Here’s an overview of **Software-Defined Networks (SDNs)**:

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### What is a Software-Defined Network (SDN)?

**Software-Defined Networking (SDN)** is an approach to networking that enables centralized, programmable control over the network infrastructure. Unlike traditional networks, where each device (switch, router) makes independent decisions, SDNs separate the control plane (decision-making) from the data plane (traffic forwarding), allowing for more flexible and dynamic network management.

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### Key Concepts

– **Control Plane**: The part of the network responsible for making decisions about where traffic should be sent. In SDN, this is centralized in a controller.
– **Data Plane**: Handles the actual forwarding of packets based on rules from the control plane.
– **SDN Controller**: The centralized software that manages the network, configures devices, and makes routing decisions.
– **Southbound APIs**: Protocols like OpenFlow that communication between the controller and network devices.
– **Northbound APIs**: Interfaces used by applications to communicate with the SDN controller for network management and automation.

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### How SDN Works

1. **Centralized Control**: The SDN controller has a global view of the entire network.
2. **Programmability**: Network administrators can program the controller to change network behavior dynamically.
3. **Flow-based Management**: Traffic is managed through flow rules pushed from the controller to switches.
4. **Dynamic and Flexible**: Changes, policies, and optimizations can be implemented quickly via software.

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### Benefits of SDN

– **Simplified Network Management**: Central control reduces complexity.
– **Rapid Deployment**: New policies and configurations can be executed instantly.
– **Cost Efficiency**: Use of commodity hardware with smart software control.
– **Enhanced Security**: Easier to enforce policies centrally.
– **Network Automation**: Supports dynamic provisioning and adjustment.

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### Use Cases

– Data centers
– Campus networks
– Service provider networks
– Network function virtualization (NFV)
– Cloud environments

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