  Blockchain (BC) and Software-Defined Networking (SDN) are leading
technologies which have recently found applications in several network-related
scenarios and have consequently experienced a growing interest in the research
community. Indeed, current networks connect a massive number of objects over
the Internet and in this complex scenario, to ensure security, privacy,
confidentiality, and programmability, the utilization of BC and SDN have been
successfully proposed. In this work, we provide a comprehensive survey
regarding these two recent research trends and review the related
state-of-the-art literature. We first describe the main features of each
technology and discuss their most common and used variants. Furthermore, we
envision the integration of such technologies to jointly take advantage of
these latter efficiently. Indeed, we consider their group-wise utilization --
named BC-SDN -- based on the need for stronger security and privacy.
Additionally, we cover the application fields of these technologies both
individually and combined. Finally, we discuss the open issues of reviewed
research and describe potential directions for future avenues regarding the
integration of BC and SDN.
  To summarize, the contribution of the present survey spans from an overview
of the literature background on BC and SDN to the discussion of the benefits
and limitations of BC-SDN integration in different fields, which also raises
open challenges and possible future avenues examined herein. To the best of our
knowledge, compared to existing surveys, this is the first work that analyzes
the aforementioned aspects in light of a broad BC-SDN integration, with a
specific focus on security and privacy issues in actual utilization scenarios.
