The correct choice is to assign the VM a virtual function (VF) using SR-IOV on the physical NIC. SR-IOV, or Single Root I/O Virtualization, enables a physical NIC to present multiple VFs directly to a VM, bypassing the hypervisor’s virtual switch and its associated CPU overhead. This direct hardware access for data plane traffic drastically reduces latency and processing delays, allowing the VM to achieve near line-rate throughput on a 10 Gbps link—critical for a virtualized WAN optimization appliance. On the ENCOR 350-401 exam, this question tests your understanding of virtualization performance optimization, often contrasting SR-IOV with paravirtualized drivers or emulated NICs. A common trap is choosing a dedicated physical NIC without SR-IOV, which wastes resources, or assuming a faster virtual switch alone solves the bottleneck. Remember: SR-IOV gives the VM a “fast lane” straight to the NIC hardware. Memory tip: “SR-IOV = Skip the vSwitch, Own the VF.”
CCNP 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.
A network team is deploying a virtualized WAN optimization appliance. The appliance must be able to process traffic at line rate on a 10 Gbps link. The hypervisor host has multiple physical NICs. Which design choice will best ensure the VM can achieve the required throughput?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Assign the VM a virtual function (VF) using SR-IOV on the physical NIC.
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. This reduces CPU overhead and latency, enabling the VM to achieve near line-rate throughput on a 10 Gbps link by allowing direct hardware access for data plane 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.
✓
Assign the VM a virtual function (VF) using SR-IOV on the physical NIC.
Why this is correct
SR-IOV provides near-native performance by giving the VM direct NIC access.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a standard virtual switch with a single vCPU for the VM.
Why it's wrong here
A single vCPU and standard vSwitch will bottleneck throughput.
✗
Enable jumbo frames on the virtual switch only.
Why it's wrong here
Jumbo frames help but do not eliminate the overhead of the virtual switch.
✗
Configure the VM with multiple vNICs and use NIC teaming.
Why it's wrong here
NIC teaming improves redundancy but not per-flow throughput due to virtual switch overhead.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that adding more vNICs or teaming can solve throughput issues, but the real bottleneck is the hypervisor's software switching overhead, which SR-IOV eliminates by providing direct hardware pass-through.
Detailed technical explanation
How to think about this question
SR-IOV leverages PCIe Physical Functions (PFs) and Virtual Functions (VFs) to allow a VM to directly DMA packets to/from the NIC, bypassing the hypervisor's vSwitch entirely. In real-world deployments, this is critical for latency-sensitive workloads like WAN optimization, where even microsecond delays impact TCP throughput. However, SR-IOV requires IOMMU support in the CPU and proper configuration of the VM's vNIC driver to use the VF, and live migration of such VMs is often restricted.
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.
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: Assign the VM a virtual function (VF) using SR-IOV on the physical NIC. — 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. This reduces CPU overhead and latency, enabling the VM to achieve near line-rate throughput on a 10 Gbps link by allowing direct hardware access for data plane 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.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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