CCNP Network Function Virtualization Practice Question
This 350-401 practice question tests your understanding of network function virtualization. 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 company is migrating its legacy firewall services to a virtualized environment using Cisco NFV. The network engineer deploys a virtual firewall (vFW) on an NFVIS-enabled UCS platform. After the deployment, traffic through the vFW is intermittent and performance monitoring shows high CPU usage on the host. Which action should the engineer take to improve performance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable SR-IOV on the physical NICs and assign VFs to the vFW.
SR-IOV (Single Root I/O Virtualization) allows a physical NIC to present multiple virtual functions (VFs) directly to a VM, bypassing the hypervisor's virtual switch and reducing CPU overhead for packet processing. In an NFVIS environment, high host CPU usage with intermittent traffic indicates that the vFW is consuming excessive CPU cycles due to software-based I/O. Assigning VFs to the vFW offloads packet handling to the NIC hardware, lowering host CPU utilization and stabilizing traffic.
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.
✓
Enable SR-IOV on the physical NICs and assign VFs to the vFW.
Why this is correct
Correct because SR-IOV allows the vFW to directly access the physical NIC, reducing CPU overhead and improving throughput.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the number of vCPUs allocated to the vFW VM.
Why it's wrong here
Incorrect because more vCPUs do not solve the hypervisor switching bottleneck; SR-IOV is needed.
✗
Configure QoS policies on the vFW to prioritize traffic.
Why it's wrong here
Incorrect because QoS manages bandwidth allocation, not CPU utilization or packet processing efficiency.
✗
Disable hyperthreading on the host CPU.
Why it's wrong here
Incorrect because disabling hyperthreading typically reduces parallel processing capability, worsening performance.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume adding more vCPUs (Option B) will solve performance issues, but Cisco tests the understanding that I/O bottlenecks in NFV are typically resolved by hardware offload techniques like SR-IOV, not by increasing compute resources.
Detailed technical explanation
How to think about this question
SR-IOV works by partitioning a single physical PCIe device into multiple VFs, each with dedicated DMA and interrupt resources, enabling near-native I/O performance. In NFVIS, the vFW typically uses a virtio or e1000 driver without SR-IOV, causing all packet processing to traverse the hypervisor's vSwitch and consume host CPU cycles. A real-world scenario is a virtual firewall handling high-throughput traffic (e.g., 10 Gbps) where SR-IOV can reduce host CPU usage by over 50% compared to para-virtualized drivers.
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.
Network Function Virtualization — This question tests Network Function Virtualization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable SR-IOV on the physical NICs and assign VFs to the vFW. — SR-IOV (Single Root I/O Virtualization) allows a physical NIC to present multiple virtual functions (VFs) directly to a VM, bypassing the hypervisor's virtual switch and reducing CPU overhead for packet processing. In an NFVIS environment, high host CPU usage with intermittent traffic indicates that the vFW is consuming excessive CPU cycles due to software-based I/O. Assigning VFs to the vFW offloads packet handling to the NIC hardware, lowering host CPU utilization and stabilizing traffic.
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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