Software-Defined Networking - Architecture

Quiz

Software-Defined Networking (SDN) is used to design, build, and manage networks. Traditional networks depend on hardware. But SDN uses software to control and manage the network. The architecture of SDN is structured and well-defined components and interfaces. These components work together to give you flexibility, centralized control, and efficient network management. Each of these components has a role with their functions, inputs, and outputs. These components are just similar to components of an operating system.

Following are the important components of SDN architecture −

Control Plane
Data Plane
SDN Controller
Application Layer
Infrastructure Layer
Open Interfaces
Network Operating System (NOS)
Programmable Switches

Control Plane

The Control Plane is an important part of SDN. It is used for decisions about how network traffic should be handled. In a traditional network, the control logic is embedded directly into each network device. But, in SDN, the Control Plane is separated from the physical hardware. It is centralized within the SDN controller. So you can have centralized management and easier to configure.

The Control Plane oversees tasks like determining the best path for data, managing network policies, and handling routing protocols. It communicates with the Data Plane to enforce these decisions. The data is forwarded correctly across the network. For example, if a data packet needs to be redirected due to congestion. Then the Control Plane sends instructions to the relevant switches for dynamic adjustments.

Key responsibilities of the Control Plane include −

It manages routing and switching logic.
It determines traffic flows based on policies.
It communicates with the SDN controller to update forwarding rules.
It keeps network-wide policies for optimal data flow.

Data Plane

The Data Plane is also known as the forwarding plane. It is part of the SDN architecture. It is used to handle the actual movement of data through the network. It is composed of network devices like switches and routers that are responsible for forwarding packets based on the instructions received from the Control Plane.

The function of the Data Plane is to execute the forwarding decisions made by the Control Plane in SDN. It does not make any routing decisions on its own. So it is used for simple and cost-effective hardware. For example, a switch in the Data Plane can receive instructions from the SDN controller to forward all packets destined for a specific IP address through a particular port.

Key responsibilities of the Data Plane include −

It forwards packets based on flow rules.
It implements forwarding tables received from the SDN controller.
It executes actions like packet filtering and forwarding as instructed.
It manages data traffic between different network devices efficiently.

SDN Controller

The SDN Controller acts as the "brain" of the SDN architecture. It is similar to a command interpreter in an operating system. It is a software application that centralizes control of the entire network. So administrators can manage network resources.

The SDN Controller communicates with both the Control Plane and Data Plane to gather information about the network state and issue instructions to network devices.

The SDN Controller has a centralized point of control for easier implementation of network policies, traffic management, and security measures. It supports various APIs to interact with network devices, like OpenFlow, REST APIs, and other proprietary protocols. For example the SDN controller can update routing rules across all connected devices for integration, when a new device joins the network.

The SDN Controller is responsible for these activities −

It collects real-time information about network conditions.
It manages flow rules and pushes these to network devices.
It has a user interface or API for administrators to configure network.
You can automate network tasks like configuration updates and policy.

Application Layer

The Application Layer is the topmost layer of the SDN architecture. It is similar to the user-level processes in an operating system. This layer has various applications that use the capabilities of the SDN Controller to perform various tasks, like traffic management, security services, and load balancing.

Applications in this layer communicate with the SDN Controller to request network behavior changes. For example, a security application requests the SDN Controller to block certain types of traffic, and load balancer can direct the SDN Controller to distribute traffic across network paths. So network administrators can deploy and manage tough services without manual changes to each device.

Following are the functions of the Application Layer −

It Requests specific network actions from the controller.
It implements policies like quality of service (QoS) and firewall rules.
You can Automating network configuration for dynamic responses to changing conditions.
It monitors and adjusts network performance based on real-time analytics.

Infrastructure Layer

The Infrastructure Layer is known as the physical layer. It is the foundation of the SDN architecture. It has network devicesboth physical and virtual for Data Plane. These devices like switches and routers are used to forward data according to the instructions of the SDN Controller.

The Infrastructure Layer is analogous to the hardware layer in an operating system. SDN Controller interacts with devices through open interfaces. This separation is used for greater flexibility. Because you can upgrade and replace the physical hardware without affecting the control logic. For example, an organization can replace an old switch with a good one with a higher-capacity model without re-programming the network.

Following are the functions of the Infrastructure Layer −

It forwards data according to flow rules set by the SDN controller.
It supports communication with the SDN controller through open interfaces.
Both physical and virtual network devices to function within an SDN environment.
It integrates new devices seamlessly into the existing network structure.

Open Interfaces

Open Interfaces are an important component of SDN. It is used to communicate between the different layers of the architecture. These interfaces (like OpenFlow, REST APIs) act as channels through which the SDN Controller communicates with the Data Plane devices.

The use of open standards and protocols is used for SDN to be vendor-agnostic. So these devices from different manufacturers work together. Network operators who want to avoid vendor lock-in and build networks that can be adapted as needed. For example, OpenFlow is used for the SDN Controller to install flow rules on switches to tell how packets should be handled.

Functions of Open Interfaces include −

It gives interoperability between devices from different vendors.
It gives the integration of new devices into the network.
It has a standardized way for controllers and network devices to communicate.
You can use custom network applications.

Network Operating System (NOS)

Network Operating System (NOS) is also an important part of SDN architecture. It has software platform that manages and controls the entire network. NOS has an environment where the SDN Controller operates, monitoring network conditions and deciding.

The NOS is used in real-time to view the entire network topology, tracking the status of each device, and giving this information to the SDN Controller. It also manages configuration tasks as changes occur. For example, NOS can reroute traffic to minimize disruptions, when a link fails.

Functions of the Network Operating System include −

Maintain a global view of the network topology.
Manage the distribution of flow rules to all network devices.
Coordinate activities between different SDN applications.
Give APIs for interaction with the SDN Controller and applications.

Programmable Switches

Programmable Switches are used as building blocks of the Data Plane. You can program these switches. SDN Controller manages these switches. So you can upgrade the network easily.

For example, you can instruct a programmable switch to prioritize video streaming traffic over other types of traffic. You can adjust to new traffic patterns, dynamically reallocating resources as needed.

There are various functions of Programmable Switches −

These execute flow rules provided by the SDN Controller.
These forward traffic based on programmable rules.
These support new protocols and functions through software updates.
These improve network performance through intelligent traffic management.

Conclusion

SDN architecture is a structured system that separates network control from data forwarding. It also centralizes decision-making through an SDN Controller using software for network management. It works as an operating system that manages processes, memory, and devices.

SDN manages network traffic, configurations, and data flows. You can create, manage, and scale modern networks. It has flexibility and control that traditional networking cannot match.

With components like the SDN Controller, programmable switches, and open interfaces, SDN has a path for an efficient network.

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