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Software-defined network (SDN) is an architecture desig ned to make the network agile and flexible. SDN’s goal is to improve network control by enabling businesses and service providers to respond quickly to changing business needs.
In a software-defined network, network engineers or administrators can adjust traffic from the central console without touching the individual switches in the system. a centralized SDN controller directs the button to provide network services wherever needed, independent of the specific connection between the server and the device.
This process is different from traditional network architecture. In the conventional network architecture, a single network device makes traffic decisions according to its configured routing table.
SDN Architecture
A typical representation of SDN architecture consists of three layers: application layer, control layer, and infrastructure layer.
Not surprisingly, the application layer contains typical network applications or functions used by the organization, including intrusion detection systems, load balancing, or firewalls. Where traditional networks will use dedicated devices (e.g., firewalls or load balancers), software-defined networks replace appliances with applications that use controllers to manage data plane behavior.
A control layer represents a centralized SDN controller software that acts as the brain of a software-defined network. The controller resides on the server and manages policies and traffic throughout the system.
The infrastructure layer consists of physical switches in the network.
These three layers use their respective north and south application programming interfaces (API) for communication. For example, despite other protocols, applications communicate with controllers through their northward interfaces, while controllers and switches use southbound interfaces (e.g., OpenFlow) communicate.
There is no formal standard for the controller’s northward API to match the OpenFlow as a general southbound interface. The northward API of the OpenDaylight controller may gradually become a de facto standard given its extensive supplier support.
How SDN Works
SDN contains a variety of technologies, including feature separation, network virtualization, and automation through programmability
Initially, SDN technology-focused only on separating the network control plane from the data plane. Although the control plane determines how packets should flow through the network, the data plane moves boxes from one place to another.
In the classic SDN scenario, packets arrive at the network switch, and the built-in rules in the switch proprietary firmware tell the switch where to forward the packets. These packet processing rules are sent from the central controller to the button.
A switch (also known as a data plane device) queries the controller for guidance as needed and provides the controller with information about the flow it processes. The switch will send each packet along the same path to the same destination and treat all boxes in the same way.
Software-defined networks sometimes use adaptive or dynamic operating modes, which switches issue routing requests to controllers for packets without specific routes. This process is separate from adaptive routing, routed through routers and network topology-based algorithms rather than through controllers.
SDN virtualization works through a virtual overlay, a logically independent network on a physical system.
Users can achieve end-to-end coverage to abstract the underlying network and segment network traffic. This fine-tuning is particularly useful for service providers and operators with multi-tenant cloud environments and cloud services. They can provide each tenant with a separate virtual network with specific policies.
Benefits of SDN
An administrator can change any network switch’s rules with SDN 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 flexibly and more efficiently. Essentially, this allows the administrator to use less expensive commodity switches and have more control over network traffic flow than ever before.
Other benefits of SDN are network management and end-to-end visibility. The network administrator only needs to process a centralized controller to assign the policy to the connected switch without configuring multiple separate devices. This feature is also a security advantage because the controller can monitor traffic and deploy security policies. For example, if the controller considers traffic suspicious, it can reroute or discard packets.
SDN also virtualized hardware and services previously performed by dedicated hardware, bringing the bragging benefits: reduced hardware footprint and reduced operating costs.
Furthermore, software-defined networks contribute to the emergence of software-defined WAN (SD-WAN) technologies. SD-WAN uses the virtual coverage aspect of SDN technology to abstract the organization’s connection links throughout the WAN and creates a virtual network that can send traffic using any connections that the controller thinks fit.
Challenges with SDN
For SDN technology, security is both good and problematic. A centralized SDN controller presents a single point of failure, proving harmful to the network if the attacker is the target.
Ironically, another challenge for SDN is that there is no established definition of a “software-defined network” in the network industry. different vendors offer various approaches to SDN, from hardware-centric models and virtualization platforms to hyperfusion network design and controller-free processes.
