Which SD-WAN Policy Ensures Voice Uses a Sub-50 ms Link?
Short answer
D A centralized data policy with an SLA class requiring delay under 50 ms steers voice traffic to a compliant WAN tunnel.
Question
Key Takeaways
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.
Common mistake: 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.
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?
Where is the sub-50 ms SLA action configured for voice traffic?
Discussion 7 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 7
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mikidvd51 👍 4 Answered Agranular QOS for app or prefixes is configured on - localized data policy
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Myare 👍 2 Answered Athe QoS configuration process is to assign traffic flows coming from the service-side to the appropriate forwarding classes. We can do this with either a centralized data policy on a per-VPN basis or with a localized data policy on a per-interface basis. Classification and Marking can be done at different network layers: Layer 2: 802.1q, MPLS EXP Layer 3: IP precedence, DSCP, IP ECN, Source/Destination IP Layer 4: TCP/UDP ports Layer 7: DPI/NBAR
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Afshan 👍 2 Answered DSince the policy is Network wide and not to specific Edge, I believe it is Centralized. And since the policy is on the traffic I believe it is a Data Policy.
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John662266 👍 2 Answered Dit should be use centralized data policy configure forward policy. local data policy is for QoS ..
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thomazmr 👍 2 Answered DD is correct
Show 2 more comments
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donciga 👍 1A. localized data policy: While used for localized data plane actions like Quality of Service (QoS) scheduling, policing, and access-control lists (ACLs) per interface, it does not dynamically evaluate link performance SLAs across WAN tunnels.
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Kojy 👍 1 Answered DCORRECT IS D .........LOCALIZED DATA POLICY DON'T ENFORCE SLA
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