Software-defined networking (SDN) is an emerging network architecture where network control is decoupled from forwarding and is directly programmable. This migration of control, formerly tightly bound in individual network devices, into accessible computing devices enables the underlying infrastructure to be abstracted for applications and network services, which can treat the network as a logical or virtual entity.

In a traditional network, the control plane and the data plane are vertically integrated. The control plane is responsible for making decisions about where to forward packets, and the data plane is responsible for forwarding the packets. In an SDN network, the control plane is separated from the data plane.

The control plane is centralized in a software-based controller. The controller has a global view of the network and can make decisions about where to forward packets based on a variety of factors, such as the traffic load, the network topology, and the security policy.

The data plane is made up of simple forwarding devices, such as switches and routers. The forwarding devices are responsible for forwarding the packets according to the instructions of the controller.

The SDN architecture is made up of three layers:

• Application Layer: The application layer is where the network applications and services reside. The applications and services can be anything from a simple web server to a complex video streaming service.
• Control Layer: The control layer is where the SDN controller resides. The controller is responsible for managing the network and for making decisions about where to forward packets.
• Infrastructure Layer: The infrastructure layer is where the network devices, such as switches and routers, reside. The network devices are responsible for forwarding the packets according to the instructions of the controller.

There are many different SDN protocols, but the most common protocol is OpenFlow. OpenFlow is a protocol that allows the SDN controller to communicate with the network devices. OpenFlow is an open standard, which means that it is not controlled by any single company.

• Centralized Control: SDN provides centralized control of the network. This makes it easier to manage the network and to make changes to the network.
• Programmability: SDN makes the network programmable. This means that you can write programs to control the network. This can be used to automate tasks, to create new network services, and to improve the performance of the network.
• Agility: SDN makes the network more agile. This means that you can make changes to the network more quickly and easily.
• Innovation: SDN is a new and innovative technology. It has the potential to revolutionize the way that we build and manage networks.

• Security: SDN can be a security risk. If the SDN controller is compromised, then the entire network can be compromised.
• Complexity: SDN can be complex to set up and manage.
• Cost: SDN can be expensive to implement.