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350-401 Practice Question: A network team is designing QoS for a Cisco…

A network team is designing QoS for a Cisco SD-WAN fabric connecting multiple branch offices to a central data center. The design must ensure that VoIP traffic from branch sites receives priority treatment across the WAN overlay, regardless of the underlying transport (MPLS, Internet, LTE). Which architectural component should the team configure to enforce consistent QoS policies across all WAN edges?

⚠ Common exam trap

Cisco often tests the misconception that QoS policies must be configured locally on each router (Option B) or that RSVP is required for guaranteed service in SD-WAN, but the key is that SD-WAN centralizes QoS management via vManage and vSmart to ensure consistency across all transports.

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 a centralized QoS policy on vManage that matches VoIP DSCP markings and applies priority queuing on all WAN edge routers.

VManage serves as the centralized SD-WAN management plane, allowing administrators to define a single QoS policy that matches VoIP DSCP markings (e.g., EF for expedited forwarding) and applies priority queuing across all WAN edge routers. This ensures consistent treatment of VoIP traffic over any transport (MPLS, Internet, LTE) by pushing the policy to all vEdge/cEdge devices via the vSmart controller, leveraging the SD-WAN overlay's ability to enforce QoS independently of the underlying physical transport.

Answer analysis

Option-by-option breakdown

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

  • ✓

    Configure a centralized QoS policy on vManage that matches VoIP DSCP markings and applies priority queuing on all WAN edge routers.

    Why this is correct

    Centralized QoS policies in Cisco SD-WAN are defined in vManage and propagated by vSmart to every WAN edge router, ensuring identical classification and scheduling behavior across all transports. Matching VoIP DSCP EF markings and assigning them to a priority queue in the policy reduces latency and jitter for real-time traffic, which is the architecturally correct approach for fabric-wide uniformity.

  • ✗

    Define a localized QoS policy on each branch router using MQC, matching the same DSCP values.

    Why it's wrong here

    While MQC can define class maps and policy maps locally on each router, doing so per branch in an SD-WAN fabric introduces scalability challenges and configuration drift, as every device must be touched individually. Localized policies are intended for device-specific, interface-level actions, not for enforcing consistent DSCP-based treatment across the entire overlay, so this approach fails the requirement for centralized control.

  • ✗

    Use the vSmart controller to apply QoS policy only on the MPLS transport, leaving Internet and LTE unmanaged.

    Why it's wrong here

    The vSmart controller does not itself apply QoS; it distributes centralized policies from vManage to edge devices, and those policies are transport-agnostic, affecting MPLS, Internet, or LTE alike. Limiting QoS to the MPLS transport while leaving other transports unmanaged would allow VoIP packets on broadband or LTE to suffer loss and delay, breaking the enterprise requirement for consistent voice quality across every WAN path.

  • ✗

    Implement QoS using RSVP across the overlay tunnels.

    Why it's wrong here

    RSVP (Resource Reservation Protocol) is not used in Cisco SD-WAN for QoS enforcement; the overlay uses IPsec tunnels, and RSVP signaling across them does not integrate with the SD-WAN controller hierarchy. Even if RSVP were deployed, it only reserves bandwidth per flow on physical links, not the centralized, class-based priority queuing needed to guarantee VoIP DSCP treatment across multiple transports, making it both unsupported and architecturally incompatible.

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Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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