SDN and Network Virtualization
Similar to how multiple virtual machines (VMs) share a physical server, network virtualization refers to the creation of multiple virtual networks that share a common physical network. Some of the advantages of network virtualization are that it enables VMs to cross Layer 3 boundaries without requiring manual reconfiguration of the network and it also enables multi-path forwarding of packets.
One way to implement virtual networks is by using encapsulation and tunneling techniques. This approach, referred to as a network overlay, is network agnostic, which means that network overlays can be implemented on top of any physical network. However, it also means that unlike server virtualization, network overlays can’t reserve resources such as bandwidth. This limitation, combined with the inability of network overlays to guarantee service quality means that network overlays can result in degraded application performance. In addition, network overlays don’t enable IT organizations to centralize functions such as configuration management.
It’s also possible to implement network virtualization using SDN. One way to do that is to define the virtual networks in the flow tables of the SDN switches. The SDN approach to network virtualization overcomes the limitations of the network overlay approach. In addition, with the SDN approach IT organizations also get the ability to do more granular traffic routing and to gather more intelligence about the infrastructure.
HP is an example of a vendor that has already developed an SDN network virtualization application. The application, called Virtual Cloud Networks, enables multi-tenancy and increases network scalability beyond the traditional VLAN limits. It also automates provisioning for a self-service cloud by integrating with OpenStack. The application is in use today with HP Cloud Services.
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