Software Defined Networking
What is SDN?
Software-defined networking (SDN) is an umbrella term encompassing several kinds of network technology aimed at making the network as agile and flexible as the virtualized server and storage infrastructure of the modern data center.
The goal of SDN is to allow network engineers and administrators to respond quickly to changing business requirements. In a software-defined network, a network administrator can shape traffic from a centralized control console without having to touch individual switches, and can deliver services to wherever they are needed in the network, without regard to what specific devices a server or other device is connected to. The key technologies are functional separation, network virtualization and automation through programmability.
Originally, SDN focused solely on separation of the control plane of the network, which makes decisions about how packets should flow through the network from the data plane of the network, which actually moves packets from place to place. When a packet arrives at a switch in network, rules built into the switch’s proprietary firmware tell the switch where to forward the packet. The switch sends every packet going to the same destination along the same path, and treats all the packets the exact same way. In a classic SDN scenario, rules for packet handling are sent to the switch from a controller, an application running on a server somewhere, and switches (aka data plane devices) query the controller for guidance as needed, and provide it with information about traffic they are handling. Controllers and switches communicate via a controller’s “south bound” interface, usually OpenFlow, although other protocols exist.
Where a traditional network would use a specialized appliance such as a firewall or load balancer, an SDN deploys an application that uses the controller to manage data plane behavior. Applications talk to the controller via its “north-bound” interface. As of the end of 2014, there is no formal standard for the application interface of the controller to match OpenFlow as a general south-bound interface. The OpenDaylight controller’s northbound API may emerge as a defacto standard over time, given its broad vendor support.
The administrator can change any network switch’s rules when necessary — prioritizing, de-prioritizing or even blocking specific types of packets with a very granular level of control. This is especially helpful in a cloud computing multi-tenant architecture, because it allows the administrator to manage traffic loads in a flexible and more efficient manner. Essentially, this allows the administrator to use less expensive commodity switches and have more control over network traffic flow than ever before.
Benefits of SDN
Programmable networks: Historically, your network was only as good as the hardware that controlled it. SDN changes all that and provides easy customizations, even down to the individual customer level. With hardware decoupled from software, you can introduce innovative, differentiated new services quickly—something previously unimagined with the constraints of closed and proprietary platforms.
Intelligence and control centralized: Bandwidth management, restoration, security, and policies have been a thorn in the side of every network operator. Now, with those functions centrally controlled by an SDN controller that is highly intelligent and optimized, you now have a holistic view of the network. That is an asset to your operations, not a legacy liability. With network control centralized, your network resources can be controlled and managed in a coordinated way to delivery services end to end. And devices now operate with awareness of the conditions of the network overall.
Network interaction via APIs: Your static physical hardware and network connections are a thing of the past with SDN. Services and applications are no longer tied to network hardware and connections. Instead, your applications connect over the network infrastructure flexibly, with the use of APIs, between OSS/BSS, orchestration, and assurance systems.
Vendor-neutral architectures: SDN enables an open approach that is vendor-neutral and supports a large assortment of applications. Cloud orchestration, SaaS, and business-critical networked apps are just a few of the possibilities SDN enables. With SDN, intelligent network services and applications run in a common IT environment that can control the hardware and associated technologies of countless vendors.
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