A software-defined network (SDN) separates the network control plane from the data forwarding plane. SDN has shown significant benefits in many ways compared to conventional non-SDN networks. However, traffic distribution in SDN impacts efficiency and raises many other challenges. For instance, uneven load distribution in the SDN significantly impacts the network performance. Hence, several SDN load balancing (LB) techniques have been introduced to improve the efficiency of SDN. In this article, we provide a thematic taxonomy of LB in SDN, considering several parameters from the past technical studies such as the objectives of LB, data plane LB techniques, control plane LB techniques, other aspects of data plane/control plane LB as well as the performance metrics for LB techniques. Furthermore, useful insights on LB and a comparative analysis of various promising SDN LB techniques are also included in the survey. Finally, existing challenges and future direction on SDN LB techniques are highlighted.

软件定义网络（SDN）将网络控制平面与数据转发平面分开。与传统的非SDN网络相比，SDN在许多方面都显示出显着的优势。但是，SDN中的流量分配会影响效率并带来许多其他挑战。例如，SDN中负载分布不均会严重影响网络性能。因此，已经引入了几种SDN负载平衡（LB）技术来提高SDN的效率。在本文中，我们考虑了过去技术研究中的几个参数，例如LB的目标，数据平面LB技术，控制平面LB技术以及数据平面/控制平面LB的其他方面，提供了SDN中LB的主题分类法。作为LB技术的性能指标。此外，调查还包括对LB的有用见解以及对各种有前途的SDN LB技术的比较分析。最后，强调了SDN LB技术的现有挑战和未来方向。