The static architecture of traditional networks no longer meets the dynamic computing and storage needs of modern data centers.
By decoupling the network control plane from the data plane, software-defined networking (SDN) makes networks more open and interoperable, leading to lower costs, increased flexibility and control, plus greater innovation.
Instead of requiring data center managers to add extra applications, hardware and floor space to meet spiraling bandwidth and data capacity needs, SDN uses cost-effective virtualization to increase network efficiency. Consequently, the SDN approach can also help reduce operating and capital expenses (OPEX and CAPEX) as well as power usage, and improve operational and support efficiencies.
In addition, SDN can give network administrators greater control over their infrastructure, allowing extensive customization and optimization while trimming overall capital and operational costs. SDN also enables adopters in many service-oriented fields to create new revenue opportunities at an accelerated pace through the development of softwarebased applications — as the PC, mobile and web industries have been doing successfully for many years. SDN can also optimize the performance of many applications running on a network.
In fact, the growing complexity of traditional networks has created a giant roadblock that seriously hinders on-time network service delivery and quality. Enhanced quality of service (QoS) for latency-sensitive applications such as voice and video is yet another benefit provided by SDN’s open and automated approach.
SDN’s open and programmable application programming interfaces (APIs) for policy-based management and security allow organizations to automate formerly tedious and timeconsuming manual configurations, reducing the workloads of IT team members. Rather than requiring an IT staff member to manually configure each hardware component, SDN allows data centers to roll out network configurations and updates simply by sending out software updates.
Multiple SDN models and standards are evolving in different areas. Yet the technology is primed for widespread adoption and network dominance. SDN adopters can feel confident that the technology will always be based on open, interoperable multivendor ecosystems embracing either key open-source technologies or standardized protocols.
Major SDN Delivery Models
Any organization considering a move to SDN should be aware of the two main delivery models: imperative and declarative.
• Imperative SDN: A centralized controller (typically a clustered set of controllers) functions as the network’s “brain” in the imperative SDN model, with a protocol such as OpenFlow explicitly telling network switches precisely what to do and how to do it.
• Declarative SDN: In this model, the intelligence is distributed out to the network fabric. While policy is centralized, policy enforcement isn’t. A central controller is used to pass policy and configuration commands to network devices, with the infrastructure responding dynamically to applications’ needs. Cisco Application Centric Infrastructure (ACI) and the OpFlex protocol are used to implement declarative SDN.
The discussion about which SDN model provides the best approach is ongoing. Imperative proponents maintain that their model enables a high degree of network flexibility, because the software that governs the model can be created by both organizations and external vendors in everyday software environments. Imperative advocates also note that their model can provide a standardized way of conveying flow-table information to network devices, which encourages the formation of an open and active vendor market.
Imperative backers note that their model also promotes rapid service introduction via customization, because adopters can implement the features they need in software they control instead of waiting for a vendor to offer a specific capability.
Declarative model supporters counter that their approach separates application, operation and infrastructure requirements, allowing each to be specified independently. This separation can accelerate application deployment by allowing a system, rather than an administrator, to unite these requirements.
Another benefit is that systems based on the declarative model can achieve high performance at scale with strong resiliency by moving complexity to edge devices, which do most of the processing. Additionally, declarative systems, which allow policies to be specified in abstract terms, tend to be highly interoperable. Multiple vendors can support the same policy without the need to offer identical hardware configurations or software versions.
Software-Defined Network Overlay
Another point to consider when planning an SDN deployment is the use of a network overlay, which is a popular method for implementing an SDN architecture. An overlay is an SDN deployment approach that creates a logically separate network to run on top of the existing infrastructure.
Overlay networks, incorporating the ability to combine network resources by dividing available bandwidth into channels and then assigning each channel to a specific device or service in real time, represent a type of network virtualization. An overlay network separates the virtual network configuration and topologies from the physical networks lying underneath. The virtual network handles most of the higher level policy, allowing the underlying physical network to focus on delivering packets to their destination.
Deploying a software-defined network overlay allows an organization to reconfigure and upgrade its physical network as needed without affecting the virtual topology. The virtual network also enhances efficiency and productivity by allowing tasks typically performed by a network administrator to be handled seamlessly and automatically.
Learn more about the benefits of SDN by downloading the white paper, "The Future of Networking Arrives."