What Is Software-Defined Networking? 
Find out what software-defined networking (SDN) is, how it differs from traditional networks and network management, and why organizations are adopting this approach.
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What is SDN? 

SDN is an approach to networking that uses software controllers that can be driven by application programming interfaces (APIs) to communicate with hardware infrastructure to direct network traffic. Using software, it creates and operates a series of virtual overlay networks that work in conjunction with a physical underlay network. SDNs offer the potential to deliver application environments as code and minimize the hands-on time needed for managing the network.

Why use SDN? 

Companies today are looking to SDN to bring the benefits of the cloud to network deployment and management. With network virtualization, organizations can open the door to greater efficiency through new tools and technology, such as Software-as-a-Service (SaaS), Infrastructure-as-a-Service (IaaS) and other cloud computing services, as well as integrate via APIs with their software-defined network.

SDN also increases visibility and flexibility. In a traditional environment, a router or switch—whether in the cloud or physically in the data center—is only aware of the status of network devices next to it. SDN centralizes this information so that organizations can view and control the entire network and devices. Organizations can also segment different virtual networks within a single physical network or connect different physical networks to create a single virtual network, offering a high degree of flexibility. 

Simply put, companies are using SDN because it’s a way to efficiently control traffic and scale as needed.

How SDN works 

To better understand how SDN works, it helps to define the basic components that create the network ecosystem. The components used to build a software-defined network may or may not be located in the same physical area. These include:

·         Applications – Tasked with relaying information about the network or requests for specific resource availability or allocation.

·         SDN controllers – Handle communication with the apps to determine the destination of data packets. The controllers are the load balancers within SDN.

·         Networking devices – Receive instructions from the controllers regarding how to route the packets. 

·         Open-source technologies – Programmable networking protocols, such as OpenFlow, direct traffic among network devices in an SDN network. The Open Networking Foundation (ONF) helped to standardize the OpenFlow protocol and other open source SDN technologies. 

By combining these components, organizations get a simpler, centralized way to manage networks. SDN strips away the routing and packet forwarding functions, known as the control plane, from the data plane, or underlying infrastructure. SDN then implements controllers, considered the brain of the SDN network, and layers them above the network hardware in the cloud or on-premises. This lets teams use policy-based management—a kind of automation—to manage network control directly. 

SDN controllers tell switches where to send packets. In some cases, virtual switches that have been embedded in software or the hardware will replace the physical switches. This consolidates their functions into a single, intelligent switch that can check data packets and their virtual machine destinations to ensure there are no issues before moving packets along.

Virtualization and software-defined networking 

The term “virtual network” is sometimes erroneously used synonymously with the term SDN. These two concepts are distinctly different, but they do work well together.

Network functions virtualization (NFV) segments one or many logical, or virtual, networks within a single physical network. NFV can also connect devices on different networks to create a single virtual network, often including virtual machines.

SDN works well with NFV. It assists NFV by refining the process of controlling data packet routing through a centralized server, improving visibility and control.

Types of SDN 

There are four primary types of software-defined networking (SDN):

·         Open SDN – Open protocols are used to control the virtual and physical devices responsible for routing the data packets.

·         API SDN – Through programming interfaces, often called southbound APIs, organizations control the flow of data to and from each device.

·         Overlay Model SDN – It creates a virtual network above existing hardware, providing tunnels containing channels to data centers. This model then allocates bandwidth in each channel and assigns devices to each channel. 

·         Hybrid Model SDN – By combining SDN and traditional networking, the hybrid model assigns the optimal protocol for each type of traffic. Hybrid SDN is often used as an incremental approach to SDN.

Benefits of SDN 

SDN architecture comes with many advantages, largely due to the centralization of network control and management. Some of the benefits include:

·         Ease of network control – Separating the packet forwarding functions from the data plane enables direct programming and simpler network control. This could include configuring network services in real time, such as Ethernet or firewalls, or quickly allocating virtual network resources to change the network infrastructure through one centralized location.

·         Agility – Because SDN enables dynamic load balancing to manage the traffic flow as need and usage fluctuates, it reduces latency, increasing the efficiency of the network.

·         Flexibility – With a software-based control layer, network operators have more flexibility to control the network, change configuration settings, provision resources, and increase network capacity. 

·         Greater control over network security – SDN lets network administrators set policies from one central location to determine access control and security measures across the network by workload type or by network segments. You can also use micro-segmentation to reduce complexity and establish consistency across any network architecture—whether public cloud, private cloud, hybrid cloud or multicloud.

·         Simplified network design and operation – Administrators can use a single protocol to communicate with a wide range of hardware devices through a central controller. It also offers more flexibility in choosing networking equipment, since organizations often prefer to use open controllers rather than vendor-specific devices and protocols.

·         Modernizing telecommunications – SDN technology combined with virtual machines and virtualization of networks lets service providers provide distinct network separation and control to customers. This helps service providers improve their scalability and provide bandwidth on demand to customers who need greater flexibility and have variable bandwidth usage.

The risks of software-defined networking 

SDN solutions come with significant benefits but can pose a risk if not implemented correctly. The controller is critical in maintaining a secure network. It is centralized and, therefore, a potential single point of failure. This potential vulnerability can be mitigated by implementing controller redundancy on the network with automatic failover. This may be costly but is no different from creating redundancy in other areas of the network to ensure business continuity.

SD-WAN advances cloud implementation 

Service providers and organizations alike can benefit from a software-defined wide area network, or SD-WAN. A traditional WAN (wide-area network) is used to connect users to applications hosted on an organization’s servers in a data center. Typically, multiprotocol label switching (MPLS) circuits were used to route traffic along the shortest path, ensuring reliability. 

As an alternative, an SD-WAN is programmatically configured and provides a centralized management function for any cloud, on-premises or hybrid network topology in a wide area network. SD-WAN can not only handle massive amounts of traffic but also multiple types of connectivity, including SDN, virtual private networks, MPLS and others.

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