SDN Traffic Engineering Model with BGP-LSP
Short answer
B The SDN traffic engineering model is implemented when a controller uses topology info to apply on-demand traffic policies as RIB entries.
Question
Key Takeaways
Tests the distinction between SDN use cases (like traffic engineering) and architectural models (centralized/hybrid). The trap is confusing the 'controller' aspect with the 'model' definition, ignoring that TE is the specific function described.
Identifies the SDN traffic engineering model where a controller uses BGP link-state to learn topology and applies policies as RIB entries. This page explains why traffic engineering is the correct classification over centralized or hybrid models.
Common mistake: Most candidates choose D (SDN Hybrid) because they associate the presence of a central controller with hybrid architectures, failing to recognize that the question describes a specific functional use case (traffic engineering) rather than an architectural split.
Expert Analysis
Why the Answer Is Correct
The scenario describes a classic SDN Traffic Engineering model. In this model, a central controller collects network state (via BGP-LS) and computes optimal paths, then pushes these as policies (RIB entries) to routers. While it involves a controller, the defining characteristic is the application of on-demand traffic policies for optimization, which is the definition of Traffic Engineering in SDN contexts.
Why the Other Options Are Wrong
SDN Centralized (A) implies a single point of control replacing distributed routing logic entirely, often using protocols like OpenFlow. Here, routers still maintain RIB entries and participate in MPLS/BGP, suggesting a more collaborative approach typical of TE. SD-WAN (C) refers to wide-area network abstraction, not MPLS core topology management. SDN Hybrid (D) is often considered a distractor; while some definitions exist, Cisco exam doctrine typically classifies this specific BGP-LS + PCE/Controller pattern under Traffic Engineering as a primary use case/model.
Community Comment Notes
Community comments highlight the debate between B and D. As one user noted, "SDN TE is not a SDN model - its a use case," reflecting the confusion. However, another comment correctly identifies the technology: "What is being described is SR-TE with ODN" (On-Demand Next). The consensus leans towards D due to ambiguity, but the technical description aligns best with the Traffic Engineering functionality.
Exam Strategy
Focus on the function described: if the goal is optimizing traffic flow using collected topology data, think Traffic Engineering first. Don't default to 'Hybrid' just because a controller exists; look for keywords like 'on-demand', 'optimization', and 'RIB entry'.
Frequently Asked Questions
Why isn't this SDN Centralized?
Is SDN Hybrid a valid model here?
Community Votes
53% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 6 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 6
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cisco_guy 👍 6 Answered BWhat is being described is SR-TE with ODN. https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k-r7-9/segment-routing/configuration/guide/b-segment-routing-cg-asr9000-79x/configure-sr-te-policies.html#:~:text=Segment%20Routing%20On%2DDemand%20Next,required%20(on%2Ddemand).
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i9t6 👍 3 Answered DHybrid, the "On demand" can be interpreted as "allowing policy to be managed in a more centralized manner" https://learningnetwork.cisco.com/s/question/0D53i00000KsuxaCAB/sdn-models-doubts
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anonymousch 👍 3 Answered DSDN Hybrid is the correct answer.
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sandccie 👍 2 Answered DD. SDN TE is not a SDN model - its a use case.
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kalulosu 👍 1 Answered BI think ans is B. It falls under the traffic engineering model of SDN, where the SDN controller leverages network topology information to apply traffic policy, which is reflected as RIB entries in the router's control plane, for traffic optimization and efficient routing. This model is used to manage traffic across the entire network. This model is a focused approach to traffic management and optimization across the entire network.
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Redrum702 👍 1 Answered AAnswer is A: SDN Centralized Model: Description: A single, central controller manages the entire network, maintaining a global view of the topology and making control decisions. Use Case: Simplified management, dynamic traffic engineering, and policy enforcement.
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