- A
Pin the vCPU of the CSR1000v to dedicated physical cores and ensure the VM memory is allocated from the same NUMA node.
CPU pinning and NUMA locality reduce latency and improve performance by avoiding cross-NUMA memory access.
- B
Use a Type 2 hypervisor to allow the VNF to share resources with other VMs more efficiently.
Why wrong: Type 2 hypervisors add overhead; Type 1 (bare-metal) is preferred for performance-sensitive VNFs.
- C
Enable overcommitment of CPU resources to maximize the number of VNFs per host.
Why wrong: Overcommitment can cause CPU contention, increasing latency and reducing throughput for the CSR1000v.
- D
Place the CSR1000v on a VMware ESXi host instead of KVM for better performance.
Why wrong: Both hypervisors can perform well with proper tuning; the key is CPU pinning and NUMA awareness, not the hypervisor brand.
Quick Answer
The answer is pinning the vCPU of the CSR1000v to dedicated physical cores and ensuring the VM memory is allocated from the same NUMA node. This is the most critical architectural consideration for NFV performance optimization because it eliminates cross-NUMA memory access and CPU scheduling contention, which are the primary sources of latency in data-plane-intensive virtual routers. Without vCPU pinning, the hypervisor may migrate the vCPU across cores, breaking CPU cache locality; without NUMA locality, memory accesses must traverse the slower QPI/UPI interconnect, severely degrading throughput. On the ENCOR 350-401 exam, this concept tests your understanding of how to optimize virtualized network functions (VNFs) for high-throughput, low-latency traffic, often appearing in scenario-based questions where a trap answer suggests over-provisioning CPU cores or relying on balloon drivers. A common memory tip is “pin and stay local”—if the vCPU and its memory aren’t on the same NUMA node, the virtual router will suffer a “remote memory penalty” that no amount of CPU speed can fix.
CCNP QoS Architecture Practice Question
This 350-401 practice question tests your understanding of qos 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 company is virtualizing its network functions using NFV on a KVM-based hypervisor. The design must ensure that the virtual router (CSR1000v) can handle high-throughput traffic with minimal latency. Which architectural consideration is most critical for achieving this goal?
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
Pin the vCPU of the CSR1000v to dedicated physical cores and ensure the VM memory is allocated from the same NUMA node.
Pinning vCPUs to dedicated physical cores and allocating memory from the same NUMA node eliminates cross-NUMA memory access and CPU scheduling contention, which are critical for reducing latency and maximizing throughput in a data-plane-intensive VNF like the CSR1000v. This ensures that the VM's memory accesses are local to the NUMA node where its vCPUs run, avoiding the performance penalty of remote memory access over the QPI/UPI interconnect.
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.
- ✓
Pin the vCPU of the CSR1000v to dedicated physical cores and ensure the VM memory is allocated from the same NUMA node.
Why this is correct
CPU pinning and NUMA locality reduce latency and improve performance by avoiding cross-NUMA memory access.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a Type 2 hypervisor to allow the VNF to share resources with other VMs more efficiently.
Why it's wrong here
Type 2 hypervisors add overhead; Type 1 (bare-metal) is preferred for performance-sensitive VNFs.
- ✗
Enable overcommitment of CPU resources to maximize the number of VNFs per host.
Why it's wrong here
Overcommitment can cause CPU contention, increasing latency and reducing throughput for the CSR1000v.
- ✗
Place the CSR1000v on a VMware ESXi host instead of KVM for better performance.
Why it's wrong here
Both hypervisors can perform well with proper tuning; the key is CPU pinning and NUMA awareness, not the hypervisor brand.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that simply using a Type 1 hypervisor or avoiding overcommitment is sufficient, but the trap here is that candidates overlook the critical impact of NUMA locality and vCPU pinning on latency-sensitive VNFs, assuming that any virtualization optimization will suffice.
Detailed technical explanation
How to think about this question
NUMA (Non-Uniform Memory Access) architecture means that memory access time depends on the memory location relative to the processor. When a VM's vCPUs and memory are not on the same NUMA node, every memory access must traverse the inter-socket interconnect (e.g., Intel QPI or UPI), adding significant latency—often 1.5x to 2x slower. In a real-world scenario, a CSR1000v handling BGP updates and forwarding packets at line rate would suffer packet drops and jitter if its memory is remote, making vCPU pinning and NUMA-aware memory allocation a mandatory best practice for NFV performance.
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
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FAQ
Questions learners often ask
What does this 350-401 question test?
QoS Architecture — This question tests QoS Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Pin the vCPU of the CSR1000v to dedicated physical cores and ensure the VM memory is allocated from the same NUMA node. — Pinning vCPUs to dedicated physical cores and allocating memory from the same NUMA node eliminates cross-NUMA memory access and CPU scheduling contention, which are critical for reducing latency and maximizing throughput in a data-plane-intensive VNF like the CSR1000v. This ensures that the VM's memory accesses are local to the NUMA node where its vCPUs run, avoiding the performance penalty of remote memory access over the QPI/UPI interconnect.
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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