The answer is that the static MAC address was not within the allowed range for Hyper-V virtual machines. Hyper-V enforces a strict OUI-based range for static MAC addresses, defaulting to 00-15-5D-XX-XX-XX, which corresponds to Microsoft’s assigned prefix. Any address outside this range—such as one starting with a different vendor OUI—will be rejected by the hypervisor, preventing the virtual NIC from functioning even if the address is unique on the network. On the ENCOR 350-401 exam, this tests your understanding of virtualization platform constraints versus general networking; a common trap is assuming any valid unicast MAC will work, when Hyper-V specifically blocks non-Microsoft OUIs for static assignments. Remember the mnemonic “Hyper-V Hates Outside OUIs” to recall that only the 00-15-5D prefix is permitted by default.
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 engineer is configuring a virtual machine on a Microsoft Hyper-V host. The VM runs a legacy application that requires a static MAC address. The engineer sets the MAC address in the VM settings. After the VM starts, the application cannot communicate on the network. The engineer verifies that the MAC address is not duplicated on the network. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The static MAC address is not within the allowed range for Hyper-V virtual machines.
Hyper-V enforces a specific range for static MAC addresses assigned to virtual machines. The default allowed range is 00-15-5D-XX-XX-XX, derived from the Microsoft Organizationally Unique Identifier (OUI). If the engineer configured a MAC address outside this range (e.g., starting with a different OUI), Hyper-V will not allow the VM to use it, effectively breaking network communication even though the address is not duplicated on the network.
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.
✓
The static MAC address is not within the allowed range for Hyper-V virtual machines.
Why this is correct
Correct because Hyper-V enforces a specific MAC address range for static assignments to avoid conflicts.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The VM is configured to use a dynamic MAC address, overriding the static setting.
Why it's wrong here
Incorrect because Hyper-V allows static MAC addresses when configured.
✗
The VM's network adapter is set to use the legacy network adapter type.
Why it's wrong here
Incorrect because legacy adapters also support static MAC addresses.
✗
The VM is a generation 2 VM, which does not support static MAC addresses.
Why it's wrong here
Incorrect because generation 2 VMs support static MAC addresses.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that any static MAC address can be assigned to a Hyper-V VM, when in reality the address must fall within the Microsoft OUI range (00-15-5D-XX-XX-XX) to be accepted by the hypervisor.
Detailed technical explanation
How to think about this question
Hyper-V uses the Microsoft OUI 00-15-5D for automatically generated MAC addresses, but it also reserves a specific range (00-15-5D-00-00-00 to 00-15-5D-FF-FF-FF) for static assignments. If a static MAC address falls outside this range, the Hyper-V virtual switch may reject the address or fail to bind it to the virtual NIC, causing the VM to have no valid Layer 2 connectivity. This behavior is enforced at the hypervisor level, not by the guest OS, which is why the application cannot communicate despite the address being unique on the network.
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: The static MAC address is not within the allowed range for Hyper-V virtual machines. — Hyper-V enforces a specific range for static MAC addresses assigned to virtual machines. The default allowed range is 00-15-5D-XX-XX-XX, derived from the Microsoft Organizationally Unique Identifier (OUI). If the engineer configured a MAC address outside this range (e.g., starting with a different OUI), Hyper-V will not allow the VM to use it, effectively breaking network communication even though the address is not duplicated on the network.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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