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Difficulty: Very hardComparing Traditional Networks with Controller-Based Networking

An enterprise network operations team is executing a digital transformation project to migrate a legacy campus environment using per-device CLI management and distributed control protocols (OSPF and STP) to a software-defined controller-based network using Cisco DNA Center. During the architectural review, engineers evaluate how device provisioning, control plane mechanics, and API interactions differ between traditional distributed models and centralized controller-based fabrics. Which two of the following statements accurately describe key operational and architectural distinctions between traditional and controller-based networking?

  1. Control plane policy definition is centralized at the controller, which abstracts physical topology details and uses Southbound APIs to push programmatic configurations across network devices.Answer
  2. Northbound REST APIs allow external management applications and automation scripts to programmatically interact with the SDN controller rather than directly communicating with individual network switches.Answer
  3. C
    The controller uses RESTful HTTP POST requests over its Southbound Interface to continuously read and retrieve operational metrics and interface statistics from switches without modifying device state.
  4. D
    Controller-based management requires dedicated software agents to be pre-installed on each network switch to execute SSH-based policy translation scripts sent by the control plane.

Answer

The two correct statements state that control plane policy definition is centralized at the controller using Southbound APIs to manage data-plane devices, and that Northbound REST APIs allow applications to programmatically interact with the controller rather than individual switches.
In controller-based networking, the centralized controller decouples intent and policy management from individual physical hardware. It relies on Southbound APIs (e.g., NETCONF, RESTCONF, OpenFlow) to program data-plane network devices and exposes Northbound REST APIs to enable higher-level applications and scripts to automate network-wide operations without direct CLI manipulation of individual nodes.

Step-by-Step Solution

1
Analyze control plane separation and API roles in SDN architectures.
Centralized SDN controllers abstract management and control plane functions, using Southbound APIs (e.g., NETCONF/RESTCONF) to communicate down to physical infrastructure and Northbound APIs (RESTful HTTP) to communicate up to applications.
This establishes the fundamental architectural boundary between Northbound and Southbound interfaces in controller-based networking.
2
Evaluate the HTTP verb mapping for telemetry retrieval.
Retrieving data uses the HTTP GET method, while HTTP POST creates resources.
Mapping HTTP POST to state retrieval represents a fundamental CRUD misinterpretation in RESTful interface operations.
3
Evaluate switch management requirements and agent architectural models.
Cisco controller architectures utilize agentless Southbound management protocols rather than installing local software agents on switch operating systems.
Differentiating agent-based configuration models (e.g., Puppet/Chef) from standard SDN agentless protocol interfaces is critical when comparing traditional vs SDN environments.

Key Concept

Centralized SDN Architectures, Control/Data Plane Separation, and Northbound vs Southbound APIs
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Topics

Comparing Traditional Networks with Controller-Based Networking

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