The answer is to ensure all VNFs are pinned to the same NUMA node on the hypervisor host. This design consideration is critical for low latency NFV because it eliminates the need for memory accesses to traverse the QPI or UPI interconnect between separate NUMA nodes, which introduces significant delay. In a virtualized service chain, co-locating the firewall, WAN optimizer, and IPS on the same NUMA node keeps all packet processing within a single memory domain, minimizing latency for real-time traffic. On the ENCOR 350-401 exam, this concept tests your understanding of how hypervisor resource allocation directly impacts NFV performance; a common trap is assuming any single host placement is sufficient, ignoring the NUMA topology. Remember the memory tip: “Same node, same speed—cross the QPI, and your packets bleed.”
350-401 Virtual Machines and Hypervisors Practice Question
This 350-401 practice question tests your understanding of virtual machines and hypervisors. 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.
An architect is designing a virtualized service chain for a campus network using NFV. The chain must include a firewall, WAN optimizer, and IPS. The architect needs to minimize latency by placing VNFs on the same hypervisor host. Which design consideration is most important?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Ensure all VNFs are pinned to the same NUMA node on the hypervisor host.
Option A is correct because pinning all VNFs to the same NUMA node on the hypervisor host minimizes inter-NUMA memory access latency, which is critical for achieving low-latency packet processing in an NFV service chain. When VNFs are placed on different NUMA nodes, memory accesses must traverse the QPI/UPI interconnect, adding significant latency. By co-locating the firewall, WAN optimizer, and IPS on the same NUMA node, the architect ensures that all packet processing stays within the same memory domain, reducing latency to the minimum possible on that host.
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.
✓
Ensure all VNFs are pinned to the same NUMA node on the hypervisor host.
Why this is correct
This minimizes memory access latency and improves performance for the service chain.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a Type 2 hypervisor to reduce overhead.
Why it's wrong here
Type 2 hypervisors add more overhead and are not suitable for production NFV.
✗
Place each VNF on a separate physical host to avoid resource contention.
Why it's wrong here
This increases latency due to network hops between hosts.
✗
Enable DPDK on the virtual switch to accelerate packet processing.
Why it's wrong here
DPDK helps performance but does not directly address NUMA locality.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that DPDK or a Type 2 hypervisor is the primary solution for low-latency NFV, when in fact NUMA awareness is the foundational requirement that must be addressed first.
Detailed technical explanation
How to think about this question
NUMA (Non-Uniform Memory Access) architecture divides a physical host into multiple nodes, each with its own memory controller and CPU cores. When a VNF on one NUMA node accesses memory allocated on another node, the latency penalty is typically 1.5–2x higher due to the QPI/UPI hop. In a service chain, each packet traverses multiple VNFs, so even a small per-hop latency increase compounds dramatically. Real-world NFV deployments use CPU pinning and memory affinity (e.g., via libvirt's `numatune` or VMware's NUMA affinity) to ensure all VNFs in a chain share the same NUMA node, often combined with huge pages to further reduce TLB misses.
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.
Virtual Machines and Hypervisors — This question tests Virtual Machines and Hypervisors — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Ensure all VNFs are pinned to the same NUMA node on the hypervisor host. — Option A is correct because pinning all VNFs to the same NUMA node on the hypervisor host minimizes inter-NUMA memory access latency, which is critical for achieving low-latency packet processing in an NFV service chain. When VNFs are placed on different NUMA nodes, memory accesses must traverse the QPI/UPI interconnect, adding significant latency. By co-locating the firewall, WAN optimizer, and IPS on the same NUMA node, the architect ensures that all packet processing stays within the same memory domain, reducing latency to the minimum possible on that host.
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.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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