flow action to open的意思？
如何用英语口语表达“一闪而过的念头”？
【导语】英语⼝语学习是⼀个⽇积⽉累的过程，每天进步⼀点点，虽然短时间内效果不显著，长期坚持下来语⾔⽔平却能得到⼤幅度的提升。
⼀起来看看吧！更多相关讯息请关注！1. Occur to有个想法突然在你的脑中闪现，突然想起或想到可以⽤occur to⽐如：A good idea occurred to me.我想到了⼀个好主意。
⼜或者：It occurred to me that I had left the door unlocked.我忽然想起忘了锁门了。
2. Flash on这个短语⽣动形象地表达了⼀种秒懂的惊喜。
灵感⼀来，就像放出⼀道闪电。
例：It flashed on me that he was her husband.我忽然意识到他是她的丈夫。
3. Bring to mind神马东东悄悄进⼊了你的脑海⾥，这个短语的意思是“想起”，还有些回忆的意味在其中。
例：I know it happened, but I can't bring it to mind.我知道有这么回事, 但回忆不起来了。
4. Ring a bellRing a bell叮铃⼀声，好似提醒了你什么。
某个⼈或者某些事，提起来好熟悉，有种“似曾相识”的赶脚，⽤上这个词组就⽣动了许多~ 例：I can't remember her name but her face rings a bell.我记不起她的姓名, 但是她的脸我很熟悉。
5. Cross one's mind表⽰某种念头在脑海中出现，英⽂还可以说cross one's mind，也是相当形象。
⽐如：It never crossed my mind that Lisa might be lying.我从来没想过丽莎会说谎。
【个人总结系列-11】Openflow协议的理解-学习及总结
Openflow协议的理解-学习及总结Openflow协议概述OpenFlow协议是斯坦福大学的Nick McKeown提出的，随着OpenFlow协议的提出，SDN（Software Defined Network）也逐渐得到人们以及网络设备运营商的关注。
OpenFlow协议的主要思想就是将传统网络交换机数据包转发的过程分离开来，原来由交换机一步完成的转发动作现由2种设备协作完成，分别是支持openflow协议的交换机（假设为OVS）和控制器（以下称controller）。
OVS 里面维护了一个叫做流表（flow table）的东西，用来指定转发的策略，流表是在controller的控制下生成的，并且controller随时可以维护流表（删除、添加、修改流表项）。
所以网络管理人员可以很容易自己定义网络的行为，这也是SDN的原因。
在OpenFlow网络中数据包的转发流程是这样的：OVS接收到数据以后，通过和流表项进行匹配决定这个包的走向（转发、丢弃还是传给controller等），所以流表就相当于控制的策略，定义网络的行为只要在controller端对流表进行操作即可。
这就涉及到controller和OVS之间通信和交流的问题，而Controller和OVS之间通信的消息格式、内容及种类就是OpenFlow协议的主要内容。
OVS通过secure channel和controller进行通信，而且通信内容是通过TLS加密的，从secure channel发出和接收到的信息是和交换机接收到的数据包（到达的数据包）是不一样的，他们不经过流表的处理，OVS和controller的关系如下图所示[1]：图2-1-1 OVS和控制器的关系所以OpenFlow网络中最重要的就是流表（流表的结构和匹配的过程）和controller与OVS之间的通信。
下面主要介绍一下自己理解的这两块的内容。
流表每个交换机包括许多流表和一个组表，流表从0开始进行编号。
openflow通信流程解读
前言接触了这么久的SDN，Openflow协议前前后后也读过好多遍，但是一直没有时间总结一下自己的一些见解。
现在有时间了，就写一写自己对Openflow协议通信流程的一些理解。
SDN中Switch和controller在SDN中很重要的两个实体是Switch跟Controller。
Controller在网络中相当于上帝，可以知道网络中所有的消息，可以给交换机下发指令。
