The correct choice is the Linux bridge with VLAN tagging enabled on the bridge interface, because it delivers a standard Layer 2 forwarding path with native 802.1Q VLAN trunking support, allowing VNFs to communicate with minimal overhead. Unlike more complex virtual switches, the Linux bridge operates entirely in kernel space, eliminating userspace processing and reducing latency—critical for KVM-based NFV deployments where performance and simplicity are paramount. On the ENCOR 350-401 exam, this question tests your understanding of virtual networking models for network functions virtualization, often contrasting the Linux bridge against Open vSwitch or macvtap. A common trap is assuming that VLAN trunking requires a full-featured switch like OVS, but the Linux bridge natively supports VLAN filtering on the bridge interface itself. Memory tip: think “kernel-native trunking” — the Linux bridge is the lightweight, low-overhead choice for KVM NFV because it keeps VLAN tagging in the kernel, not in userspace.
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.
An enterprise is deploying a KVM-based virtualization platform for network functions. The architect must choose a networking model that allows VNFs to communicate with minimal overhead and supports VLAN trunking. Which virtual networking component should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Linux bridge with VLAN tagging enabled on the bridge interface.
A Linux bridge with VLAN tagging enabled on the bridge interface is the correct choice because it provides a standard Layer 2 forwarding path with native 802.1Q VLAN trunking support, allowing VNFs to communicate with minimal overhead. Unlike more complex solutions, the Linux bridge operates in kernel space with low latency and does not require additional userspace processing, making it ideal for KVM-based NFV deployments where performance and simplicity are key.
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.
✓
Linux bridge with VLAN tagging enabled on the bridge interface.
Why this is correct
This provides VLAN trunking and low-overhead connectivity for VNFs.
Related concept
Read the scenario before looking for a memorised answer.
✗
macvtap in bridge mode, which bypasses the Linux bridge.
Why it's wrong here
macvtap does not support VLAN trunking natively and may not meet requirements.
✗
Open vSwitch with DPDK for maximum performance.
Why it's wrong here
While high-performance, OVS with DPDK adds complexity and may be overkill for basic trunking.
✗
Host-only networking with NAT to isolate VNFs.
Why it's wrong here
Host-only networking does not provide VLAN trunking to external networks.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that macvtap in bridge mode is a drop-in replacement for a Linux bridge, but it fails to support VLAN trunking because it does not expose a bridge interface for VLAN filtering on the host.
Detailed technical explanation
How to think about this question
Under the hood, the Linux bridge implements the IEEE 802.1D standard and can be configured with VLAN filtering using the `bridge vlan` command, which allows per-port VLAN membership and trunking. In a real-world scenario, an enterprise might use this setup to connect VNFs (e.g., virtual routers or firewalls) to different tenant VLANs without needing a separate physical NIC per VLAN, leveraging the bridge's ability to forward tagged frames directly to the VM's virtio-net interface.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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: Linux bridge with VLAN tagging enabled on the bridge interface. — A Linux bridge with VLAN tagging enabled on the bridge interface is the correct choice because it provides a standard Layer 2 forwarding path with native 802.1Q VLAN trunking support, allowing VNFs to communicate with minimal overhead. Unlike more complex solutions, the Linux bridge operates in kernel space with low latency and does not require additional userspace processing, making it ideal for KVM-based NFV deployments where performance and simplicity are key.
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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