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350-401 Infrastructure Practice Question

A network engineer is implementing VXLAN with Cisco SD-Access. The engineer must ensure that the underlay network provides the necessary transport for VXLAN traffic. Which two statements about VXLAN and its underlay are true? (Choose two.)

⚠ Common exam trap

The trap here is assuming VXLAN requires multicast or a Layer 2 underlay, when in fact modern implementations use unicast replication over a Layer 3 underlay.

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

✓

VXLAN uses a 24-bit VNID, allowing over 16 million unique segments.

VXLAN uses a 24-bit VNID for large-scale segmentation and relies on VTEPs to encapsulate traffic. The underlay is typically Layer 3, not Layer 2, and BUM traffic can be handled via multicast or unicast control-plane replication. The two correct statements are the 24-bit VNID and the role of VTEPs.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✓

    VXLAN uses a 24-bit VNID, allowing over 16 million unique segments.

    Why this is correct

    VXLAN encapsulates Layer 2 frames in UDP and uses a 24-bit VXLAN Network Identifier (VNID), which provides up to 16,777,216 unique segments. This scalability is a key advantage over VLANs, which are limited to 4094. The large VNID space supports multi-tenant data centers and large-scale segmentation in SD-Access.

  • ✓

    VXLAN tunnels are established between VTEPs, which can be physical or virtual switches.

    Why this is correct

    VXLAN Tunnel Endpoints (VTEPs) are the devices that encapsulate and decapsulate VXLAN traffic. They can be physical switches, virtual switches, or software VTEPs. In Cisco SD-Access, fabric edge nodes act as VTEPs. This flexibility allows VXLAN to be deployed in various environments, from hardware to virtualized infrastructure.

  • ✗

    VXLAN requires the underlay to be a Layer 2 network with STP.

    Why it's wrong here

    VXLAN is designed to run over a Layer 3 underlay, which provides equal-cost multipathing and eliminates the need for Spanning Tree Protocol. The underlay is typically a routed network with OSPF or IS-IS. Requiring Layer 2 with STP would defeat the purpose of VXLAN and limit scalability.

  • ✗

    VXLAN uses a 12-bit VNID, similar to VLAN IDs.

    Why it's wrong here

    VXLAN uses a 24-bit VNID, not 12-bit. The 12-bit field is used for VLAN IDs, which limits VLANs to 4094. The larger VNID space in VXLAN is a primary reason for its adoption in large-scale networks. Confusing the two sizes is a common error.

  • ✗

    VXLAN requires a multicast-enabled underlay for BUM traffic replication.

    Why it's wrong here

    While early VXLAN implementations used multicast for broadcast, unknown unicast, and multicast (BUM) traffic, modern designs—especially Cisco SD-Access—use unicast replication via a control plane such as LISP or EVPN. Multicast is not a strict requirement; it is one of several options for BUM traffic handling.

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JA

Written and reviewed by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

Last reviewed September 2026 · checked against the official Cisco exam blueprint

This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.