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What is the difference between SDN and NFV?

To help make sense of SDN and NFV differences, SDN expert Glen Kemp compares the two technologies, and discusses how they affect each other and whether they can work together.

What is the difference between SDN and NFV?

Network functions virtualization and software-defined networking are two closely related technologies that often exist together, but not always. NFV and SDN are both moves toward network virtualization and automation, but the two technologies have different goals.

An SDN can be considered a series of network objects -- such as switches, routers and firewalls -- that are deployed in a highly automated manner. 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 VLAN and interface provisioning.

In many cases, SDN will also be linked to server virtualization, providing the glue that sticks virtual networks together. This may involve NFV, but not necessarily. 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, 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.

A good example is virtualized application delivery controllers (ADCs). 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, and the configuration is very 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.

SDN fabric with NFV devices
How SDN and NFV work together

How SDN and NFV work together

With SDN features driving an NFV network, several useful things start to happen. The virtual overlay created by SDN 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. An additional instance can be provisioned in a cluster of virtualized 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.

So, 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 very powerful combination.

Neither NFV nor SDN are turnkey services in early 2014 -- a great deal of integration and policy design still need to happen. Standards work for both SDN and NFV network architectures is still ongoing, and the two technologies need more proven deployments. But while the harness is not entirely in place, NFV and SDN can become a reality for many enterprises. That said, the tools are rapidly evolving, and many vendors are bringing technologies to market that support SDN or NFV deployments. Ultimately, the implementation of either or both technologies will be driven by the business needs.

See also: SDN and NFV network components are changing the networking industry, so students should be getting SDN and NFV training in school.

Next Steps

Two factors affecting the deployments of NFV and SDN

Three technologies to enhance the benefits of NFV and SDN

Making NFV and SDN proof-of-concept trials more meaningful

This was last published in March 2014

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