Software Defined Networking (SDN) is a paradigm that decouples routing functions using a “controller”. The controller is the backbone and heart of an SDN architecture to perform crucial operations related to the control and management of underlying networks.
SDN controller is a very complex segment of the software platform to build and develop numerous applications and provide northbound software APIs. They have a conversation between switches via a command channel to implement network actions such as packet switching with the aid of SDN applications. Some well-known controllers in SDN are :
• NOX
• POX
• RYU
• Floodlight
• OpenDaylight (ODL)
• Open Network Operating System (ONOS)
SDN controllers are widely used for large networks (SD-WAN) where performance is critical. The controller is the most hypercritical SDN network for its ability to monitor and control network traffic flow behavior functions appropriately and smoothly. The two most well-known protocols used by SDN controllers to communicate with switches and routers are,
• OpenFlow
• Open Virtual Switch DataBase (OVSDB).
It provides programmability, virtualization, centralized monitoring and dynamic network control. The controller is the higher critical part of the SDN network to monitor its traffic flow behavior and ensure it functions more properly. SDN controllers have absolute control over a network and are also deployed in large-scale networks performing crucial ones.
• Scalability
• Security
• Consistency
• Reliability.
Scalability:
Scalability canvas the network-s ability to control an enormous amount of traffic. It reflects the efficiency of the SDN controller by handling different forwarding path requests from switches. It had limited resources when it handled an immense amount of requests. The scalability technique dissociates the control plane from the data plane by progressing independently as long as the API connects.
The physically centralized controllers attempt to achieve scalability by breaking the control plane into horizontally distributed or hierarchically organized controllers. For better scalability, the logically-centralized controller must be physically distributed rather than operating on a peer-to-peer basis.
Consistency:
The centralized controller has to assure consistent forwarding during network policy updates. The distributed control architecture consistency involves three categories, such as :
• State consistency
• Rules update consistency
• Version update consistency.
Reliability:
Reliability concern to resilience in both SDN control and data plane. It also refers to performing seamless network operations even if the primary controller breaks down, whereas, in the data plane, it means resilient connectivity in the middle of forwarding nodes. Reliability plays a vital key role in software development.
The configuration of the SDN controller must be intelligent and validate network management to improve network availability that can be prevented and handle errors.
Security:
SDN, which affects overall network security and performance. Security is at the forefront of these challenges. A centralized controller is responsible for managing the entire network, while security compromise of the entire controller section can render the whole network compromised.
