# BFT Protocols for Heterogeneous Resource Allocations in Distributed SDN Control Plane

## TL;DR

This paper introduces optimized Byzantine Fault Tolerance protocols for distributed SDN control planes, enhancing throughput, reducing response time, and lowering communication overhead while maintaining correctness and consistency.

## Contribution

It proposes new agreement-and-execution group-based BFT protocols and a state-hashing approach for causally ordered switch reconfigurations in SDN controllers.

## Key findings

- Decreased system response time compared to existing methods
- Reduced signaling overhead in the proposed protocols
- Validated effectiveness on realistic topologies and applications

## Abstract

Distributed Software Defined Networking (SDN) controllers aim to solve the issue of single-point-of-failure and improve the scalability of the control plane. Byzantine and faulty controllers, however, may enforce incorrect configurations and thus endanger the control plane correctness. Multiple Byzantine Fault Tolerance (BFT) approaches relying on Replicated State Machine (RSM) execution have been proposed in the past to cater for this issue. The scalability of such solutions is, however, limited. Additionally, the interplay between progressing the state of the distributed controllers and the consistency of the external reconfigurations of the forwarding devices has not been thoroughly investigated. In this work, we propose an agreement-and-execution group-based approach to increase the overall throughput of a BFT-enabled distributed SDN control plane. We adapt a proven sequencing-based BFT protocol, and introduce two optimized BFT protocols that preserve the uniform agreement, causality and liveness properties. A state-hashing approach which ensures causally ordered switch reconfigurations is proposed, that enables an opportunistic RSM execution without relying on strict sequencing. The proposed designs are implemented and validated for two realistic topologies, a path computation application and a set of KPIs: switch reconfiguration (response) time, signaling overhead, and acceptance rates. We show a clear decrease in the system response time and communication overhead with the proposed models, compared to a state-of-the-art approach.