Switch就是一个实现Controller指令的实体，只不过这个交换机跟传统的交换机不一样，他的转发规则由流表指定，而流表由控制器发送。
switch组成与传统交换机的差异switch组成switch由一个Secure Channel和一个flow table组成，of1.3之后table变成多级流表，有256级。
而of1.0中table只在table0中。
∙Secure Channel是与控制器通信的模块，switch和controller之间的连接时通过socket连接实现。
∙Flow table里面存放这数据的转发规则，是switch的交换转发模块。
数据进入switch之后，在table中寻找对应的flow进行匹配，并执行相应的action，若无匹配的flow则产生packet_in（后面有讲）of中sw与传统交换机的差异∙匹配层次高达4层，可以匹配到端口，而传统交换机只是2层的设备。
∙运行of协议，实现许多路由器的功能，比如组播。
∙求补充！！（如果你知道，请告诉我，非常感谢！）openflow的switch可以从以下方式获得∙实体of交换机，目前市场上有一些厂商已经制造出of交换机，但是普遍反映价格较贵！性能最好。
∙在实体机上安装OVS，OVS可以使计算机变成一个openflow交换机。
性能相对稳定。
∙使用mininet模拟环境。
可以搭建许多交换机，任意拓扑，搭建拓扑具体教程本博客有一篇。
性能依赖虚拟机的性能。
controller组成控制器有许多种，不同的语言，如python写的pox,ryu，如java写的floodlight 等等。
open的详细用法
open的详细用法o?pen 11.开着的，打开的He threw the door open and ran down the stairs. 他猛地打开门，往楼下跑去。
2.〔眼睛或嘴〕未合上的，张开的I was so sleepy, I couldn’t keep my eyes open. 我困得眼睛都睁不开了。
He was fast asleep with his mouth wide open. 他大张着嘴，睡得很熟。
3.开阔的，未围上的There was open ground at t he end of the lane. 小巷的尽头有一片开阔地。
open countryside/country?At weekends people want to leave the town for open countryside. 到了周末，人们就想离开城镇到开阔的乡村去。
4.无顶的，无遮盖的The president was riding with his wife in an open car. 总统和他的夫人乘坐一辆敞篷车。
?an open drain 排水明沟open to the sky/air/elements?Many of the tombs had been robbed and left open to the sky. 许多坟墓被盗，裸露在青天白日之下。
5.the open air户外，室外，露天→ open-airJane wanted to rush to the door and get out into the open air. 简很想冲到门口，到外面去。
in the open air?The dancing was outside, in the open air. 舞会在户外举行。
6.[not before noun,不用于名词前] 开放的，营业的The museum is open daily in the summer months. 夏季里这座博物馆每天开放。
OpenFlow网络技术原理介绍
TABLE IN_PORT ANY LOCAL
NORMAL
FLOOD
代表传统的非OpenFlow交换机管道
代表传统的非OpenFlow交换机泛洪
14
15
OpenFlow Processing Pipeline
OpenFlow管道处理流程
Packet in
Ingress port
Action OpenFlow管道 Action set Set=0
Table 0
Packet+ Ingress port+ metadata
Table 1
Table Action n set
Discovery 仅仅是理论和功能建模 Data
2
5
Ethane架构
Ethane 中央控制器 Ethane交换机
中央控制器 ?
