While discussing about the modern networking, it will take us through the concepts and technologies of networking which became very popular in the modern era that is the software-defined networking or SDN. As it is called the software-defined networking (SDN), it is such a networking technology where the network services can be created or defined based on the software configuration. SDN is a dynamic technology which is manageable, cost-effective, and adaptable, and that makes it ideal for modern-era applications which have a dynamic nature of work and high-bandwidth requirement. The scope of SDN remains in making the network architecture with a software-centric approach to decouple the network control (control plane) and forwarding functions (data-forwarding plane). This happens in such a manner that the network control becomes dynamic, programmable, and centralized policy control, whereas the underlying infrastructure is abstracted for applications and network services with no manual dependence on physical infrastructure. In general, the network architecture has traditionally the networking devices with combined control and data plane functions into a single hardware entity, typically a router or switch. The control plane is such a network element that determines the interaction among devices within a network. The routing protocols like Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP) and switching protocols like Spanning Tree Protocol (STP) are the control plane protocols that are used, respectively, at routing and switching levels. Using these device-centered control plane protocols, a device determines the suitable device port or interface that is used to forward data at the data plane. In that way, the use of SDN has shifted the control plane from being device centric, that is, at the individual device level to overall network centric.