Software-defined networking (SDN) is a simplified and streamlined approach to networking through decoupling of management, control and forwarding planes. Traditionally, network equipment is monolithic in the sense that all these abovementioned planes are tightly integrated. With SDN, the separation allows network control to become directly programmable and the underlying infrastructure to be abstracted from applications and network services.

The foremost challenge with legacy networks can be concisely described as ‘administrative nightmare’. For a network wide change management, an IT Administrator may need to touch multiple switches, routers, firewalls, servers, etc. and update ACLs, VLANs, and quality of service (QoS) policies using individual device-level management tools. In addition, network topology, vendor switch model, and software version all must be taken into account.

Legacy networks run on vendor software and equipment and due to static nature of the networks, you are tied with that particular vendor. However, IT organizations are challenged with the need to deploy new capabilities and services in rapid response to changing business or user demands. The ability to respond, though, is delayed by vendors' equipment and software product cycles, which can take years. In addition, the OS running on the vendor equipment are typically proprietary and the hardware ASICs are built for specific purposes. Lack of standard, open interfaces limits the ability of IT administrators to tailor the network to their individual environments.

SDN can solve these challenges associated with legacy networks. First, network control is directly and centrally programmable with software-based SDN controllers, because control plane is decoupled from forwarding plane. Second, SDN lets IT administrators configure, manage, secure, and optimize network resources via dynamic and automated SDN programs/scripts, which they can write themselves, because the programs do not depend on proprietary software. Third, when implemented through open standards, SDN simplifies network design and operation, because instructions are provided by SDN controllers instead of multiple, vendor-specific devices and protocols.

Open Standard and White-Box SDN Solutions or Vendor Solutions?

Facebook and Google have created software-defined networks for their companies using open standards and white-box gear. For the last two years Bank of America has been going through a massive IT transformation to create SDN capable private cloud. However, not every organization has the technical capability and know-how to implement open standard SDN to their needs. Therefore, we see vendors such as Cisco and VMware creating SDN solutions for their customers. There are also other solutions out in the market, but Cisco and VMware SDN battle is the most heated one to note.

Following the SDN wave, both Cisco and VMware defined their SDN strategies around acquisitions. Cisco acquired Insieme while VMware acquired Nicira. Cisco's SDN solution, Cisco ACI, is a combination of software and hardware, rather than purely in software as in the case of VMware NSX . Cisco ACI requires the new generation Nexus 9000 switches, and is controlled by Application Policy Infrastructure Controllers. For existing Nexus 7000 and 5000 switches Cisco ASICs are being road-mapped for installation to enable Cisco ACI. VMware NSX, though, can run on any physical IP network. Technically, one can leverage any switch vendor such as HP, Brocade, Arista, Juniper, etc. This is a big plus for VMware NSX as it does not require costly hardware upgrades to get SDN features in existing networks.

Most probably, we will see some other very large organizations other than Facebook, Google, and Bank of America to implement white-box open standard SDN solutions on their own.

For other organizations where the capability and know-how is not present, we will see more VMware NSX deployments in small and mid-size market and more Cisco ACI deployments in large size market, because deploying Cisco's ACI requires considerable capex, while VMware NSX can be folded into existing vSphere deployments. Cisco ACI is more likely to appeal strongly to data centers and large enterprises where port density a significant driver and Cisco's enterprise base mainly consists of large enterprises, who will likely to prefer Cisco's SDN technologies in order not to go through a huge transition via another vendor such as VMware. On the other hand, VMware NSX is much easier to deploy in the short term than Cisco's ACI appealing more to smaller organizations.