Ethane交换机
奠定OpenFlow 技术基础
2
6
SDN架构
SDN 应用层 控制层 基础设施层 应用层
API
应用程序
API API
控制层
SDN 控制软件
提取报文的 特征信息 （mac、ip等）
下发Flow-mode 消息到交换机， 添加流表项
yes 按照匹配的 流表项转发
下发packet out 报文，动作为 out到table
25
25
报文上送控制器的处理过程
25
26
单播报文流表转发
报文从 表0开始 yes
open_flow简介
Datapath
一个简单的OF网络实例（三）
Step 2:启用 nox 程序，监听 2525 端口，并运行 python 的 l2 交换组件。
运行NOX程序， controller和 switch连接
一个简单的OF网络实例（四）
Step3：运行交换机上的安全通道，来连接 datapath 和 nox。
包处理流程
从网络中 获取一个 包 可先依照自动 生成树协议处 理（非必须） 和流表的 包头域对 比
NO 转发给 controller处理
是否有匹 配项 YES
相应计数器加 1
按照匹配流表 项中的action 执行
Open Flow协议的消息类型
OF协议支持三种消息类型：controller-to-switch，asynchronous（异步） 和symmetric（对称），每一类消息又有多个子消息类型。 •controller-to-switch 消息由控制器发起，用来管理或获取switch 状态； •asynchronous 消息由switch 发起，用来将网络事件或交换机状态变化 更新到控制器； •symmetric 消息可由交换机或控制器发起。
symmetric 消息
symmetric 消息也不必通过请求建立，包括 Hello、Echo、Vendor 等。 Hello 交换机和控制器用来建立连接。 Echo 交换机和控制器均可以向对方发出 Echo 消息，接收者则需要回复 Echo reply。 该消息 用来测量延迟、是否连接保持等。 Vendor 交换机提供额外的附加信息功能。为未来版本预留。
asynchronous 消息
asynchronous 不需要控制器请求发起，主要用于交换机向控制器通知状态变化等事 件 信息。主要消息包括 Packet-in、Flow-removed、Port-status、Error 等。 Packet-in 交换机收到一个网包，在流表中没有匹配项，则发送 Packet-in 消息给控制器。如果 交换机缓存足够多，网包被临时放在缓存中，网包的部分内容（默认 128 字节）和 在交换机缓存中的的序号也一同发给控制器；如果交换机缓存不足以存储网包，则 将整个网包作为消息的附带内容发给控制器。 Flow-removed 交换机中的流表项因为超时或修改等原因被删除掉，会触发 Flow-removed 消息。 Port-status 交换机端口状态发生变化时（例如 down 掉），触发 Port-status 消息。 Error 交换机通过 Error 消息来通知控制器发生的问题。
如何选择流开型调节阀和流关型调节阀
如何选择如何选择流开流开流开型调节阀型调节阀型调节阀和流关和流关和流关型型调节阀一、定义流开型调节阀FTO(Flow To Open)：在调节阀节流口，介质的流动方向与阀门的打开方向一致。
流关型调节阀FTC(Flow To Close)：在调节阀节流口，介质的流动方向与阀门的打开方向相反。
二、各自特点1、流开型调节阀FTO 优点：稳定，开启力矩小，关闭时填料不受压；缺点：自洁性能和密封性较差，寿命较短2、流关型调节阀FTC 优点：自洁性能和密封性好，有负吸作用关闭速速快，可提高密封面抗冲刷的能力，使用寿命相对较长；缺点：稳定性差，开启力矩大，执行机构选择不当会导致阀芯接近关闭时运动速度过快造成阀门震荡三、如何选择流关阀在关闭后，阀芯的关闭压力除了执行机构的作用力之外还有阀前后压差在阀芯上的作用力；在关闭过程中，介质的惯性（水锤作用），会对阀芯产生加速关闭运动的作用力，造成阀门的加速关闭和在关闭时产生剧烈冲击。
对于依靠平衡力（如气动薄膜和弹簧的平衡，活塞两端压力平衡）控制阀位的执行机构来说，必须使用执行力远大于水锤力，并附加反应速度较快的定位器来保持阀门运动速度稳定。
因此，通常情况下，调节阀采用流开，主要是开启力矩小，关闭时填料不受压。
特殊情况下，比如有闪蒸时应采用流关。
需要根据具体工况进行选择。
四、电力系统各个位置调节阀选型对于一些压差较小的位置（如凝结水调节阀、高低加正常疏水调节阀等），由于对执行机构的力矩要求较小，选择流开和流关对执行机构的要求没太大的区别，因此都选择流开型调节阀。
对于一些压差大的位置，尤其是容易出现气蚀的位置（如给水旁路调节阀，减温水调节阀，锅炉连排调节阀等），往往选择流关型调节阀。
flow的用法及搭配
flow的用法及搭配"Flow"是一个多义词，可用作名词或动词。
作为名词，"flow"指的是液体、气体或其他物质的流动，也可指连贯性强的语言、音乐或艺术表演等。
在这种情况下，它的常见搭配有：1. Blood flow (血流): a measure of how well blood circulates in the body2. Water flow (水流): the movement of water in a river, pipe, or other conduit3. Traffic flow (交通流): the movement of vehicles on a road or highway4. Data flow (数据流): the movement of information within a computer system or network5. Creative flow (创造力迸发): the state of being fully absorbed and focused in a creative activity作为动词，"flow"指的是液体、气体或其他物质的流动，也可指思想、信息或话语的连贯性流动。
在这种情况下，它的常见搭配有：1. Flow of water (水流): the movement of water in a specific direction2. Flow of traffic (交通流量): the movement of vehicles in a specific direction on a road or highway3. Flow of information (信息流): the movement of information from one place to another4. Flow of ideas (思想流畅): the continuous generation and exchange of ideas5. Flow of conversation (交谈流畅): the smooth and uninterrupted exchange of dialogue无论作为名词还是动词，"flow"都表示物质、信息或思想的连续性和顺畅性。
