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Network functions virtualization and software-defined networking are two closely related technologies that often...
exist together -- but not always. Broadly, NFV and SDN both use virtualization and automation to facilitate the creation of more nimble, responsive networks, but the two technologies differ in their specific goals and execution.
While both SDN and NFV abstract network intelligence from physical hardware, SDN typically involves doing so across the network as a whole, while NFV deals with virtualizing individual network services.
The SDN and NFV concepts emerged around 2011 and 2012, respectively, with each one spurring industry interest in the other. They both experienced an incredible amount of hype about their potential to revolutionize network agility and management, but neither technology ever truly met expectations in the networking industry.
Features of SDN
SDN separates a network's control plane from its data plane, logically centralizing intelligence to enable high-level network programmability. Forwarding still occurs at the device level, but decision-making happens within a software-based central controller.
While traditional network infrastructure is relatively static, programmable networks can better and more efficiently adapt to the constantly changing needs of current IT environments. SDN lets network managers rapidly deploy, provision, configure and manage network resources as necessary -- via automated scripts or other related tools -- without manually changing each individual device.
A software-defined network can be considered a series of network objects -- such as switches, routers and firewalls -- that are deployed in a highly automated manner with centralized control. The automation may be achieved by using commercial or open source tools -- like SDN controllers and OpenFlow -- based on the administrator's requirements. A full software-defined network may cover only relatively straightforward networking requirements, such as virtual LAN and interface provisioning.
Features of NFV
Similarly but distinctly, NFV is the process of moving services, like load balancing, firewalls and intrusion prevention systems, away from dedicated hardware into a virtualized environment. This is, of course, part of a wider movement toward the virtualization of applications and services.
Functions like caching and content control can easily be migrated to a virtualized environment but won't necessarily provide any significant reduction in operating costs until some intelligence is introduced. This is because a straight physical-to-virtual migration, from an operational perspective, achieves little beyond the initial reduction in power and rack space consumption.
Until some dynamic intelligence is introduced with an SDN technology, NFV network deployments inherit many of the same constraints as traditional hardware appliance deployments, such as static, administrator-defined and managed policies.
Virtual application delivery controllers (ADCs) provide a good example of these NFV limitations. With careful configuration, it is possible to react to the network state and spin up or down application servers as demands rise and fall. Traditional hardware deployments have been able to do this for a while. However, the configuration is static; it doesn't cater to the scenario where the ADC itself becomes overloaded or an additional application needs to be brought into production quickly.
Enterprises never found a compelling use case for NFV, but many service providers and operators deployed NFV within their private infrastructures to better meet customer demands for service delivery. Another NFV complication developed around a lack of industry standards for NFV management and orchestration.
SDN vs. NFV: Better together
With SDN features driving an NFV network, several useful things start to happen. SDN creates a virtual overlay that helps provision and manage the virtual network functions with NFV. SDN also helps manage traffic loads more efficiently, so the network can react when things need to change at micro and macro levels.
In the case of virtual ADCs, an additional instance can be provisioned in a cluster of virtual ADCs as the load increases, and production applications can easily be cloned and redeployed in a development environment. The potential for SDN and NFV is endless.
It's perfectly possible to have NFV without the inclusion of a full-blown software-defined network. Still, NFV and SDN are often deployed together, and a software-defined network that drives NFV is a powerful combination. Ultimately, business needs should determine the implementation of either or both technologies.
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