Which SD-WAN Policy Keeps Voice on a Link Below 50 ms Delay?
Which policy is configured to ensure that a voice packet is always sent on the link with less than a 50 msec delay?
Community Votes
50% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The question tests the split between policies that make forwarding/path-selection decisions (centralized data policy with Application-Aware Routing) and policies that only classify, mark, queue or shape traffic locally (localized data policy).
Cisco SD-WAN uses a centralized data policy (Application-Aware Routing) to steer voice packets onto the WAN link whose measured SLA delay stays under 50 ms. This page confirms that the answer is the centralized data policy, not the localized QoS policy many candidates pick.
Choosing the localized data policy (A) because voice immediately suggests QoS; a localized data policy does per-interface classification, marking, policing, shaping and queuing, but it cannot measure per-tunnel delay and select a different link.
Community Discussion (4 comments)
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Expert Analysis
Why the Answer Is Correct
The requirement is link selection based on a live SLA measurement: the voice packet must ride the tunnel whose delay is under 50 ms. In Cisco SD-WAN that is exactly what Application-Aware Routing does — it is defined inside a centralized data policy in vManage, where an SLA class (delay, jitter, loss thresholds such as 50 ms delay) is bound to a match on voice traffic (for example DSCP EF or an application list). The centralized data policy is pushed to the vSmart controllers, which program the vEdge/cEdge routers to probe each transport, compare BFD-based measurements against the SLA class, and forward the matching flow over the compliant tunnel, falling back per the configured action when no path meets the SLA. Because the decision is made centrally and enforced data-plane-wide across the overlay, the centralized data policy is the only option in this list that can guarantee a sub-50 ms delay path for voice.Why the Other Options Are Wrong
A localized data policy (A) is a device-level, interface-specific construct used mainly for QoS: classification, marking, policing, shaping, queuing and mirroring on a single router's interface, so it can prioritise voice once the packet is already on a link but cannot measure delay or redirect the flow to a better link. A centralized control policy (B) governs routing control plane behaviour — topology, TLOC affinity, service insertion, preferred/backup path and control-plane filtering — and does not perform per-flow delay-based data forwarding. A localized control policy (C) is similarly a control-plane construct applied locally (for example OMP route attributes and TLOC preferences) and has no SLA probing or delay threshold. None of B or C can express "< 50 ms delay", which is a data-plane, application-aware statement.Community Comment Notes
Several learners argue for the localized data policy on QoS grounds: as mikidvd51 puts it, "granular QOS for app or prefixes is configured on - localized data policy", and Myare correctly recites that "Classification and Marking" can be done at Layer 2 and Layer 3 — but classification and marking keep a packet on its current path rather than choosing a path that meets a delay budget. John662266 resolves the distinction neatly, noting that the centralized data policy configures the forwarding decision while "local data policy is for QoS", and thomazmr states the same conclusion with "D is correct". The vote split (50/50 between A and D) reflects that QoS vocabulary trap rather than any ambiguity in the requirement itself.Official Reference
Exam Strategy
Read the verb in the requirement before the topic: if the policy must measure a metric and choose a link (delay, jitter, loss, SLA class, best path), it is a centralized data policy with Application-Aware Routing; if it must mark, queue, shape or police traffic on an interface, it is a localized data policy. Memorise the four-policy grid — centralized vs localized control policy for routing/TLOC/control-plane, centralized vs localized data policy for forwarding, AAR and QoS — and this question becomes a one-step lookup.
Frequently Asked Questions
Why is a localized data policy wrong for a 50 ms delay requirement?
A localized data policy only does per-interface QoS (classification, marking, shaping, queuing). It cannot probe tunnels or move the voice flow to a link with lower delay.
How does Application-Aware Routing enforce a delay SLA for voice?
A centralized data policy binds voice traffic to an SLA class; vSmart programs BFD-based probing and the routers forward voice over the tunnel whose delay, jitter and loss meet that class.
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