Overlay networks: Understanding the basics, making it a reality
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In the first part of this series, we explored the business drivers behind network virtualization technology and the potential of a hybrid implementation. In part two, we look at network virtualization considerations for a hybrid environment.
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While SDN may eventually alter the way we architect networks, it is possible in the short term to implement network virtualization technology in a hybrid environment in which traditional and virtual technologies complement each other.
In some cases, enterprises can use hybrid switches, which will forward traffic both traditionally and using SDN instructions. It's important to remember that not all OpenFlow-capable switches also run traditional protocols; therefore, organizations must specifically inquire about switches' hybrid capabilities during their evaluation.
Another hybrid approach is to install a "greenfield patch" in the brownfield data center. Here, users build a new network segment supporting virtualization and bridge it back to the legacy infrastructure. As the greenfield virtualized segment is proven, the lessons and techniques learned could then be applied to the legacy infrastructure.
As mentioned earlier, overlay networks can be transported on top of the existing physical network, or underlay. Overlays are viewed by some as a transition mechanism to pure SDN. Whether overlays are transitional or here to stay, the fact that they are seen by the network as simply IP traffic means that organizations can introduce overlays to their legacy network with little difficulty today. In fact, several vendors count on the relative ease of overlay integration as a selling point for their network virtualization products.
More on hybrid network virtualization
VIDEO: Ethan Banks on OpenFlow and SDN
The role of network hardware in virtual overlays
Understanding the difference between SDN and network overlays
Much of network virtualization is achieved in software, so it doesn't have to be costly to experiment. In fact, there is a variety of open source software that makes it possible for companies to try out network virtualization with nominal financial investment. Open vSwitch (OVS), an open source virtual switch with a rich set of capabilities has become quite popular. Coupled with OpenStack and the Neutron plug-in for OVS, it is possible to build virtual networks running "as a service" inside a larger cloud.
Moving to network virtualization is as much a mental and operational shift as it is a shift in networking itself. For years, network upgrades have been incremental, with little overall bearing on an organization's IT process, but network virtualization is a fundamental change. The long-term benefits for an organization include a tight integration of IT operations as network consumption is absorbed into the rapid provisioning processes already enjoyed by server and storage teams.
Clearly, the notion of network virtualization is here to stay; it's an idea that has many proponents, and the number of products in the space is growing. The challenge for IT teams is in evaluating the diversity of approaches in the context of specific business needs and taking into consideration rapid technological developments.