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Difficulty: Very hardComparing Traditional Networks with Controller-Based Networking

A network architect is comparing the convergence and operational behavior of a legacy campus environment running distributed routing protocols against a controller-based Software-Defined Networking (SDN) fabric. Following an unexpected link failure within the core infrastructure, which statement correctly contrasts how control plane state and data plane forwarding updates are processed in the controller-based architecture versus the traditional distributed network model?

  1. The centralized controller recalculates the network topology and updates device forwarding tables via Southbound interface protocols, whereas traditional routers individually compute routing algorithms locally to update their own forwarding tables.Answer
  2. B
    The controller uses HTTP GET requests across Northbound REST APIs to dynamically alter data plane MAC address tables on switch hardware, whereas traditional routers rely on TACACS+ to synchronize distributed control plane states.
  3. C
    The controller relies on an agentless orchestration engine to execute automated scripts that forward frame-by-frame data plane packets, whereas traditional switches rely on agent-based hypervisors to handle local packet forwarding.
  4. D
    The controller intercepts all data plane traffic and processes low-level packet switching directly through Syslog severity level 7 emergency messages, whereas traditional switches decouple the control plane to achieve sub-second convergence.

Answer

The centralized controller recalculates the network topology and updates device forwarding tables via Southbound interface protocols, whereas traditional routers individually compute routing algorithms locally to update their own forwarding tables.
The correct answer accurately describes the fundamental distinction: controller-based networks centralize control plane logic within an SDN controller that programs data plane switches via Southbound APIs, whereas traditional networks use a distributed control plane where each node independently computes paths and populates its local forwarding table.

Step-by-Step Solution

1
Analyze the control plane architecture of traditional networking.
In traditional networking, each router and switch maintains a distributed control plane. Devices independently run routing protocols (e.g., OSPF, EIGRP), compute shortest paths locally, and populate their own Routing Information Base (RIB) and Forwarding Information Base (FIB).
Understanding distributed control plane mechanics is essential for contrasting traditional architectures with SDN.
2
Analyze the control plane architecture of controller-based networking (SDN).
In controller-based networking, the control plane functions are centralized into an SDN controller (e.g., Cisco DNA Center / SD-Access). The controller possesses a global view of the network, computes paths centrally, and uses Southbound APIs (e.g., NETCONF, RESTCONF, gRPC, OpenFlow) to program the data plane (FIB) of individual network nodes.
Centralized control plane separation and Southbound API programming are the defining architectural characteristics of SDN.
3
Compare response to link failures and topology state updates in both architectures.
During a topology change, an SDN controller updates its central topology map and pushes updated forwarding tables down to devices via Southbound APIs. In contrast, traditional routers flood Link-State Advertisements (LSAs) or update messages and individually re-run local SPF calculations.
This direct comparison isolates the core functional difference during network failure events.

Key Concept

Centralized vs. Distributed Control Plane Architecture and Southbound API Integration
Estimated Time:2m 0s
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Topics

Comparing Traditional Networks with Controller-Based Networking

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