SDN和Openflow详解mininet与opendaylight环境搭建与测试
基于OpenFlow的SDN技术1. SDN与OpenFlow技术简介SDN指的是软件定义网络。
你可以这样去理解SDN：如果将网络中所有的网络设备视为被管理的资源，那么参考操作系统的原理，可以抽象出一个网络操作系统（Network OS）的概念—这个网络操作系统一方面抽象了底层网络设备的具体细节，同时还为上层应用提供了统一的管理视图和编程接口。
这样，基于网络操作系统这个平台，用户可以开发各种应用程序，通过软件来定义逻辑上的网络拓扑，以满足对网络资源的不同需求，而无需关心底层网络的物理拓扑结构。
云计算的发展，是以虚拟化技术为基础的。
云计算服务商以按需分配为原则，为客户提供具有高可用性、高扩展性的计算、存储和网络等IT资源。
虚拟化技术将各种物理资源抽象为逻辑上的资源，隐藏了各种物理上的限制，为在更细粒度上对其进行管理和应用提供了可能性。
近些年，计算的虚拟化技术（主要指x86平台的虚拟化）取得了长足的发展；相比较而言，尽管存储和网络的虚拟化也得到了诸多发展，但是还有很多问题亟需解决，在云计算环境中尤其如此。
OpenFlow和SDN尽管不是专门为网络虚拟化而生，但是它们带来的标准化和灵活性却给网络虚拟化的发展带来无限可能。
SDN的最重要特征：将传统网络设备的数据转发（data plane）和路由控制（control plane）两个功能模块相分离，通过集中式的控制器（Controller）以标准化的接口对各种网络设备进行管理和配置，那么这将为网络资源的设计、管理和使用提供更多的可能性，从而更容易推动网络的革新与发展。
OpenFlow是实现SDN最常用的的一种协议，OpenFlow的原理和基本架构如下图。
其实，这张图还很好地表明了OpenFlow Switch规范所定义的范围—从图上可以看出，OpenFlow Switch规范主要定义了Switch的功能模块以及其与Controller之间的通信信道等方面。
英语里的各种开和关的表达方式
英语里的各种开和关的表达方式1. openopen的原意是把封起来的或合起来的东西打开或揭开，强调从紧闭的状态向开放状态的移动。
反义词为close，意为"关闭，合上"。
(1). 打开门窗/ 容器、书等——open the door / window/ box/ bookOpen the window and let the fresh air in. 打开窗户，让新鲜空气进来。
Open your book and turn to page six. 打开书翻到第六页。
(2). 睁开眼睛，张开嘴巴——open the eyes / open the mouthYou are running a fever. Please open your mouth and I'll check it.你在发烧。
请张开嘴让我检查一下。
Close your eyes lightly and take a deep breath.轻轻地闭上眼睛，深呼吸。
2. turn on我们知道turn有"转动，旋转"的意思，所以turn on 也可以理解为拧开。
通常用于某种设备或者电器类。
比如：电视，灯，收音机之类。
其反义短语是: turn off，意为"关掉"。
看例句：(1). Remember to turn off the lights before you leave. 在你离开之前记得关灯。
(2). It's news time. Turn on the radio. 新闻时间到了，打开收音机。
3. switch onswitch on 有"接通，开启，合闸"的意思，用于"打开"一些电器设备，使其开始工作。
比如：电脑，机器等。
其反义短语为switch off，意为："关掉，切断"。
(1). He switched on the computer and began to work. 他打开电脑开始工作。
toopen的用法
toopen的用法在英文中，“to open”是动词“open”的不定式形式。
不定式常常用于表达目的、原因、结果或作为某些动词或介词的宾语。
以下是“to open”的一些常见用法：1.作为目的状语：o I have a key to open the door. (我有一把开门的钥匙。
)o We'll have to wait for someone to open the gate. (我们得等有人来开门。
)2.作为宾语：o She likes to open presents. (她喜欢打开礼物。
)o Can you teach me how to open this bottle? (你能教我如何打开这个瓶子吗？)3.与某些动词搭配使用：o begin to open (开始打开)o attempt to open (试图打开)o strive to open (努力打开)4.在形容词之后：o The door is difficult to open. (这扇门很难打开。
)o The book is easy to open. (这本书很容易打开。
)5.在名词之后：o She has the ability to open any lock. (她有打开任何锁的能力。
)o The key has the function to open the door. (这把钥匙有打开门的功能。
)6.作为介词宾语：o The key is used to open the door. (这把钥匙是用来开门的。
)o He needs a tool to open the bottle. (他需要一个工具来打开瓶子。
)7.在条件句中：o If you want to open the box, you need the right key. (如果你想打开这个盒子，你需要正确的钥匙。
)此外，“to open”还可以作为非谓语动词参与句子的构建，具体用法取决于它在句子中的位置和作用。
形容提前了解风吹草动的成语
