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SDN vs. NFV: What’s the difference?

SDN vs. NFV: What’s the difference?

Ed Tittel

by Ed Tittel

While both architectures use network abstraction, they do so differently. Lets dig into the differences between SDN and NFV technologies. 

While there has been much talk about the power of bringing virtualization to the network, confusion abounds about two different but related approaches: software-defined networking and network functions virtualization.

SDN vs. NFV: Similarities and differences

The core similarity between software-defined networking (SDN) and network functions virtualization (NFV) is that they both use network abstraction. SDN seeks to separate network control functions from network forwarding functions, while NFV seeks to abstract network forwarding and other networking functions from the hardware on which it runs. Thus, both depend heavily on virtualization to enable network design and infrastructure to be abstracted in software and then implemented by underlying software across hardware platforms and devices.

When SDN executes on an NFV infrastructure, SDN forwards data packets from one network device to another. At the same time, SDN's networking control functions for routing, policy definition and applications run in a virtual machine somewhere on the network. Thus, NFV provides basic networking functions, while SDN controls and orchestrates them for specific uses. SDN further allows configuration and behavior to be programmatically defined and modified.

SDN and NFV differ in how they separate functions and abstract resources. SDN abstracts physical networking resources –switches, routers and so on – and moves decision making to a virtual network control plane. In this approach, the control plane decides where to send traffic, while the hardware continues to direct and handle the traffic. NFV aims to virtualize all physical network resources beneath a hypervisor, which allows the network to grow without the addition of more devices.

While both SDN and NFV make networking architectures more flexible and dynamic, they perform different roles in defining those architectures and the infrastructure they support.

Inside SDN

SDN essentially defines the big-picture side of networking: the kinds of infrastructure desired, the services and applications they deliver, and the network policies that formulate and guide their delivery and use. This kind of functionality –  especially the associated rules and policies –  changes over time, sometimes rapidly. It also explains the emphasis on programmable network control and the use of SDN controllers with a purview over entire infrastructures.

The key ingredients of SDN include the following:

  • SDN delivers directly programmable network control: The ability to provision new network elements and devices, or to reconfigure existing ones, comes from a collection of programmable interfaces. This allows administrators to easily program networks either via scripting tools or third-party tools and consoles, all of which employ those programmable interfaces.
  • SDN is agile and responsive: SDN permits administrators to adjust network-wide traffic flow dynamically to meet fluctuating needs and demands.
  • Network intelligence is logically centralized through SDN controllers: Implemented in software, controllers maintain a coherent global view of the network. To applications and policy engines, SDN looks like a single, logical switch.
  • SDN provides programmable configuration: Network managers can configure, control, secure and tune network resources using automated SDN programs. Furthermore, networking professionals can create such programs themselves using standard, well-documented tools and interfaces.
  • SDN is standards-based and vendor-neutral: Using open standards, SDN streamlines network design and operation. Instructions originate from SDN controllers using standard protocols and interfaces, rather than relying on vendor-specific protocols, interfaces and devices.

Changing networking trends drive SDN adoption

Traditional hardware-based networks don’t mesh well with ever-changing computing and storage needs in campus environments, data centers and carrier/service provider environments. SDN provides a better fit in such situations, where numerous characteristics demand a more flexible and dynamic approach. These situations include the following:

  • Rapidly changing usage and varying traffic patterns are the norm. Applications that access geographically dispersed data and services go through both public and private clouds. They require flexible, dynamically adjustable traffic management and the ability to obtain bandwidth as needed.
  • IT is becoming a consumer commodity, where the bring-your-own-device (BYOD) trend requires networks to be flexible enough to accommodate whatever devices users bring with them. But networks must also be secure enough to protect data and assets as well as to meet compliance regulations and standards, such as the Health Insurance Portability and Accountability Act (HIPAA) and the Payment Card Industry Data Security Standard (PCI-DSS).
  • The proliferation of cloud services means that users require unfettered access to infrastructure, applications and IT resources --wherever and whenever needed.
  • With the rise in big data use for various business processes, there's an accompanying requirements for more storage, compute and bandwidth to handle data sets. If resources are adequate today, they will be constrained tomorrow.

Further, conventional networks impose limitations that hamper designers' efforts to keep up with the ever-changing landscape of users, resources, services and applications.

The first such limitation is posed by complexity and effort. Bolstering capacity or capability means adding and moving devices or crafting network-wide policy. The work involved is complex and time consuming, and requires manual access to individual devices and consoles. Change is a heavy burden.

Next, the established practice of oversubscribing to links means that scalability becomes a real challenge. This is exacerbated by the dynamic traffic patterns typical in virtualized networks, which vary widely depending on the kinds of workloads present as well as by usage and communication patterns.

Finally, conventional networks must adhere to the product cycles and proprietary interfaces typical in vendor-specific environments. Network operators will often be stymied in their attempts to tailor and customize their networks, especially programmatically.

Ultimately, SDN rests on the notion that network control can be divorced from network infrastructure and physical devices. By applying programming and automation to network control, network operators can define, manage and manipulate logical networks directly and dynamically.

NFV explored and explained

NFV, by contrast, is all about the network functions that must be performed at all levels and stages of a network – at the periphery, boundary and core – to accept, forward, shape and filter network traffic as it courses through any given infrastructure.

There are several important points about NFV to note:

  • NFV replaces network services provided by dedicated hardware with virtualized software. This means that network services, such as routers, firewalls, load balancers, XML processing and WAN optimization devices, can be replaced with software running on virtual machines. Virtualized network functions are under the control of a hypervisor, which is the role that SDN fulfills in such a scenario.
  • NFV helps save both capital expenditures (CAPEX) and operating expenses (OPEX). Network services that used to require specialized, dedicated hardware can run on standard commodity servers (such as ARM, x86 commodity hardware, and so forth), reducing costs. Because server capacity can be increased or reduced through software settings made on demand, it is no longer necessary to overprovision data or service centers to accommodate peak demand.

NFV is an industry initiative that originates from global telecom and industry players, including AT&T, BT (British Telecommunications), Deutsche Telekom and others. Today, NFV falls under the aegis of ETSI, the European Telecommunications Standards Institute, which seeks to define and maintain "globally applicable standards for information and telecommunications technologies." Current ETSI-NVF publications from the 2015-16 Release 2 version cover many topics, such as virtualized resources management, capacity management and Universal Modeling Language.

Where to next?

This is the first in a series of articles on SDN and NFV. The second will explore professional IT certifications that focus on or include substantial coverage of SDN and/or NFV topics. A third piece in this series will share educational resources to help interested IT professionals improve their understanding of SDN and NFV and develop skills in these important topic areas.

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Ed Tittel

Ed Tittel

Ed Tittel is a 30-plus year IT veteran who's worked as a developer, networking consultant, technical trainer, writer and expert witness. Perhaps best known for the Exam Cram series of IT cert prep books, Tittel has contributed to more than 100 titles on computing topics, including information security, Windows OSes and HTML.