Data centres and their underlying network architecture must become more agile to meet the demands of virtualised networks, servers and workloads that can move into and out of data centres, while maintaining service-level agreement policies, says global research and advisory firm Gartner Research VP Neil Rickard.

An evolutionary approach is the most common to make data centre network architecture software defined because most centres are not greenfield projects, he notes.

The biggest barrier to data centre agility is the time required to provision a network. Cloud computing will increase data centre agility and lead to fewer, but denser corporate data centres and fewer physical servers, but more virtual machines.

Software-defined networking also enables virtual machine mobility, enabling information technology departments to decide when to move workloads, such as applications, shared files and email servers, freely between servers, data centres and into and out of public clouds, depending on capacity and price, highlights Rickard.

Further, data centres will also become more efficient by applying the practices of virtualisation and software-defined networking.

Networks must be re-configured to support workload consolidation and redesigned to support virtual machine portability and enable network configuration to follow the movement of workloads dynamically. Network con- figurations and control must be tied to virtual servers and applications as they move around the data centre and beyond. Software-defined networking can help enable this, says Rickard.

Virtual switches (VSwitches) should be deployed at the data centre network edge. Top-of-rack and blade switches switch traffic locally and then offload the relevant packets to the rest of the network and around the data centre in one-tier or two-tier switch architectures. This lowers latency, leads to simpler configurations and lower hardware and support costs.

“Data centres must create flat layer-2 (data link) networks, which require that the entire data centre and all interconnected data centres in a cluster use virtual local area networks and reduce the number of layers of switches. In any case, it is good practice to have fewer switches, which reduces power consumption and configuration management. It also simplifies the network and reduces latency,” notes Rickard.

“Server virtualisation software requires that, for servers to be in the same resource pool, they must be on the same layer-2 subnet. This simplifies the configuration requirements and reduces latency, as traffic is not going through unnecessary layer-3 (network layer) routing processes, but may require data centres to redesign their network architecture.”

Software-defined networking provides a flexible architecture that can deliver the robust scalable layer-2 networks that server virtualisation requires.

In a software-defined network environment, the control plane of switches is removed and replaced by central controllers, which can be devices or a virtual overlay onto existing equipment. These networks will be necessary for data centres and companies to stay abreast of the increases in data traffic and cloud services.

Further, software-defined networking will not remove the need for network operations staff, who will still have to manage the topology of the data centre and handle cabling and troubleshooting.

Software-defined networking sees control placed centrally for end-to-end policy-based path management, which offers integration with virtual servers and applications, while the network can be device or virtual device based, but remains immature.

This type of networking will enable data centres to address many of the performance issues, as it reduces the time required to provision network resources for a new virtual machine from weeks to minutes.

“Software-defined networks are a new way of creating networks and is a disruptive technology, entailing the separation of the control layer from the data plane, removing the need for individual device control. Incoming traffic will be routed to its destination, based on a holistic view of the entire network, enabling the most efficient routing to be determined. Traffic can also be prioritised, enabling the inclusion of further resilience in these networks.”

There are no dominant software-defined networking companies in the market and the recommendation to companies is to approach software-defined networking tactically, targeting specific capabilities that virtualisation and software-defined networking provides, such as rapid virtual local area network provisioning, network provisioning, virtual orchestration or service chaining, he concludes.