How SDN Bridges Networks and Cloud Platforms: An In‑Depth Look

In recent years, buzzwords such as cloud computing, IoT, big data, SDN, and blockchain have created confusion, especially for network engineers who focus on SDN and cloud computing. This article clarifies how these two domains intersect.

Cloud Computing Overview

Cloud computing comprises three service models: IaaS (Infrastructure as a Service), PaaS (Platform as a Service), and SaaS (Software as a Service). The discussion concentrates on the IaaS layer, which provides shared resources—network, server, storage, compute, applications, and services—through a powerful platform that enforces standards and offers unified management.

Two layers manage these resources:

Cloud Platform (CP) : Offers open APIs and management software for users to request, manage, and consume cloud resources.

Cloud Management Platform (CMP) : Sits above CP and enables roles such as R&D, IT, and data analysis to orchestrate multiple cloud infrastructures via standardized commands.

SDN Overview

Software‑Defined Networking (SDN) decouples control and forwarding, provides open APIs, and enables centralized management. Compared with traditional networks, SDN reduces development cycles, network complexity, deployment time, operational overhead, and improves compatibility across heterogeneous devices.

Real‑world adoption faces challenges: legacy network constraints, varying user acceptance, and incomplete protocol maturity. Consequently, the industry adopts a “broad‑sense SDN” approach, gradually introducing SDN control while minimizing impact on existing networks.

Integrating SDN with Cloud Platforms

Effective cloud operation requires coordinated network, storage, compute, and service resources. Because devices use diverse protocols, a unified management layer is essential. The SDN controller serves as this assistant, exposing standardized, open APIs to the cloud platform, allowing seamless scheduling of both physical and virtual network devices.

Similarly, storage, compute, and security resources each have dedicated controllers that expose open APIs, reducing the cloud platform’s burden and letting it focus on policy definition.

OpenStack Core Services

OpenStack is the dominant open‑source cloud platform. Its six core services are:

Compute (Nova) : Manages virtual machines.

Storage : Object storage (Swift) and block storage (Cinder).

Networking (Neutron) : Provides pluggable, API‑driven network and IP management.

Identity (Keystone) , Image (Glance) , and Dashboard : Offer authentication, image handling, and a unified web UI.

Neutron is the component most closely related to SDN, handling all interactions with physical networks.

OpenDaylight (ODL) Controller

OpenDaylight is a widely adopted open‑source SDN controller in enterprise environments. The RG‑ONC controller from Ruijie Networks is built on ODL and consists of three layers:

Infrastructure Layer : Traditional and SDN network devices (switches, routers, firewalls, gateways) in both physical and virtual forms.

Controller Layer : Provides north‑bound APIs for applications and south‑bound APIs for network devices, along with a web UI. Key metrics are independence, usability, and scalability.

Application Layer : Includes cloud platforms, network management systems, and custom applications that consume the north‑bound APIs.

SDN‑OpenStack Integration Model

The integration relies on the Networking‑odl plugin, which implements two components:

OpenDaylight Mechanism Driver : Acts as a REST proxy, translating Neutron ML2 calls into OpenDaylight NB REST service requests.

OpenDaylight L3 Router Plugin : Extends OpenStack’s L3 router functionality (router, external gateway mode, extra routes, DVR, L3‑HA) by forwarding calls to OpenDaylight via REST.

When the plugin is installed on OpenStack, all networking operations—creating networks, subnets, routers, binding subnets, and launching instances—are processed through the SDN controller, achieving unified, programmable network management.

By adhering to open standards, this integration maintains compatibility across different cloud platforms and SDN controllers, allowing vendors to add proprietary features without breaking the interface.