形容提前了解风吹草动的成语英文版In Chinese culture, there is a famous idiom that describes being able to anticipate and prepare for something before it happens. This idiom is "风吹草动" (fēng chuī cǎo dòng), which literally translates to "the wind blowing the grass and moving." This idiom is used to convey the idea of being able to sense even the slightest change or movement in a situation and take appropriate action before it becomes a problem.Being able to anticipate and understand the signs of impending change is a valuable skill in many aspects of life. Whether it is in business, relationships, or personal endeavors, being able to "风吹草动" can help you stay ahead of the game and avoid potential pitfalls. By paying attention to small details and being aware of subtle shifts in the environment, you can better prepare yourself for what lies ahead.In a world that is constantly changing and evolving, the ability to anticipate and adapt to these changes is more important than ever. By embracing the wisdom of the idiom "风吹草动," we can learn to be more observant, proactive, and prepared for whatever life throws our way.形容提前了解风吹草动的成语在中国文化中，有一个著名的成语描述了在事情发生之前就能够预见并做好准备。
OpenFlow1.3协议总结
OpenFlow1.3协议总结OpenFlow1.3协议总结OpenFlow1.3协议总结 (1)1介绍 (4)2交换机组成 (4)3名称解释 (4)4端⼝ (4)5OpenFlow表 (5)5.1Pipeline处理 (5)5.2Flow Table (6)5.3Match (6)5.4Table-miss (6)5.5流表项删除 (6)5.6组表 (7)5.7Meter Table (7)5.8Counters (8)5.9Instructions (8)6OpenFlow1.3版本协议新增消息 (10)7OpenFlow Protocol (10)7.1OpenFlow Header (10)ofp_header (10)7.2Common Structures (11)7.2.1端⼝ (11)ofp_port (12)7.2.2队列 (14)ofp_packet_queue (14)7.2.3匹配域 (15)struct ofp_match (15)ofp_oxm_experimenter_header (17)7.2.4Flow Instruction Structures (17)ofp_instruction (17)ofp_instruction_goto_table (17)ofp_instruction_write_metadata (17)ofp_instruction_actions (17)ofp_instruction_meter (18)ofp_instruction_experimenter (18) 7.2.5Action Structures (18)ofp_action_header (18)ofp_action_output (18)ofp_action_group (19)ofp_action_set_queue (19)ofp_action_mpls_ttl (19)ofp_action_pop_mpls (19)ofp_action_set_field (19)ofp_action_experimenter_header (19) 7.3Controller-to-Switch Messages (19) 7.3.1Handshake (19)ofp_switch_features (20)7.3.2交换机配置 (20)ofp_switch_config (20)7.3.3流表配置 (21)ofp_table_mod (21)7.3.4Modify State Messages (21)ofp_flow_mod (21)ofp_group_mod (23)ofp_bucket： (23)ofp_port_mod (24)ofp_meter_mod (24)ofp_mater_band_header (25)ofp_meter_band_drop (25)ofp_meter_band_dscp_remark (25) ofp_meter_band_experimenter (25) 7.3.5Multipart Messages (25)ofp_multipart_request (26)ofp_multipart_reply (26)ofp_flow_stats_request (27)ofp_flow_stats (28)ofp_aggregate_stats_request (28)ofp_aggregate_stats_reply (28)ofp_table_stats (29)ofp_table_feature (29)ofp_table_feature_prop_type (30)ofp_table_feature_prop_header (30)ofp_table_feature_prop_instructions (30)ofp_table_feature_prop_next_tables (30)ofp_table_feature_prop_actions (30)ofp_table_feature_prop_oxm (31)ofp_table_feature_prop_instructions (31)ofp_port_stats_request (31)ofp_port_stats (32)ofp_port (33)ofp_queue_stats_request (33)ofp_queue_stats (33)ofp_group_stats_request (34)ofp_group_stats (34)ofp_group_desc (34)ofp_group_features (34)ofp_group_feature (35)ofp_meter_multipart_stats (35)ofp_meter_band_stats (35)ofp_meter_multipart_request (35)ofp_meter_config (35)ofp_meter_features (36)ofp_experimenter_multipart_header (37)7.3.6队列配置信息 (37)ofp_queue_get_config_request (37)ofp_queue_get_config_reply (37)7.3.7Packet_Out消息 (37)ofp_packet_out (37)7.3.8Barrier Message (38)7.3.9Role Request Message (38)ofp_role_request (38)7.3.10Set Asynchronous Conguration Message (38) 7.4Asynchronous消息 (39)7.4.1Packet-In Message (39)7.4.2Flow Removed Message (39)7.4.3Port Status Message (40)7.4.4Error Message (41)7.5Symmetric消息 (45)7.5.1Hello (45)7.5.2Echo Request (45)7.5.3Echo Reply (45)7.5.4Experimenter (46)1介绍2交换机组成OpenFlow的交换机包括⼀个或多个流表和⼀组表，执⾏分组查找和转发，和到⼀个外部控制器OpenFlow的信道。
OpenFlow消息
OpenFlow消息☞Openflow消息总共分为三⼤类：1、Controller‐to‐Switch控制器⾄交换机消息此类消息由控制器主动发出 Features ⽤来获取交换机特性 Configuration ⽤来配置Openflow交换机 Modify‐State ⽤来修改交换机状态(修改流表) Read‐Stats ⽤来读取交换机状态 Send‐Packet ⽤来发送数据包 Barrier 阻塞消息 2、Asynchronous 异步消息此类消息由交换机主动发出 Packet‐in ⽤来告知控制器交换机接收到数据包 Flow‐Removed ⽤来告知控制器交换机流表被删除 Port‐Status ⽤来告知控制器交换机端⼝状态更新 Error ⽤来告知控制器交换机发⽣错误 3、Symmetric 对称消息，可以由控制器或交换机主动发起 Hello ⽤来建⽴Openflow连接 Echo ⽤来确认交换机与控制器之间的连接状态 Vendor ⼚商⾃定义消息☞Openflow消息格式 Openflow协议数据包由Openflow Header和Openflow Message两部分组成 Openflow header的结构： Openflow Message结构与具体消息类型有关： Openflow消息类型：☞Openflow Channel openFlow Channel是指交换机跟Controller之间的连接通道，可以是外带管理通道（交换机⾯板上跟Console⼝在⼀起的那个单独的Ethernet端⼝，物理上跟业务端⼝分离），也可以是带内管理⼝（复⽤业务端⼝），现在常见的都是带外管理⼝，主要原因是简单，⽤带内⼝需要配置交换芯⽚和协议栈。
openFlow Channel连既可以是TCP连接，也可以是加密的TLS连接，由设备商或者⽤户⾃⾏决定⽤哪种。
使⽤TCP/TLS连接主要是为了保证可靠性。
OpenFlow-Enabling-Innovation-in-Campus-Network以及中文翻译
附录A 外文原文OpenFlow: Enabling Innovation in Campus NetworksNick McKeown Stanford University Guru Parulkar Stanford UniversityTom AndersonUniversity of WashingtonLarry PetersonPrinceton UniversityHari BalakrishnanMITJennifer RexfordPrinceton UniversityScott Shenker University of California,BerkeleyJonathan Turner Washington University inSt. LouisThis article is an editorial note submitted to CCR. It has NOT been peer reviewed.Authors take full responsibility for this article’s technical ments can be posted through CCR Online.ABSTRACTThis whitepaper proposes OpenFlow: a way for researchers to run experimental protocols in the networks they use every day. OpenFlow is based on an Ethernet switch, with an internal flow-table, and a standardized interface to add and remove flow entries. Our goal is to encourage networking vendors to add OpenFlow to their switch products for deployment in college campus backbones and wiring closets. We believe that OpenFlow is a pragmatic compromise: on one hand, it allows researchers to run experiments on heterogeneous switches in a uniform way at line-rate and with high port-density; while on the other hand, vendors do not need to expose the internal workings of their switches. In addition to allowing researchers to evaluate their ideas in real-world traffic