SDN Fabric, Underlay, Overlay Networks and Architectures

This tutorial explains software-defined networking and its components, such as the underlay network, the overlay network, and the SDN fabric.

There are two types of networking: traditional and controller-based. In conventional networking, you individually configure and manage each network device. For example, if you have ten routers in your network, you must configure and manage them separately.

In Controller-based networking, you configure and manage devices from a central location. You use controller software or an SDN device that automates configuration changes on the network and manages their deployment to multiple devices simultaneously. Since it uses software to apply and manage configuration changes to devices on the network, it is also known as Software-Defined Networking (SDN).

An SDN controller centralizes the control of the networking devices. Based on the network's requirements, you can configure the level of control. For example, you can configure the controller to perform all control plane functions, replacing the devices' distributed control plane. Alternatively, you can configure it to monitor the ongoing work of the distributed data, control, and management planes on the network devices without altering their operation. There are three ways to implement an SDN.

• You can install it as software on a server available on the network.
• You can use an SDN device. An SDN device contains the controller.
• You can install it on the cloud as a remote controller.

No matter how you install or implement the controller device or software, it uses various tools such as Puppet, Chef, and Ansible to manage and automate changes on the network. SDN provides a graphical overview of the network. It allows you to manage a network device directly from the GUI screen. To operate a device, you select it on the SDN screen and change its settings. The SDN then applies those changes to that device. With SDN, you do not need to visit devices to manage them physically. You can manage them directly from the SDN screen.

SDN Architecture

Unlike traditional networking, which uses a flat architecture, SDN uses a layered architecture. It divides the network into two layers: underlay and overlay.

Underlay Network

It is the bottom layer. It contains all regular network components, such as routers and switches. To build an SDN environment, you must first configure appropriate protocols and features on all network devices to enable access and network communication. It means you need to configure IP addresses on all interfaces and allow routing between all routers. You must use an open standard protocol such as OSPF, BGP, or IS-IS as the routing protocol.

Overlay network

It is the upper layer. It builds on top of the underlay network. It includes the virtual networks created on top of the underlay network that use virtual technologies such as VRF (virtual routing and forwarding), MPLS VPN (multiprotocol label switching virtual private network), and VXLAN (Virtual Extensible LAN).

Differences between underlay and overlay networks

The following table compares the underlay and overlay networks and lists their differences.

SDN Fabric

The SDN fabric includes all the components that make up the SDN network. It consists of the physical network devices that form the underlay network and are controlled by the SDN controller. In other words, it is a combination of both underlay and overlay networks.

Conclusion

Software-Defined Networking (SDN) represents a significant shift from traditional networking paradigms by enabling centralized management and automation of network devices. By utilizing a layered architecture that separates the underlay and overlay networks, SDN optimizes both physical and virtual networking environments. The underlay network consists of the core physical infrastructure, while the overlay network leverages virtual technologies to enhance flexibility and scalability. SDN streamlines network operations by allowing administrators to manage devices and configurations from a centralized controller, resulting in improved efficiency and reduced complexity. Additionally, tools like Puppet, Chef, and Ansible further enhance the automation processes, making it easier to deploy changes across multiple devices simultaneously. Overall, SDN offers a robust framework for modern network management, catering to the evolving needs of dynamic and agile network environments.