SDN as the best basis for network virtualisation

The IT landscape has developed significantly over the past 10 years. Long gone are the days when IT infrastructure was confined to on-premise PCs and servers. Today, the blossoming of cloud services, the proliferation of devices, and an increasing demand to access information anytime, anywhere now means that enterprises need to an IT infrastructure with increased flexibility and agility.

Networking in particular has advanced by leaps and bounds in just the last decade. Virtualisation in the data centre has taken off, with its adoption particularly prevalent in in the area of servers. Logically abstracting the server functions away from the hardware has proven its usefulness, however, it’s important to remember that virtualisation is not just for servers. New uses of the technology have developed, such as virtual networks in the data centre.

In early stages this took the form of simple virtual LANs. However, VLANs abstract only individual segments, not entire networks, and aren’t portable in the same sense as a virtual machine. As virtualisation capabilities have advanced, network virtualisation has been acquiring greater flexibility. In fact, the idea of a fully virtualised network is now the subject of much discussion in business IT. But is a virtual network feasible and, if so, is it beneficial?

Why Virtualise?
If you think about how a traditional physical computer operates compared to a virtual machine, a physical computer is bound by the specifications of “the box.” To increase its processing speed and storage capacity, businesses must upgrade individual components or replace the box completely. However, a virtual machine is provisioned using software that mimics the operation of a physical computer. As a result, it is more flexible. It can adapt to the changing demands of applications and any modifications that need to be made to a virtual machine can be accomplished with relative ease through a software interface, rather than opening up the case and replacing parts.

In a similar way, the physical network has suffered from certain limitations that constrain the network’s potential, particularly in the modern age of mobility and on-demand computing. Physical network components essentially consist of hardware devices of fixed sizes and capacities that are wired together in static topologies. On-demand reallocation of network resources in a hardware-based environment is nearly impossible, and applications often must conform themselves to the network. The result is a less than ideal functionality for users, as well as management challenges for IT personnel.

In a fully virtualised network the control logic is decoupled from the network’s underlying physical hardware. The physical network components retain their packet forwarding duties, but control and decision-making abilities are liberated from the device’s “bounding box.” Instead, these functions are implemented as software-based services that freely adapt to the changing circumstances of network traffic, encompass all segments, track state changes throughout the entire network, and adapt policy enforcement mechanisms like QoS according to application requirements. Through this decoupling, it becomes possible to build useful virtual networks. These virtual networks encapsulate all network functions into an abstraction layer that still looks and behaves like a normal network from the perspective of an application.

Building a Virtualised Network
While it is possible to build virtualised networks today using a number of different techniques, software-defined networking (SDN) is the subject of much discussion, rapidly becoming the preferred method of today's business. SDN provides the necessary decoupling that allows the control plane to be operated completely independent of the forwarding plane. It establishes a framework to create a virtualised network that appears to upper-layer services, such as operating systems and applications, as though it were an ordinary physical network. This allows services and applications to be provided without needing to be configured for a different environment.

In a virtual network built on SDN, network resources can be allocated as needed, just as processing capacity and storage are provisioned dynamically with a virtualised server. And by changing the focus from open protocols to open application programming interfaces (APIs), SDN-based virtual networks enable new degrees of programmable flexibility – limited only by the vision of the developer.

Building a virtual network without using SDN is certainly possible, but it is probably not as useful. Virtualisation maps multiple logical networks across a common physical fabric. However, sophisticated state management becomes a challenging technical problem when logical networks could be located just about anywhere. This is where the utility of SDN comes into play. It turns out that SDN is very good at managing large numbers of states. At the same time, it can provide a reasonable degree of operational consistency, because SDN is designed to permit changes to the forwarding plane. Without the state management capabilities that are afforded by SDN, the operational utility of network virtualisation diminishes considerably.

The end result: software-defined data centres
With SDN as the best basis for network virtualisation, entire data centres can be constructed purely of software—and, indeed, the software-defined data centre (SDDC) is the next logical step. Increasingly, proper application deployment requires finely tuned infrastructure to support it. Such tuning is becoming more and more application specific, including targeted QoS policies, just-in-time resource allocations (to cope with demand spikes), transaction awareness (for cost accounting purposes), and differentiated network paths. Monolithic network equipment cannot accommodate these diverse application-specific requirements. SDDCs eliminate large infrastructure boxes and replace them with software-based network services decoupled from the underlying hardware and dedicated to and tuned to the needs of individual applications.

The software-defined data centre delivers benefits in several important areas:
· Today’s applications are utilising more complex infrastructure requirements that can be a challenge to meet in order to ensure proper quality of service. The delicate balance of meeting each requirement without harming another process is improved by the level of abstraction made possible by the SDDC.

· Because resources are provisioned on demand, developers are free to focus on the business functionality of applications without undue concern about whether the network can respond—the network in an SDDC automatically reacts to changing application requirements.

· Combining a more consolidated and centralised control framework on top of commodity hardware means there are fewer specialised physical components that can break down and inhibit operations. In addition, centralised control brings improved visibility, which makes it more difficult for attackers to hide and conduct malicious actions.

· With a reduced need for specialised network equipment, organisations employing an SDDC will likely see reduced capital and operational expenditures. With IT budgets frequently first on the chopping block in businesses, the SDDC is an ideal way to ensure continued operations at a lower cost.

What’s next for SDN?
Just as cloud and big data have reached maturity and widespread deployment as part of an IT strategy, the software-defined market is likely to define the corporate network in the years to come. People are already starting to see the value in SDN. Initially, it was a case of people considering whether it made sense to implement software-defined infrastructures into their business. But now organisations are actually converting their networks because they see the value in a fully software-defined data centre.

For years this has been considered a legitimate possibility, but there have been concerns. Managing state changes, access control lists, and counters in logical networks with thousands of virtual nodes can be a real challenge. It turns out that SDN is very good at solving these particular challenges, and with SDN it becomes possible to build fully virtualized networks completely decoupled from the underlying hardware. And with network virtualisation, the operational problems in data centres become much simpler.

A fully software-defined data centre will be a game-changer for those organisations that successfully execute the vision. Even without being an early adopter, businesses today can look ahead and begin to make preparations, such as conducting test implementations of SDN and increasing their experience with virtualisation.

In a world of frequently shrinking IT budgets and changing technology, it’s imperative that businesses reduce operational costs, while also improving flexibility and agility. Therefore, virtualisation in the data centre is definitely worth considering. SDN-based virtual networks can provide businesses with the tools they need to deliver applications effectively while also simplifying the underlying physical infrastructure. Many businesses are already realising significant benefits from the continued proliferation of virtualisation in the data centre and it will be these organisations that will lead the way as we continue to move to a software-defined environment.