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Which vision of SDN will win?

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At the end of last year, Compare the Cloud took a look at what we thought was in store for Cloud users and Cloud service providers, and one of our predictions was for a greater awareness of Software Defined Networking (SDN) to develop this year. But, if this proves to be the case, which vision of SDN will win through in 2014?

The Case for Software Defined Networking
The argument for SDN is very tempting: by applying the logic of server virtualisation to a network, we should be able to achieve the same level of abstraction and the same benefits, right? Well, the jury is out on whether it is really achievable and, in the meantime, two very different visions are emerging about how those benefits can be realised.

By applying the logic of server virtualisation to a network, we should be able to achieve the same level of abstraction and the same benefits, right?

Attempts to create a policy-defined, more centrally-managed network are not new. At CohesiveFT they’ve been developing a software defined (overlay) network since 2007. However, the success and widespread use of virtualised servers, the growing acceptance and move towards cloud computing models and the success of businesses like Facebook and Amazon in efficiently managing huge data centres has really ignited interest in the potential of SDN.

Hardly a week goes by without some new SDN-related acquisition, strategy unveiling or the like. And a schism seems to be emerging between those who see SDN as a software-only solution, which decouples the network from the physical infrastructure, and those who argue that network virtualisation must be paired with an ability to address the physical infrastructure if SDN is to have real value.

Network Virtualisation Holds All the Answers
Given where they are coming from, it is no surprise that the “decouple, decouple, decouple” argument is being led by leading hypervisor vendor, VMware. The vision for their network virtualisation platform, NSX, is to enable users to deploy a virtual network for an application at the same speed and operational efficiency that you can deploy a virtual machine.

VMware delivers this through its hypervisor virtual switch, vSwitch, and its NSX controller. The virtual switches connect to each other across the physical network using an overlay network, handle links between local virtual machines, and provide access to the physical network should a remote resource be required

An advantage of this approach is that additional services, such as distributed firewalls and load-balancers, can reside in the virtual switch, allowing for a more flexible firewalling policy and greater network efficiency. However, the strength of the solution – of taking the intelligence out of the physical infrastructure, so it is responsible only for forwarding overlay packets – is also at the core of its criticism.

An advantage of this approach is that additional services, such as distributed firewalls and load-balancers, can reside in the virtual switch.

Because it offers no visibility into the physical underlay network on which the solutions resides, there can be no insight or assistance with regards traffic engineering, fault isolation, load distribution or other essential physical network management activities.

Software Is Only Part of the Answer
Those who believe that a virtualised network which does not support communication with network switching hardware cannot represent a true SDN solution, should look no further than the words of Padmasree Warrior, Chief Technology and Strategy Officer at Cisco, who argued last year that: “Software network virtualization treats physical and virtual infrastructure as separate entities, and denies customers a common policy framework and common operational model for management, orchestration and monitoring.”

CISCO has been quick to target this perceived weakness in the VMware vision, as it promotes its own SDN vision: Application Centric Infrastructure (ACI). Through its APIC controller, CISCO will enable users to create a policy-driven infrastructure, controlling both virtual and (CISCO) hardware switches, and built around the needs of the application.

Through its APIC controller, CISCO will enable users to create a policy-driven infrastructure, controlling both virtual and (CISCO) hardware switches.

CISCO argue this approach will deliver both network virtualisation and visibility into the physical network which will enable the fine-tuning of network traffic.

Which Vision Will Win Out?
VMware have been quick to dismiss CISCO’s vision of the Application Centric Network as ‘Hardware Defined Networking’; casting it as an attempt to slow a shift in architecture specifications towards virtual networks which can run on low-cost hardware.  The commoditisation of hardware model doesn’t work, they argue, when you’re tied in to specific hardware.

But it isn’t as simple as that: the fact remains that hardware will still need to be updated to cope with changing network needs, and it will be continue to be necessary to monitor and optimise it.

I guess whichever side of the argument ultimately wins hearts and minds, the real winners here will be cloud customers and CSPs. Two major technology firms bringing to the market two different solutions and investing huge marketing efforts into promoting their own approaches will certainly raise awareness in the potential of SDN.

As SDN becomes adopted more widely, so will customer organisations’ ability to leverage the full benefit of virtualisation and Cloud computing.

For CSPs, a key benefit of virtual networks is the provision of multi-tenant isolation on a shared physical network. To this end, many CSPs are running their own proprietary SDN solutions in their environments already (as we saw from Chris Purrington’s post earlier), so this argument is really one about raising awareness about SDN and communicating the benefits.

Those benefits include helping organisations manage hybrid and multi-cloud environments in a way that helps that leverage greatest performance, efficiency and security. And so whichever vision wins out, as SDN becomes adopted more widely, so will customer organisations’ ability to leverage the full benefit of virtualisation and Cloud computing.