- A
Enable CPU overcommitment to allow the VNF to use any available CPU cycles.
Why wrong: CPU overcommitment can lead to performance variability and is not suitable for high-throughput VNFs.
- B
Configure NUMA pinning and CPU pinning to dedicate physical cores to the VNF's virtual CPUs.
NUMA pinning ensures memory locality and CPU pinning dedicates cores, providing consistent performance for the VNF.
- C
Use VMware vSphere instead of KVM for better VNF performance.
Why wrong: The question specifies KVM, and both hypervisors support CPU pinning; the answer must be specific to KVM.
- D
Increase the number of virtual CPUs assigned to the VNF to improve throughput.
Why wrong: Simply adding vCPUs without pinning can cause CPU scheduling contention and may not improve throughput.
Quick Answer
The correct answer is to configure NUMA pinning and CPU pinning to dedicate physical cores to the VNF’s virtual CPUs. CPU pinning binds each vCPU to a specific physical core, eliminating context-switching overhead and guaranteeing deterministic processing, while NUMA pinning ensures that the vCPUs and their associated memory reside on the same NUMA node, drastically reducing memory access latency. On the ENCOR 350-401 exam, this scenario tests your understanding of hypervisor performance tuning for VNFs, often appearing in questions about high-throughput virtualized network functions like next-generation firewalls. A common trap is to suggest overcommitting vCPUs or relying on default scheduling, which introduces jitter and bottlenecks. Remember the key principle: for VNF performance, you want zero CPU contention and local memory access. A helpful mnemonic is “Pin the CPU, match the NUMA node” — if you pin without aligning NUMA, you still risk cross-node memory penalties.
350-401 SD-WAN Architecture Practice Question
This 350-401 practice question tests your understanding of sd-wan 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.
An enterprise is deploying a virtualized network function (VNF) for a next-generation firewall on a KVM-based hypervisor. The architect must ensure that the VNF can handle high throughput without CPU bottlenecks. Which hypervisor configuration technique should the architect use to dedicate physical CPU cores to the VNF?
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
Configure NUMA pinning and CPU pinning to dedicate physical cores to the VNF's virtual CPUs.
Option B is correct because CPU pinning (also called CPU affinity) binds specific virtual CPUs (vCPUs) of the VNF to dedicated physical CPU cores, eliminating context-switching overhead and ensuring deterministic performance. NUMA pinning further aligns vCPUs and memory with the same Non-Uniform Memory Access node, reducing latency. This configuration is critical for VNFs like next-generation firewalls that require high throughput and low jitter.
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 CPU overcommitment to allow the VNF to use any available CPU cycles.
Why it's wrong here
CPU overcommitment can lead to performance variability and is not suitable for high-throughput VNFs.
- ✓
Configure NUMA pinning and CPU pinning to dedicate physical cores to the VNF's virtual CPUs.
Why this is correct
NUMA pinning ensures memory locality and CPU pinning dedicates cores, providing consistent performance for the VNF.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use VMware vSphere instead of KVM for better VNF performance.
Why it's wrong here
The question specifies KVM, and both hypervisors support CPU pinning; the answer must be specific to KVM.
- ✗
Increase the number of virtual CPUs assigned to the VNF to improve throughput.
Why it's wrong here
Simply adding vCPUs without pinning can cause CPU scheduling contention and may not improve throughput.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that simply increasing vCPU count (Option D) or enabling overcommitment (Option A) can solve performance issues, when in reality, dedicated core assignment via pinning is required for deterministic VNF throughput.
Detailed technical explanation
How to think about this question
Under the hood, CPU pinning uses the `taskset` or `virsh vcpupin` commands to set CPU affinity masks, ensuring that vCPUs run only on specified physical cores. NUMA pinning additionally requires mapping vCPUs and memory to the same NUMA node (e.g., via `numatune` in libvirt) to avoid cross-node memory access penalties, which can add 20-30% latency. In real-world deployments, a VNF performing stateful firewall inspection benefits from dedicated L1/L2 cache and reduced TLB misses, which are only achievable with strict pinning.
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.
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: Configure NUMA pinning and CPU pinning to dedicate physical cores to the VNF's virtual CPUs. — Option B is correct because CPU pinning (also called CPU affinity) binds specific virtual CPUs (vCPUs) of the VNF to dedicated physical CPU cores, eliminating context-switching overhead and ensuring deterministic performance. NUMA pinning further aligns vCPUs and memory with the same Non-Uniform Memory Access node, reducing latency. This configuration is critical for VNFs like next-generation firewalls that require high throughput and low jitter.
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.
About these practice questions
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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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