Is SDN a distributed or centralized architecture?
Let's start with what a distributed network architecture can mean in the context of software-defined networking (SDN). Distributed networking, as opposed to centralized, can describe varying degrees of centralization to decentralization communications via a network. With regard to software-defined network architecture, distributed communications will apply to the following elements:
- Intraserver traffic within the data center
- Local area networks (LANs) with connections to compute and storage resources located elsewhere
- Wide area networks (WANs): geographically distributed networks.
If we define communications within the data center as the most centralized and WANs as the most distributed, we can think of the Internet as an example of a highly decentralized network.
The network industry has debated the benefits and drawbacks of highly centralized and highly distributed network architectures for decades. In general, "centralized" means faster and easier to manage, and "decentralized" means the ability to scale and redundancy (e.g., "five 9s" or 99.999% reliability).
SDN technology can and will be deployed across a wide range of network architectures, which means we'll see SDN within the data center, SDN in the campus LAN and SDN in the WAN. A number of suppliers describe their SDN offerings as "distributed," including IBM's Distributed Overlay Virtual Network (DOVE) and ConteXtream's distributed virtual layer 4-7 switch.
So the short answer is yes -- software-defined networks can either be centralized in a single data center or distributed across a campus or wide area network, depending on the needs of the organization or service provider.
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