Several network plans are often mistaken for SDN, including white-box networks, network decomposition, network automation, and programmable networks.
Although SDN can benefit and cooperate with these technologies and processes, it is still an independent technology.
SDN technology was hyped when it was introduced with the OpenFlow agreement in 2011. Since then, adoption has been relatively slow, especially in enterprises
with smaller networks and fewer resources. Furthermore, many enterprises see the cost of SDN deployment as a disincentive.
The leading adopters of the SDN include service providers, network operators, telecommunications and operators, and large companies such as Facebook and Google, all of which have the resources to solve and contribute to emerging technologies.
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SDN use cases
Some use cases for SDN include:
DevOps: An approach based on software-defined networking can facilitate DevOps by automating app updates and deployments, including automating IT infrastructure components as the DevOps apps and platforms are deployed.
Campus networks: Campus networks can be challenging to manage, especially with the ongoing need to unify Wi-Fi and Ethernet networks. SDN controllers can benefit campus networks by offering centralized management and automation, improved security, and application-level service quality across the network.
Service provider networks: SDN helps service providers simplify and automate their networks’ provisioning for end-to-end network and service management and control.
Datacenter security: SDN supports more targeted protection and simplifies firewall administration. Generally, an enterprise depends on a traditional perimeter firewall to secure its entire datacenter. However, a company can create a distributed firewall system by adding virtual firewalls to protect the virtual machines. This extra layer of firewall security helps prevent a breach in one virtual machine from jumping to another. Also, SDN centralized control and automation allow the admin to view, modify, and control network activity to reduce the risk of a breach, to begin with.
The Impact of SDN
A software-defined network has a significant impact on the management of IT infrastructure and network design. The maturity of SDN technology changes the composition of network infrastructure. It reverses the IT view of its role because IT management has invested a lot of energy in the decision-making process and redefined the entire IT infrastructure.
SDN architectures can typically use open protocols (e.g. OpenFlow) to make network control programmable.
Therefore, enterprises can apply globally conscious software control to their network edges to access network switches and routers, rather than closed proprietary firmware that is usually used to configure, manage, protect and optimize network resources.
Although SDN is deployed in every industry, its impact is most substantial in technology-related areas and financial services.
SDN has had an impact on the way telecom companies operate. Verizon, for example, uses SDN to combine all its existing service edge routers for Ethernet and IP-based services into one platform.
The goal is to simplify the edge architecture so that Verizon can improve operational efficiency and flexibility to support new features and services. SDN will help Verizon improve network management and ultimately provide better service to their customers.
Success in financial services depends on connectivity to many transaction participants, low latency, and highly secure network infrastructure to power global financial markets.
Almost all financial markets participants rely on traditional networks, which are unpredictable, difficult to manage, slow to deliver, and have significant security vulnerabilities. But with SDN technology, organizations in the financial services sector can build predictive networks to enable more efficient financial transactions applications.
SDN and SD-WAN
SD-WAN is a technology that uses the SDN concept to distribute network traffic across the wide-area network (WAN), which can automatically determine the most effective method of commuting traffic to and from branches and data center sites.
SDN and SD-WAN have similarities. For example, they both separate the control plane from the data plane and support the implementation of other virtual network functions.
Nevertheless, although SDN mainly focuses on internal operations within the lan, SD-WAN route the application to the WAN to connect the organization’s geographically dispersed locations.
Other differences include:
The customer and SD-WAN can program SDN by the supplier.
SDN enabled through network function virtualization (NFV) in closed systems. On the other hand, SD-WAN provides application routing that runs on SD-WAN devices or can be virtualized.
SD-WAN use application-based routing systems on consumer-level broadband Internet. This can provide better quality performance and lower cost per megabyte than multi-protocol label switching (MPLS) that is critical to SDN.
SDN and SD-WAN are two different technologies designed to achieve other business objectives. Typically, small and medium-sized enterprises (SMB) use SD-WAN. In their centralized locations, while large companies want to establish interconnections between their headquarters and non-local sites.
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