Building a hybrid network with SDN, network virtualization

SDN and network virtualization are new and still largely misunderstood technologies. Here's how they can combine to build a modern hybrid network.

Deployment of software-defined networking (SDN) and network virtualization technologies promises a number of key

benefits to IT organizations, including the ability to rapidly provision network resources; lower operational costs; and improve network visibility, policy and orchestration. The challenge for IT managers is to navigate the plethora of choices regarding SDN technologies to select a path that brings measurable benefits in the near term and that can grow into a next-generation network architecture. This story discusses some of the key considerations for IT managers concerning SDN and network virtualization deployments.

Defining SDN and network virtualization

SDN is defined as having the following capabilities:

  • Separation of control and data plane: The intelligence of the switch and router is split out from the packet-forwarding engine.
  • Programmability: Being able to centrally change traffic flows, partition the networks and provide application-level QoS improves network flexibility.

SDN technologies can be used in the data center, the WAN, and as part of the telecommunication (e.g., optical network) transport network.

Virtualized networks (also known as virtual overlay networks) use tunnels to create a virtual network on top of traditional (Ethernet) physical networks. Network virtualization leverages protocols like VXLAN or NVGRE to provide Layer 3 tunneling and allows for virtual machine (VM) migration across the network within the data center and from data center to data center. Examples of network virtualization technology include VMware's NSX, Microsoft, PlumGrid, Midokura, Nuage and Juniper's Contrail.

SDN and network virtualization are highly interrelated technologies with overlapping capabilities, especially in the data center context. Both have widely varied (and complex) cost models, including prices by software license, VM, subscription (monthly fee), bundled with hardware and software, free software, pay for support, and open source. Implementing them should be driven by a specific use case and may require significant customization to work well in your environment.

For the purposes of this article, SDN and network virtualization are considered together.

Current situation: Plenty of choice, lack of clarity

IT managers have a tremendous number of options with regard to the deployment of network virtualization and SDN technologies. Specific vendor strategies vary widely. Some, like VMware, offer virtual overlays that require no changes to network hardware. Others, like Cisco, are heavily dependent on, and take advantage of, network hardware-specific features to improve performance. IT managers must consider whether leading IT suppliers have the best vision or whether they should select products from innovative SDN startups.

IT managers can choose from literally dozens of (radically) different SDN and network virtualization products, including:

  • Cisco: ONE, API and OpFlex
  • VMware: NSX network virtualization software
  • Open source software: From standards bodies, including OpenFlow, OpenDayLight and OpenStack
  • Low-cost white-box switches: Broadcom or Intel silicon, with operating systems from Cumulus, Vello and Pica8
  • IT suppliers: SDN offerings (often data-center-centric) from HP, IBM, Dell
  • Innovative startups: Adara, Big Switch, Embrane, Midokura, Plumgrid, Pluribus
  • Enterprise network suppliers: Alcatel-Lucent, Arista, Brocade, Citrix, F5, Juniper, Riverbed

The variety of SDN and network virtualization offerings can confuse IT managers as to which (if any) solutions to evaluate and deploy. As a result, Web-scale service providers (e.g., Google, Facebook, Amazon, Twitter, Microsoft and Rackspace) have driven the majority of SDN deployments with specific requirements (e.g., how to rapidly scale the network) and significant in-house development resources.

SDN deployment considerations

For IT managers, the first key consideration for an SDN and network virtualization deployment is having a clear understanding of its initial use case and the specific benefits such an implementation provides. A number of SDN use cases are in current deployment, including network virtualization overlays, network monitoring, network segmentation and optimizing WAN traffic flows. All these initial deployments of network virtualization overlays or SDN controllers have focused on relatively narrow pieces of the network that have limited impact on the network underlay or physical network operations.

Here are some additional aspects of an SDN and network virtualization deployment to consider:

Centralized vs. decentralized: How do you plan to implement SDN and network virtualization? Will it be in a centralized (e.g., OpenFlow controller) architecture or a more distributed model with network protocols communicating with the physical network?

WAN, data center or network-wide: Where (in what part of the network) will you target the SDN deployment?

Overlay/underlay: Network virtualization technologies can be implemented without affecting the physical network. Do you want to logically separate your deployment or adopt a solution that is well integrated with the underlay network?

Open source vs. vendor-specific: How willing are you to implement open source solutions (which requires custom integration) compared to more integrated (and proprietary) vendor-specific solutions?

SDN resources: What are your available resources (e.g., internal, systems integrators and channel) to design, implement and support an SDN deployment? How will you train your IT personnel and help them adapt to the changes an SDN/NV deployment enables?

Future vision vs. legacy migration: What is the rate of change in your IT and network architecture? How will a potential implementation of SDN and network virtualization fit in to your longer-term IT architecture?

IT organizational structure: Who in your organization will "own" the implementation? How will this affect the structure of network, server, storage and DevOps personnel, as well as communications among them?


Implementing SDN and network virtualization can offer significant benefits to IT organizations, including rapid provisioning of network resources, migration to modern network management systems (replacing scripts and command-line interfaces, and reduced costs (both operating and capital expenses). Leading-edge organizations have successfully deployed SDN and network virtualization and have discussed their specific implementations at several conferences, including the Open Network Summit and Open Network Users Group.

The next round of SDN and network virtualization deployments is taking place now as IT managers evaluate which use cases and technology options will maximize the return on investment and be part of a long-term architectural vision for their next-generation network.


This was first published in May 2014

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