Which SD-WAN Policy Ensures Voice Uses a Sub-50 ms Link?
Which policy is configured to ensure that a voice packet is always sent on the link with less than a 50 msec delay?
Community Insight
It tests centralized versus localized data policy; the trap is assuming per-interface QoS can enforce an end-to-end delay SLA.
This question tests how Cisco SD-WAN steers voice traffic by WAN link delay. The correct answer is a centralized data policy, which can apply an SLA class requiring less than 50 ms delay across tunnels.
Choosing a localized data policy because it handles interface QoS scheduling or marking, even though it cannot dynamically select a WAN tunnel by measured delay.
Community Discussion (7 comments)
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Expert Analysis
Why the Answer Is Correct
A centralized data policy is configured on the SD-WAN controller and applied per VPN, so it can match voice traffic and invoke an application-aware routing action such as an SLA class with a delay threshold below 50 ms. The WAN Edge then compares tunnel performance against that SLA and forwards voice over a compliant path. This is path selection based on link quality, not merely per-interface queuing or marking. Therefore the policy that can ensure voice uses a sub-50 ms link is the centralized data policy, option D.Why the Other Options Are Wrong
A localized data policy runs on a single WAN Edge and is used for per-interface QoS scheduling, policing, marking, and ACL actions; it does not evaluate end-to-end tunnel delay across the WAN. A centralized control policy operates on control-plane routing and OMP path attributes, not per-flow data forwarding based on delay. A localized control policy affects local control-plane route handling and likewise has no mechanism to steer a voice packet to a tunnel because it meets a 50 ms SLA. Control policies influence which routes exist or are preferred, while the delay-sensitive forwarding decision here belongs to the data policy framework.Community Comment Notes
Several learners, including John662266 and thomazmr, identify D as the forwarding or data-policy answer. Kojy captures the key distinction bluntly: "LOCALIZED DATA POLICY DON'T ENFORCE SLA". donciga likewise notes that a localized policy does not dynamically evaluate link performance SLAs across WAN tunnels. Myare correctly observes that both centralized and localized policies can classify and mark QoS traffic, but that does not make the localized policy capable of delay-based tunnel selection. mikidvd51 and Afshan split between A and D because QoS terminology overlaps with SLA steering; the decisive point remains tunnel selection by delay.Exam Strategy
Read the requirement carefully: per-interface treatment such as marking, policing, or queuing points to a localized data policy, while delay, loss, or jitter thresholds for choosing a WAN path point to a centralized data policy with app-aware routing.
Frequently Asked Questions
Why can't a localized data policy enforce a 50 ms voice SLA?
It provides per-interface QoS, marking, and ACL actions on one edge; it does not evaluate tunnel delay or select a path across the WAN.
Where is the sub-50 ms SLA action configured for voice traffic?
In a centralized data policy on the controller, where voice traffic matches an SLA class whose delay threshold is below 50 ms.
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