5.1 SDN controller types and architectures
3 min read•august 9, 2024
SDN controllers come in various types and architectures, each with unique strengths. Centralized controllers offer simplified management, while distributed designs improve . Hierarchical and clustered approaches balance centralized control with distributed execution for better reliability.
Controllers use different interfaces to communicate. Northbound interfaces connect to apps, southbound to network devices, and east-west between controllers. These interfaces enable network , device management, and inter-controller coordination in SDN environments.
Controller Architectures
Centralized and Distributed Controllers
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- Centralized controllers manage entire network from single point
- Offer simplified management and global network view
- Potential single point of failure and scalability limitations
- Examples include NOX and Floodlight controllers
- Distributed controllers divide control responsibilities across multiple nodes
- Improve scalability and fault tolerance
- Require coordination mechanisms between controller instances
- ONOS and OpenDaylight utilize distributed architectures
Hierarchical and Clustered Approaches
- Hierarchical controllers organize control in multi-level structure
- Top-level controller manages global policies and network-wide view
- Lower-level controllers handle local domain control
- Balances centralized management with distributed execution
- Kandoo framework implements hierarchical SDN control
- Controller clustering groups multiple controller instances
- Operates as single logical entity for improved reliability
- Utilizes consensus algorithms for consistency (Raft, Paxos)
- OpenDaylight supports clustering for high availability
Controller Interfaces
Northbound and Southbound Interfaces
- Northbound interface connects controllers to applications and services
- Enables network programmability and custom control logic
- REST APIs commonly used for northbound communication
- OVSDB protocol facilitates management of Open vSwitch databases
- Southbound interface links controllers to network devices
- Manages communication between control and data planes
- protocol widely adopted for southbound interactions
- Includes device discovery, flow rule installation, and statistics collection
East-West Interface and Inter-Controller Communication
- East-West interface facilitates communication between SDN controllers
- Crucial for distributed and hierarchical architectures
- Enables controller synchronization and state sharing
- SDNi (SDN interface) protocol proposed for standardized east-west communication
- Inter-controller communication supports various functions
- Load balancing across multiple controllers
- Fault tolerance and failover mechanisms
- Consistent network view across distributed
SDN Planes
Control Plane Functions and Components
- Control plane responsible for network intelligence and decision-making
- Determines how traffic should be forwarded through network
- Runs network protocols (OSPF, BGP) for route computation
- Maintains network topology and device state information
- Key control plane components in SDN
- Controller software (NOX, ONOS, OpenDaylight)
- Network applications for specific functions (load balancing, security)
- Policy engines for enforcing network-wide rules
Data Plane Operations and Forwarding
- handles packet forwarding based on control plane decisions
- Consists of network devices (switches, routers) performing actual forwarding
- Utilizes flow tables populated by SDN controller
- Matches incoming packets against flow rules for forwarding actions
- OpenFlow-enabled switches exemplify SDN data plane devices
- Support multiple flow tables for flexible packet processing
- Can perform actions like forwarding, dropping, or modifying packets
- Allow fine-grained control over network behavior
Key Terms to Review (18)
Centralized Controller: A centralized controller is a key component in Software-Defined Networking (SDN) that manages and orchestrates network resources from a single point of control. It enables network administrators to programmatically configure, manage, and optimize the network by separating the control plane from the data plane. This approach allows for greater flexibility, scalability, and efficiency in network management, particularly in environments such as wireless and mobile networks where dynamic resource allocation is essential.
Cloud-Based SDN: Cloud-based SDN refers to the integration of Software-Defined Networking (SDN) with cloud computing environments, enabling centralized network management and resource allocation through a cloud infrastructure. This approach allows for dynamic provisioning of network resources, improved scalability, and enhanced automation, making it easier to manage large-scale networks while leveraging the flexibility of the cloud.
Control plane: The control plane is a fundamental component of network architecture responsible for managing and directing network traffic by controlling the flow of data packets through the network. It separates the decision-making process from the data forwarding process, allowing for more dynamic and efficient network management and enabling features like programmability and automation.
Data Plane: The data plane is the part of a network that carries user data packets from one point to another. It operates on the forwarding of data based on rules set by the control plane, managing how packets are transmitted and processed through the network infrastructure.
