The Role of Inter-Controller Traffic for Placement of Distributed SDN Controllers

TL;DR

This paper analyzes how inter-controller traffic affects the placement of distributed SDN controllers, proposing optimization methods to improve network responsiveness and reliability in large-scale SDN deployments.

Contribution

It introduces a quantitative framework for optimizing controller placement considering both control traffic types and validates it with real SDWAN data.

Findings

Controller placement significantly impacts switch reaction time.

Inter-controller traffic influences network delay and performance.

A novel evolutionary algorithm effectively finds optimal placement tradeoffs.

Abstract

We consider a distributed Software Defined Networking (SDN) architecture adopting a cluster of multiple controllers to improve network performance and reliability. Besides the Openflow control traffic exchanged between controllers and switches, we focus on the control traffic exchanged among the controllers in the cluster, needed to run coordination and consensus algorithms to keep the controllers synchronized. We estimate the effect of the inter-controller communications on the reaction time perceived by the switches depending on the data-ownership model adopted in the cluster. The model is accurately validated in an operational Software Defined WAN (SDWAN). We advocate a careful placement of the controllers, that should take into account both the above kinds of control traffic. We evaluate, for some real ISP network topologies, the delay tradeoffs for the controllers placement problem and we propose a novel evolutionary algorithm to find the corresponding Pareto frontier. Our work provides novel quantitative tools to optimize the planning and the design of the network supporting the control plane of SDN networks, especially when the network is very large and in-band control plane is adopted. We also show that for operational distributed controllers (e.g. OpenDaylight and ONOS), the location of the controller which acts as a leader in the consensus algorithm has a strong impact on the reactivity perceived by switches.