs on a single host (Option A) is simpler and efficient, but the trap is that this violates NFV's high-availability and multi-tenant scaling requirements, which are core to service provider SD-WAN offerings.
Detailed technical explanation
How to think about this question
In NFV, service graphs are defined using YANG models (e.g., IETF RFC 8453) and orchestrated by the NFV Orchestrator (NFVO) to chain VNFs via virtual links. For SD-WAN, vEdge routers often use OMP (Overlay Management Protocol) for control plane, while firewalls enforce policies; chaining them in a service graph ensures traffic flows through the correct sequence without manual VLAN stitching. Real-world deployments use VNF forwarding graphs (VNFFG) to automate this, allowing per-customer scaling by spinning up VNF instances on different hosts while maintaining the chain via overlay tunnels.
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.
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.
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FAQ
Questions learners often ask
What does this 350-401 question test?
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: Use a centralized service chain with a service graph that defines the order of VNFs, and deploy VNFs on separate hosts for redundancy. — Option B is correct because a centralized service chain with a service graph allows the provider to define the ordered sequence of VNFs (e.g., vEdge router then firewall) and deploy them on separate hosts for redundancy. This model aligns with NFV MANO (Management and Orchestration) principles, enabling efficient scaling per customer by instantiating VNFs as needed while maintaining the service chain across hypervisors.
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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Last reviewed: Jun 24, 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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