SDN, network virtualization: Are they the same?

Lee Doyle

What's the difference between SDN and network virtualization?

Network virtualization allows IT managers to consolidate multiple physical networks, divide a network into multiple segments or create software-only networks between virtual machines (VMs). The goal of network virtualization is to improve speed, automation and network management by adding new software elements. It may or may not be programmable.

Virtual networks can be created in two ways -- inside or outside the server. External software uses switches, adapters and the network to aggregate physical local area networks (LANs) into a single logical LAN, or to break a physical LAN into multiple virtual LANs (VLANs). Internal software allows virtual machines (VMs) to exchange data on a host without an external network. Examples of network virtualization offerings include VMware vShield and vSphere switches and Cisco's Nexus 1000.

Software-defined networking is defined as a network with the two following elements:

  • Separation of control and data plane. The separation of the control and data planes means that the intelligence of the switch/router is split out from the packet-forwarding engine and placed in the control plane. This may be centralized or decentralized. The main advantage of centralization is ease of network programming.
  • Programmability. This term refers to the ability to improve network flexibility by linking the application to the network, including the ability to dynamically change traffic flows and provide application-level Quality of Service (QoS).

When you compare the SDN, network virtualization definitions, it's clear that network virtualization and SDN technologies share common elements, particularly the goal of improving the agility to direct appropriate network resources to VMs in data center environments and the ability to consolidate or segment networks. Whether network virtualization is a subset of SDN or SDN is a subset of network virtualization, the two have overlapping sets of technologies with similar goals.

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