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350-401 Practice Question: Deploying a virtualized network function (VNF) on…
A company is deploying a virtualized network function (VNF) on a KVM-based host. The VNF requires dedicated CPU cores and must avoid performance interference from other VMs. Which hypervisor configuration best meets these requirements?
⚠ Common exam trap
Cisco often tests the distinction between hypervisor-agnostic concepts (like CPU pinning) and vendor-specific features (like VMware DRS), and the trap here is that candidates may choose VMware options even when the question explicitly specifies a KVM-based host.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure CPU pinning and use dedicated NUMA nodes.
CPU pinning binds the VNF's vCPUs to specific physical cores, ensuring dedicated CPU resources and preventing interference from other VMs. Using dedicated NUMA nodes further optimizes memory locality, reducing latency and avoiding cross-NUMA memory access, which is critical for performance-sensitive VNFs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable CPU overcommitment and use a single NUMA node.
Why it's wrong here
CPU overcommitment assigns multiple vCPUs to the same physical core, resulting in contention for execution resources, cache thrashing, and scheduling latency spikes. A single NUMA node reduces remote memory access but severely limits total CPU capacity and memory bandwidth, creating a resource bottleneck. For packet-intensive VNF workloads, this violates the requirement for determinism and leads to unacceptable packet drops or jitter.
- ✓
Configure CPU pinning and use dedicated NUMA nodes.
Why this is correct
CPU pinning binds each vCPU to a dedicated physical core, eliminating run-queue contention and preventing unwanted context switches, which guarantees consistent processing capacity. Dedicated NUMA nodes ensure that the memory nearest to those pinned cores is exclusively used, avoiding the increased latency and reduced bandwidth of cross-NUMA memory access. Together, these measures provide deterministic, line-rate performance essential for production NFV deployments.
- ✗
Use VMware vSphere with DRS set to Aggressive.
Why it's wrong here
vSphere DRS with an Aggressive aggressiveness level triggers frequent and rapid VM migrations to balance cluster load, using vMotion. Each migration incurs CPU cache cold misses, memory copying overhead, and a temporary network interruption, all of which disrupt real-time VNF traffic. Worse, vMotion can relocate a VNF to a different NUMA node, silently breaking memory locality and causing severe performance degradation that system administrators cannot easily predict or control.
- ✗
Deploy the VNF as a container instead of a VM.
Why it's wrong here
Deploying the VNF as a container instead of a VM does not inherently solve CPU or memory placement challenges; containers share the host kernel and its scheduler, which can introduce unwanted neighbor interference despite cgroup isolation. While containers can be pinned to specific cores, they still lack the dedicated hardware-level isolation and NUMA awareness that a VM with explicit CPU pinning and dedicated NUMA nodes provides. In NFV, the goal is not simply lower overhead but deterministic isolation, which the container model fails to guarantee on its own.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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