[Paper Review] ZeroSDN: A Message Bus for Flexible and Light-weight Network Control Distribution in SDN

Frank Dürr, Thomas Kohler+2 more|arXiv (Cornell University)|Oct 14, 2016

Software-Defined Networks and 5G16 references4 citations

TL;DR

ZeroSDN proposes a micro-kernel-based, message bus–driven SDN controller architecture that decomposes control logic into lightweight, distributable controllets. By leveraging content-based publish/subscribe messaging, it enables flexible, low-overhead distribution of control logic—including execution directly on switches—achieving full decentralization without requiring external controllers.

ABSTRACT

Recent years have seen an evolution of SDN control plane architectures, starting from simple monolithic controllers, over modular monolithic controllers, to distributed controllers. We observe, however, that today's distributed controllers still exhibit inflexibility with respect to the distribution of control logic. Therefore, we propose a novel architecture of a distributed SDN controller in this paper, providing maximum flexibility with respect to distribution. Our architecture splits control logic into light-weight control modules, called controllets, based on a micro-kernel approach, reducing common controllet functionality to a bare minimum and factoring out all higher-level functionality. Light-weight controllets also allow for pushing control logic onto switches to minimize latency and communication overhead. Controllets are interconnected through a message bus supporting the publish/subscribe communication paradigm with specific extensions for content-based OpenFlow message filtering. Publish/subscribe allows for complete decoupling of controllets to further facilitate control plane distribution.

Motivation & Objective

• Address the inflexibility of existing distributed SDN controllers in distributing control logic across switches and controllers.
• Overcome the limitations of monolithic and modular monolithic controllers by enabling fine-grained, dynamic distribution of control functions.
• Decouple controllets from switches and each other to support both centralized and fully distributed control deployment.
• Minimize control logic overhead to allow execution of controllets directly on switches, reducing latency and communication costs.
• Provide a flexible, extensible architecture that supports both local caching and consistent global state access for scalable control plane operation.

Proposed method

• Decompose network control logic into minimal, lightweight control modules called controllets using a micro-kernel design.
• Connect controllets via a message bus that supports content-based publish/subscribe communication with topic hierarchy mapping.
• Implement content-based filtering on the message bus to allow fine-grained subscription to specific OpenFlow message types and attributes.
• Decouple controllets from switches and from each other through message-passing, enabling dynamic and flexible deployment across physical nodes.
• Support execution of controllets directly on Whitebox switches to enable fully distributed control without external controllers.
• Provide both local caches for low-latency access and integration with centralized, consistent storage for global state management.

Experimental results

Research questions

• RQ1 How can SDN control plane distribution be made maximally flexible to support deployment ranging from fully centralized to fully distributed?
• RQ2 What architectural principles enable lightweight, modular control logic that can be efficiently distributed and executed even on switches?
• RQ3 How can publish/subscribe messaging with content-based filtering support scalable and decoupled communication between distributed control components?
• RQ4 To what extent can control logic be offloaded to switches without sacrificing consistency or coordination?
• RQ5 What mechanisms enable seamless integration of local caches and consistent global state in a distributed control plane?

Key findings

• ZeroSDN enables full distribution of control logic by decomposing it into minimal controllets that can be deployed on switches or controllers.
• The message bus with content-based filtering allows fine-grained, efficient event propagation, reducing unnecessary message traffic.
• Controllets are extremely lightweight, enabling execution directly on switches and eliminating dependency on external controllers.
• The decoupling of controllets from switches and from each other allows for dynamic, flexible, and failure-resilient control plane deployment.
• The architecture supports both local caching for performance and consistent global state access, enabling scalable and robust control plane operation.
• The approach eliminates the need for complex switch migration protocols by decoupling switches from specific controller instances.