Distributed controller: A distributed controller in software-defined networking (SDN) is an architecture where control functions are spread across multiple network devices rather than centralized in a single location. This approach enhances network scalability and resilience by allowing different controllers to operate independently while maintaining communication for coordination. The distributed controller model supports dynamic traffic management and fault tolerance, making it easier to adapt to changing network conditions.
Flexibility: Flexibility refers to the ability of a network architecture to adapt and change in response to varying requirements and conditions. This characteristic is vital in modern networking, enabling rapid adjustments in configurations, resource allocation, and service delivery without extensive manual intervention. Flexibility supports innovation and efficiency by allowing networks to scale, integrate new technologies, and respond dynamically to changing traffic patterns and user demands.
Netconf: NETCONF (Network Configuration Protocol) is a network management protocol used to install, manipulate, and delete the configuration of network devices. It facilitates communication between network management systems and devices by providing a standardized way to configure and manage devices, making it essential in modern network environments.
Network automation: Network automation refers to the use of software and technology to automatically manage and configure network devices and services, minimizing manual intervention. This approach enhances the efficiency, consistency, and reliability of network operations while enabling rapid deployment and changes in network resources.
Network virtualization: Network virtualization is the process of creating a virtual version of a physical network, allowing multiple virtual networks to coexist on the same physical infrastructure. This technology enables greater flexibility, scalability, and efficiency in managing network resources while supporting diverse applications and services.
Northbound API architecture: Northbound API architecture refers to the set of application programming interfaces (APIs) that allow communication between the SDN controller and the applications or services that interact with the network. These APIs are crucial for enabling programmability and automation within software-defined networking by allowing applications to request resources and manage network behavior. They serve as a bridge, making it possible for higher-level applications to influence network operations while abstracting the complexities of the underlying hardware and protocols.
On-Premises SDN: On-premises SDN refers to a software-defined networking architecture that is deployed within an organization’s own physical infrastructure, allowing for direct control and management of the network resources. This setup contrasts with cloud-based or hosted solutions, enabling organizations to customize their networking environments, enhance security, and ensure compliance with internal policies. On-premises SDN provides the advantage of low latency and high performance by utilizing local resources while maintaining the flexibility of software-defined networking principles.
OpenFlow: OpenFlow is a communications protocol that enables the separation of the control and data planes in networking, allowing for more flexible and programmable network management. By using OpenFlow, network devices can be controlled by external software-based controllers, making it a foundational component of Software-Defined Networking (SDN) architectures.
Programmability: Programmability refers to the ability to configure and control network devices and services through software applications, enabling automated and dynamic network management. This concept is crucial in modern networking as it enhances flexibility, allowing for more efficient resource utilization and rapid deployment of new services, which are foundational elements in the evolution of networking architectures.
Scalability: Scalability refers to the ability of a network or system to accommodate growth and handle increased demand without sacrificing performance. In the context of software-defined networking (SDN), scalability is essential as it allows networks to expand seamlessly, integrating new devices and services while maintaining efficient operations.
SDN Orchestration: SDN orchestration refers to the automated management and coordination of network resources and services in a Software-Defined Networking environment. It enables the dynamic provisioning, configuration, and optimization of network elements, ensuring that they work together seamlessly to meet application demands. This orchestration process is crucial for maintaining the efficiency and scalability of networks, connecting it to various SDN controller architectures and programming frameworks that facilitate these tasks.
Security concerns: Security concerns refer to the risks and vulnerabilities associated with the protection of data and resources in a networked environment. In the context of modern networking, particularly with Software-Defined Networking (SDN), these concerns span multiple dimensions including the integrity of data flows, unauthorized access to network resources, and the potential for malicious attacks targeting the control plane and data plane. The dynamic and programmable nature of SDN introduces unique challenges that require careful consideration to ensure robust security measures are in place.
Southbound API Architecture: Southbound API architecture refers to the interface that allows communication between the SDN (Software-Defined Networking) controller and the network devices. This architecture plays a crucial role in enabling the SDN controller to manage and configure the network hardware, which includes switches, routers, and firewalls. It defines how commands and information are exchanged between the controller and the physical or virtual network devices, ultimately enhancing network management and programmability.
Traffic Engineering: Traffic engineering is the process of optimizing the performance and efficiency of data networks by managing the flow of data packets through various paths in the network. It involves techniques that ensure efficient bandwidth utilization, minimize congestion, and improve overall network reliability. Effective traffic engineering allows networks to adapt to changing conditions and demands, enhancing user experience and resource allocation.