  Context: The increase in Internet of Things (IoT) devices gives rise to an
increase in deceptive manipulations by malicious actors. These actors should be
prevented from targeting the IoT networks. Cybersecurity threats have evolved
and become dynamically sophisticated, such that they could exploit any
vulnerability found in IoT networks. However, with the introduction of the
Software Defined Network (SDN) in the IoT networks as the central monitoring
unit, IoT networks are less vulnerable and less prone to threats. %Although,
the SDN itself is vulnerable to several threats.
  Objective: To present a comprehensive and unbiased overview of the
state-of-the-art on IoT networks security enhancement using SDN controllers.
  Method: We review the current body of knowledge on enhancing the security of
IoT networks using SDN with a Systematic Mapping Study (SMS) following the
established guidelines.
  Results: The SMS result comprises 33 primary studies analyzed against four
major research questions. The SMS highlights current research trends and
identifies gaps in the SDN-IoT network security.
  Conclusion: We conclude that the SDN controller architecture commonly used
for securing IoT networks is the centralized controller architecture. However,
this architecture is not without its limitations. Additionally, the predominant
technique utilized for risk mitigation is machine learning.
