Software-Defined Networking in Modern Networks: A Systematic Literature Review of Architectures, Benefits, and Deployment Challenges (2020–2026)

Software-Defined Networking (SDN) separates network control from packet forwarding and exposes programmable interfaces for policy, automation, and traffic engineering. This article systematically synthesizes research on SDN in modern networks published from 2020 to 2026. The review followed PRISMA 2020 reporting principles and searched SciSpace, Google Scholar, and PubMed. From 1,417 records, 492 duplicates were removed, 925 unique records were ranked, 135 full texts were assessed, and 71 studies were included in the qualitative synthesis. Distributed or hierarchical control was the most frequently reported architecture (48%), followed by centralized (34%) and hybrid arrangements (18%). The most commonly reported benefits were scalability and flexibility (68%), programmability and simplified management (59%), and enhanced security capabilities through centralized visibility (41%). The principal constraints were control-plane scalability (54%), security vulnerabilities (34%), performance limitations under demanding conditions (31%), deployment complexity (27%), and interoperability or standardization deficits (23%). The evidence indicates that SDN is no longer only an experimental networking model; it is an enabling platform for cloud, data-centre, IoT, 5G, wide-area, and vehicular systems. However, dependable adoption requires resilient multi-controller designs, secure control channels, interoperable interfaces, realistic performance validation, and phased migration from legacy infrastructure. The review concludes that hybrid and hierarchical deployments currently offer the most practical balance between centralized programmability and operational resilience.