Software has been programming our networks for a long time, so how is SDN different?
It's true that software such as distributed routing algorithms and management protocols have been determining forwarding paths and setting network device parameters for a long time. However, the tools used have tended to be isolated to networking's ecology and proprietary per vendor. SDN has several big ideas that improve on things: centralized control, programmatic interfaces and integration with orchestration/automation tools.
Why is SDN better than the traditional network I have today?
How SDN can improve your network depends largely on the problem you're trying to solve. With the proper SDN solution in place, you could smooth out your operational processes, reduce human errors, or forward traffic in unconventional ways as defined by metrics unique to your organization. In short, you're gaining efficiency and flexibility.
What are the common use cases?
There are two major use cases SDN is addressing in the enterprise today. The first is to aid in network data capture and network visualization. In this use case, network traffic of interest as defined by a software policy is copied to collectors where it can be analyzed and visualized. The SDN controller is able to insert virtual taps throughout the network infrastructure and send copies of the flows from no matter where they are to wherever the analysis engine is.
The second is what could be thought of as creative forwarding, where traffic is forwarded across an engineered network path based on criteria other than traditional forwarding paradigms like OSPF, BGP or MPLS. Common applications are for special treatment of latency- or jitter-sensitive traffic, forcing selected traffic through an inspection device to improve security and "routing for dollars," where the traffic is routed across paths that are cheaper for an organization to use depending on time of day or link utilization.
Why does the Open Networking Foundation act in a closed manner, unlike the IETF or IEEE?
The ONF was created in part to facilitate rapid development of the OpenFlow protocol. OpenFlow is a vendor-independent protocol used by an SDN controller to program forwarding tables in network switches using a variety of traffic-matching conditions and actions. Speed is best accomplished with a small set of defined members with a vested interest in a specific result. If operating in the open manner like the IETF or the IEEE, the development process would necessarily be slower to be inclusive of all parties, use cases and concerns that might come up.
There has been some discussion of opening up the ONF proceedings at some point to allow the larger networking community to observe the OpenFlow specification discussions.
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