SDN Traffic Engineering Model with BGP-LSP
A software-defined networking (SDN) controller learns network topology information by using BGP link-state sessions with the route reflectors of an MPLS-enabled network. The controller then uses the topology information to apply on-demand traffic policies to the network through a protocol that is supported from all Layer 3 routers. Each policy is represented as a RIB entry in the control plane of the router. Which SDN model has been implemented?
Community Votes
53% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
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.
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.
Community Discussion (6 comments)
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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?
Centralized SDN often implies replacing distributed control planes entirely. Here, routers still run BGP/MPLS and maintain RIBs, indicating a collaborative TE approach rather than full centralization.
Is SDN Hybrid a valid model here?
While some argue for Hybrid, Cisco exams typically categorize this specific BGP-LS + Controller setup as Traffic Engineering. Hybrid usually refers to mixing cloud and on-prem management styles.