RetroFlow: Maintaining Control Resiliency and Flow Programmability for Software-Defined WANs

TL;DR

RetroFlow enhances SDN WAN resilience by intelligently remapping offline switches to active controllers, significantly reducing communication overhead during controller failures without disrupting normal controller operations.

Contribution

RetroFlow introduces a novel method for controlling offline switches in SDN WANs, maintaining flow programmability and reducing communication overhead during controller failures.

Findings

Reduces communication overhead by up to 52.6% during moderate failures.

Achieves up to 61.2% reduction during severe failures.

Recovers 90-100% of flows from offline switches.

Abstract

Providing resilient network control is a critical concern for deploying Software-Defined Networking (SDN) into Wide-Area Networks (WANs). For performance reasons, a Software-Defined WAN is divided into multiple domains controlled by multiple controllers with a logically centralized view. Under controller failures, we need to remap the control of offline switches from failed controllers to other active controllers. Existing solutions could either overload active controllers to interrupt their normal operations or degrade network performance because of increasing the controller-switch communication overhead. In this paper, we propose RetroFlow to achieve low communication overhead without interrupting the normal processing of active controllers during controller failures. By intelligently configuring a set of selected offline switches working under the legacy routing mode, RetroFlow relieves the active controllers from controlling the selected offline switches while maintaining the flow programmability (e.g., the ability to change paths of flows) of SDN. RetroFlow also smartly transfers the control of offline switches with the SDN routing mode to active controllers to minimize the communication overhead from these offline switches to the active controllers. Simulation results show that compared with the baseline algorithm, RetroFlow can reduce the communication overhead up to 52.6% during a moderate controller failure by recovering 100% flows from offline switches and can reduce the communication overhead up to 61.2% during a serious controller failure by setting to recover 90% of flows from offline switches.