350-401 Network Function Virtualization Practice Question
This 350-401 practice question tests your understanding of network function virtualization. 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.
An enterprise is deploying a virtual router (vRouter) as part of its NFV infrastructure. The engineer needs to ensure that the vRouter can handle a sudden spike in traffic without dropping packets. The vRouter is running on a KVM hypervisor. What should the engineer configure to guarantee CPU resources for the vRouter during peak demand?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure CPU pinning and CPU reservation for the vRouter VM.
CPU pinning binds the vRouter's virtual CPUs to specific physical cores, preventing other processes from using them, while CPU reservation guarantees a minimum amount of CPU capacity. Together, they ensure deterministic CPU availability during traffic spikes, preventing packet drops due to resource contention on the KVM hypervisor.
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 memory ballooning on the vRouter VM.
Why it's wrong here
Incorrect because memory ballooning adjusts memory allocation, not CPU resources.
✓
Configure CPU pinning and CPU reservation for the vRouter VM.
Why this is correct
Correct because CPU pinning dedicates specific cores to the VM and reservation guarantees minimum CPU, preventing contention.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable DPDK on the vRouter's virtual NICs.
Why it's wrong here
Incorrect because DPDK accelerates packet processing but does not reserve CPU resources.
✗
Set the vRouter VM to use NUMA node pinning.
Why it's wrong here
Incorrect because NUMA pinning improves memory locality, not CPU availability.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between resource optimization (DPDK, NUMA) and resource guarantee (pinning, reservation), leading candidates to pick DPDK because it is associated with high performance, even though it does not guarantee CPU availability under contention.
Detailed technical explanation
How to think about this question
CPU pinning uses the `taskset` or `virsh vcpupin` commands to map vCPUs to specific pCPUs, while CPU reservation is set via the `<vcpu placement='static'>` and `<cpu><topology>` elements in the libvirt XML, or through OpenStack flavor extra specs like `hw:cpu_policy=dedicated`. In production NFV deployments, combining pinning with CPU reservation and isolating pCPUs using `isolcpus` kernel parameter prevents CPU steal time, which is critical for meeting strict latency and throughput SLAs for virtual routers.
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.
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: Configure CPU pinning and CPU reservation for the vRouter VM. — CPU pinning binds the vRouter's virtual CPUs to specific physical cores, preventing other processes from using them, while CPU reservation guarantees a minimum amount of CPU capacity. Together, they ensure deterministic CPU availability during traffic spikes, preventing packet drops due to resource contention on the KVM hypervisor.
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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