The answer is to enable SR-IOV on the physical NIC and assign virtual functions to the VM. This is correct because SR-IOV, or Single Root I/O Virtualization, allows a physical NIC to present multiple virtual functions directly to a VM, bypassing the hypervisor’s virtual switch entirely. By eliminating the software switching layer, SR-IOV dramatically reduces latency and CPU overhead, which is essential for high-throughput, low-latency VNFs like the CSR1000v. On the ENCOR 350-401 exam, this scenario tests your understanding of how to optimize network performance for virtualized network functions, often contrasting SR-IOV with other options like NetFlow or port mirroring, which add overhead rather than reduce it. A common trap is to assume that any advanced NIC feature will improve performance, but only SR-IOV provides near-native hardware access by assigning VFs directly to the VM. Memory tip: think “SR-IOV = Skip the vSwitch” to recall that it bypasses the hypervisor’s virtual switch for direct NIC access.
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.
A company is deploying a virtualized router (CSR1000v) on VMware vSphere. The VNF must support high throughput and low latency. Which vSphere configuration option should the architect select to optimize network performance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable SR-IOV on the physical NIC and assign virtual functions to the VM.
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 latency and CPU overhead, making it ideal for high-throughput, low-latency VNFs like the CSR1000v. Option B is correct because SR-IOV provides near-native performance by allowing the VM to directly access the NIC hardware.
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.
✗
Use the default e1000 NIC driver.
Why it's wrong here
e1000 is a legacy driver with lower performance.
✓
Enable SR-IOV on the physical NIC and assign virtual functions to the VM.
Why this is correct
SR-IOV provides near-native performance by direct hardware access.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use VMXNET3 paravirtualized NIC.
Why it's wrong here
VMXNET3 is better than e1000 but still involves hypervisor overhead.
✗
Configure the VM with multiple vCPUs and large memory.
Why it's wrong here
CPU and memory alone do not optimize network I/O performance.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that VMXNET3 is the best performance option for all VNFs, but the trap here is that SR-IOV is required when the question explicitly demands 'high throughput and low latency' because it eliminates hypervisor overhead.
Detailed technical explanation
How to think about this question
SR-IOV works by partitioning a physical NIC into multiple PCIe virtual functions (VFs) that are assigned directly to VMs via PCI passthrough. The CSR1000v can leverage DPDK (Data Plane Development Kit) when using SR-IOV to further accelerate packet processing by polling VFs in user space, bypassing kernel interrupts. In real-world deployments, SR-IOV is critical for VNFs handling line-rate traffic, such as virtual routers or firewalls, where even microsecond latency matters.
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.
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: Enable SR-IOV on the physical NIC and assign virtual functions to the VM. — 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 latency and CPU overhead, making it ideal for high-throughput, low-latency VNFs like the CSR1000v. Option B is correct because SR-IOV provides near-native performance by allowing the VM to directly access the NIC hardware.
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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