The answer is PCI passthrough, which assigns the entire physical PCIe NIC directly to the VM, providing dedicated hardware access with full performance and zero hypervisor overhead. This technology achieves true performance isolation because the VM owns the device exclusively, preventing other VMs from sharing or interfering with it, which is critical for latency-sensitive or high-throughput legacy applications. On the ENCOR 350-401 exam, this concept tests your understanding of virtualization and hardware acceleration features in KVM-based hypervisors, often appearing in scenario-based questions about balancing performance with isolation. A common trap is confusing PCI passthrough with SR-IOV—remember that passthrough gives the entire NIC to one VM, while SR-IOV splits a single NIC into multiple virtual functions for shared use. Memory tip: “Pass through the whole card, not just a part.”
350-401 Virtual Machines and Hypervisors Practice Question
This 350-401 practice question tests your understanding of virtual machines and hypervisors. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 migrating a legacy application from a physical server to a virtual machine on a KVM-based hypervisor. The application requires direct access to a PCIe network interface card for performance reasons. The engineer needs to provide the VM with dedicated hardware access while maintaining isolation from other VMs. Which technology should the engineer use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use PCI passthrough to assign the NIC directly to the VM.
PCI passthrough (Option A) is correct because it assigns the entire physical PCIe NIC directly to the VM, giving it exclusive, dedicated hardware access with full performance and no hypervisor overhead. This meets the requirement for direct access while maintaining isolation, as other VMs cannot use the same device.
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 PCI passthrough to assign the NIC directly to the VM.
Why this is correct
Correct because PCI passthrough gives the VM exclusive access to the physical NIC.
Related concept
Read the scenario before looking for a memorised answer.
✗
Enable SR-IOV and assign a virtual function to the VM.
Why it's wrong here
Incorrect because SR-IOV still uses a shared physical function and hypervisor involvement.
✗
Configure a paravirtualized network driver (virtio).
Why it's wrong here
Incorrect because paravirtualization improves performance but does not provide direct hardware access.
✗
Attach the VM to a Linux bridge using macvtap.
Why it's wrong here
Incorrect because macvtap is a network interface, not a hardware passthrough mechanism.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between PCI passthrough (dedicated, exclusive access) and SR-IOV (shared, but with virtual functions), and the trap here is that candidates may choose SR-IOV thinking it provides 'dedicated' access, when in fact it still involves the PF and is designed for sharing the physical NIC among multiple VMs.
Detailed technical explanation
How to think about this question
PCI passthrough relies on IOMMU (Intel VT-d or AMD-Vi) to map the physical device's memory and interrupts directly to the VM, bypassing the host kernel. This eliminates any hypervisor involvement in data path, achieving near-native performance, but it also means the device cannot be shared with other VMs—a key trade-off. In production, this is often used for latency-sensitive workloads like high-frequency trading or real-time packet processing.
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: Use PCI passthrough to assign the NIC directly to the VM. — PCI passthrough (Option A) is correct because it assigns the entire physical PCIe NIC directly to the VM, giving it exclusive, dedicated hardware access with full performance and no hypervisor overhead. This meets the requirement for direct access while maintaining isolation, as other VMs cannot use the same device.
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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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An architect is designing a virtualized environment for network functions that require direct access to physical NICs for performance. The hypervisor must support PCI passthrough. Which hypervisor type is best suited for this requirement?
easy
✓ A.Type 1 hypervisor (e.g., VMware ESXi or KVM).
B.Type 2 hypervisor (e.g., VirtualBox or VMware Workstation).
C.Container runtime (e.g., Docker).
D.Bare-metal server without virtualization.
Why A: A Type 1 hypervisor (bare-metal) runs directly on the hardware and has direct access to physical resources, including PCIe devices. It supports PCI passthrough (e.g., Intel VT-d or AMD IOMMU), which allows a virtual machine to directly access a physical NIC without hypervisor intervention, maximizing performance for network functions. VMware ESXi and KVM are common Type 1 hypervisors that implement this capability.
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Question Discussion
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