What is software-defined networking (SDN)?

Network World | Jun 25, 2017

A graphical look at the technology behind software-defined networking.

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The software defined networking (SDN) market started about five years ago and was heralded as the next great thing in networking. Now, SDN has evolved from a narrow use case to being applied across many different networking use cases.
About five years ago software defined networking, or SDN, was pegged as the next big thing in the networking industry. So where are we now?
Researchers at Stanford are credited with creating the idea of bringing the tenets of virtualization to networking, and thus software defined networking was born.
Traditional networking uses integrated hardware and software to direct traffic across a series of routers and switches.
The original use case for SDN was to virtualize the network by separating the control plane that manages the network from the data plane where traffic flows. There is a smart controller running specialized software that manages all network traffic in a data center, and a series of routers and switches that forward packets of traffic.
Virtualizing the network comes with advantages: Networks can be spun up and down dynamically, they can be fine-tuned for specific application use cases, and security policies can be installed on each individual network.
Today, the SDN market has evolved, and it’s breaking out of the data center. SDN is being used in the Wide Area Network to control how enterprises connect to their branch offices. This use case called SD-WAN uses software to aggregate multiple types of network connections, such as broadband, MPLS or wireless to create strong and cost effective connections.
SDN has been applied to security using what is called microsegmentation, which is the idea of segmenting network traffic for security purposes. Certain networks can be ultra-secure and carry sensitive data. Other networks can be public facing. So, if a hacker gets into the data center, they are restricted to only a specific part of the network, limiting their impact.
SDN is also used in an area called Network Function Virtualization, or NFV. This is the idea of replacing specialized hardware like firewalls and load balancers with software running on off-the-shelf server hardware.
Some vendors are using SDN to connect data centers to public cloud providers, creating a hybrid cloud network that includes microsegmentation or dynamic scaling abilities. Other SDNs could be used to help manage the deluge of traffic from the Internet of Things, segmenting network traffic and helping to organize the data.
SDN has evolved from a specific use case to being applied to many different areas of networking, both within the data center, out to the cloud and in the new world of IoT. As software is used to control the network, it becomes more agile, easier to manage and it’s ready to adapt to whatever use cases emerge in the future.