What is software-defined networking (SDN)

Software-defined networking (SDN) is an architecture that aims to make networks agile and flexible. The goal of SDN is to improve network control by enabling enterprises and service providers to respond quickly to changing business requirements.

In a software-defined network, a network engineer or administrator can shape traffic from a centralized control console without having to touch individual switches in the network. The centralized SDN controller directs the switches to deliver network services wherever they're needed, regardless of the specific connections between a server and devices.

This process is a move away from traditional network architecture, in which individual network devices make traffic decisions based on their configured routing tables.

SDN architecture

A typical representation of SDN architecture comprises three layers: the application layer, the control layer and the infrastructure layer.

The application layer, not surprisingly, contains the typical network applications or functions organizations use, which can include intrusion detection systems, load balancing or firewalls. Where a customary system would utilize a specific machine, for example, a firewall or burden balancer, a product characterized arrange replaces the apparatus with an application that utilizes the controller to oversee information plane conduct.

SDN engineering isolates the system into three recognizable layers, associated through northbound and southbound APIs.

The control layer speaks to the brought together SDN controller programming that goes about as the mind of the product characterized organize. This controller lives on a server and oversees arrangements and the progression of traffic all through the system.

The framework layer is comprised of the physical switches in the system.

These three layers communicate using respective northbound and southbound application programming interfaces (APIs). For example, applications talk to the controller through its northbound interface, while the controller and switches communicate using southbound interfaces, such as OpenFlow -- although other protocols exist.

There is currently no formal standard for the controller's northbound API to match OpenFlow as a general southbound interface. It is likely the OpenDaylight controller's northbound API may emerge as a de facto standard over time, given its broad vendor support.

How SDN works

SDN encompasses several types of technologies, including functional separation, network virtualization and automation through programmability.

Originally, SDN technology focused solely on separation of the network control plane from the data plane. While the control plane makes decisions about how packets should flow through the network, the data plane actually moves packets from place to place.

In a classic SDN scenario, a packet arrives at a network switch, and rules built into the switch's proprietary firmware tell the switch where to forward the packet. These packet-handling rules are sent to the switch from the centralized controller.

The switch -- also known as a data plane device -- queries the controller for guidance as needed, and it provides the controller with information about traffic it handles. The switch sends every packet going to the same destination along the same path and treats all the packets the exact same way.

Software-defined networking uses an operation mode that is sometimes called adaptive or dynamic, in which a switch issues a route request to a controller for a packet that does not have a specific route. This process is separate from adaptive routing, which issues route requests through routers and algorithms based on the network topology, not through a controller.

The virtualization aspect of SDN comes into play through a virtual overlay, which is a logically separate network on top of the physical network. Users can implement end-to-end overlays to abstract the underlying network and segment network traffic. This microsegmentation is especially useful for service providers and operators with Multi-tenant cloud environments and cloud services, as they can provision a separate virtual network with specific policies for each tenant.

Benefits of SDN

With SDN, an administrator can change any network switch's rules when necessary -- prioritizing, deprioritizing or even blocking specific types of packets with a granular level of control and security. This is especially helpful in a cloud computing multi-tenant architecture, because it enables the administrator to manage traffic loads in a flexible and more efficient manner. Basically, this empowers the head to utilize more affordable ware switches and have more authority over system traffic stream than any time in recent memory.

Different advantages of SDN are organize the board and start to finish perceivability. A system chairman need just arrangement with one brought together controller to circulate approaches to the associated switches, rather than designing various individual gadgets. This ability is additionally a security advantage in light of the fact that the controller can screen traffic and convey security arrangements. If the controller deems traffic suspicious, for example, it can reroute or drop the packets.

SDN likewise virtualizes equipment and administrations that were recently done by committed equipment, bringing about the promoted advantages of a diminished equipment impression and lower operational expenses.

Also, programming characterized organizing added to the rise of programming characterized wide zone arrange (SD-WAN) innovation. SD-WAN utilizes the virtual overlay part of SDN innovation, abstracting an association's availability joins all through its WAN and making a virtual system that can utilize whichever association the controller esteems fit to send traffic.

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