SDN介绍
软件定义网络（SDN）技术是一种新颖的云计算方法，可促进网络管理，并通过编程实现高效的网络配置，从而改善网络性能和监控。 SDN旨在解决这样一个事实，即传统网络的静态架构是分散和复杂的，而当前网络需要更大的灵活性和简单的故障排除。 SDN建议通过将网络数据包（数据平面）的转发过程与路由过程（控制平面）分离，从而将网络智能集中到一个网络组件中。控制平面由一个或多个控制器组成，这些控制器被认为是整合智能的SDN网络的大脑。然而，智能集中在安全性，可伸缩性和弹性方面有其自身的缺点，这是SDN的主要问题。 SDN自2011年出现以来，通常与OpenFlow协议（用于与网络平面元件进行远程通信，以确定跨网络交换机的网络数据包路径的目的）相关。自2012年以来，然而，许多公司已经离开了OpenFlow，并接受了不同的技术。其中包括思科系统的开放式网络环境和Nicira的网络虚拟化平台。 SD-WAN将类似的技术应用于广域网（WAN）。
A high-level overview of the software-defined networking architecture
SDN架构是：
1.直接可编程：网络控制可直接编程，因为它与转发功能分离。
2.敏捷：从转发中抽象控制可让管理员动态调整整个网络的流量，以满足不断变化的需求。
3.集中管理：网络智能（基于逻辑）集中在基于软件的SDN控制器中，该控制器可维护网络的全局视图，应用程序和策略引擎将其视为单一的逻辑交换机。
4.以编程方式配置：SDN使网络管理员能够通过动态自动化的SDN程序非常快速地配置，管理，保护和优化网络资源，这些程序可以自行编写，因为程序不依赖专有软件。
5.基于开放标准和厂商中立：通过开放标准实施时，SDN简化了网络设计和操作，因为SDN控制器提供的是指令，而不是多个供应商特定的设备和协议。
Architectural components
- SDN Application
- SDN Applications are programs that explicitly, directly, and programmatically communicate their network requirements and desired network behavior to the SDN Controller via a northbound interface (NBI). In addition they may consume an abstracted view of the network for their internal decision-making purposes. An SDN Application consists of one SDN Application Logic and one or more NBI Drivers. SDN Applications may themselves expose another layer of abstracted network control, thus offering one or more higher-level NBIs through respective NBI agents.
- SDN Controller
- The SDN Controller is a logically centralized entity in charge of (i) translating the requirements from the SDN Application layer down to the SDN Datapaths and (ii) providing the SDN Applications with an abstract view of the network (which may include statistics and events). An SDN Controller consists of one or more NBI Agents, the SDN Control Logic, and the Control to Data-Plane Interface (CDPI) driver. Definition as a logically centralized entity neither prescribes nor precludes implementation details such as the federation of multiple controllers, the hierarchical connection of controllers, communication interfaces between controllers, nor virtualization or slicing of network resources.
- SDN Datapath
- The SDN Datapath is a logical network device that exposes visibility and uncontested control over its advertised forwarding and data processing capabilities. The logical representation may encompass all or a subset of the physical substrate resources. An SDN Datapath comprises a CDPI agent and a set of one or more traffic forwarding engines and zero or more traffic processing functions. These engines and functions may include simple forwarding between the datapath‘s external interfaces or internal traffic processing or termination functions. One or more SDN Datapaths may be contained in a single (physical) network element—an integrated physical combination of communications resources, managed as a unit. An SDN Datapath may also be defined across multiple physical network elements. This logical definition neither prescribes nor precludes implementation details such as the logical to physical mapping, management of shared physical resources, virtualization or slicing of the SDN Datapath, interoperability with non-SDN networking, nor the data processing functionality, which can include OSI layer 4-7 functions.
- SDN Control to Data-Plane Interface (CDPI)
- The SDN CDPI is the interface defined between an SDN Controller and an SDN Datapath, which provides at least (i) programmatic control of all forwarding operations, (ii) capabilities advertisement, (iii) statistics reporting, and (iv) event notification. One value of SDN lies in the expectation that the CDPI is implemented in an open, vendor-neutral and interoperable way.
- SDN Northbound Interfaces (NBI)
- SDN NBIs are interfaces between SDN Applications and SDN Controllers and typically provide abstract network views and enable direct expression of network behavior and requirements. This may occur at any level of abstraction (latitude) and across different sets of functionality (longitude). One value of SDN lies in the expectation that these interfaces are implemented in an open, vendor-neutral and interoperable way.
SDN目前阵营
以传统设备厂商支持的ODL和以运营商主导的ONOS。
ODL：https://www.opendaylight.org/
下一节将讲述部署一个简单的ONOS环境。
Date：2018-3-2 Mail:BurlyLuo@foxmail.com
BurlyLuo