settings, OpenFlow could serve as a useful campus component in proposed large-scale testbeds like GENI. Two buildingsat Stanford University will soon run OpenFlow networks, using commercial Ethernet switches and routers. We will work to encourage deployment at other schools; and we encourage you to consider deploying OpenFlow in your university network too.Categories and Subject DescriptorsC.2 [Internetworking]: RoutersGeneral TermsExperimentation, DesignKeywordsEthernet switch, virtualization, flow-based1. THE NEED FOR PROGRAMMABLE NETWORKSNetworks have become part of the critical infrastructure of our businesses, homes and schools. This success has been both a blessing and a curse for networking researchers; their work is more relevant, but their chance of making an impact is more remote. The reduction in real-world impact of any given network innovation is because the enormous installed base of equipment and protocols, and the reluctance to experiment with production traffic, which have created an exceedingly high barrier to entry for new ideas. Today, there is almost no practical way to experiment with new network protocols (e.g., new routing protocols, or alternatives to IP) in sufficiently realistic settings (e.g., at scale carrying real traffi c) to gain the confidence needed for their widespread deployment. The result is that most new ideas from the networking research community go untried and untested; hence the commonly held belief that the network infrastructure has “ossified”.Having recognized the problem, the networking community is hard at work developing programmable networks, such as GENI [1] a proposed nationwide research facility for experimenting with new network architectures and distributed systems. These programmable networks call for programmable switches and routers that (using virtualization) can process packets for multiple isolated experimental networks simultaneously. For example, in GENI it is envisaged that a researcher will be allocated a slice of resources across the whole network, consisting of a portion of network links, packet processing elements (e.g. routers) and end-hosts; researchers program their slices to behave as they wish. A slice could extend across the backbone, into access networks, into college campuses, industrial research labs, and include wiring closets, wireless networks, and sensor networks.Virtualized programmable networks could lower the barrier to entry for new ideas, increasing the rate of innovation in the network infrastructure. But the plans for nationwide facilities are ambitious (and costly), and it will take years for them to be deployed.This whitepaper focuses on a shorter-term question closer to home: As researchers, how can we run experiments in our campus networks? If we can figure out how, we can start soon and extend the technique to other campuses to benefit the whole community.To meet this challenge, several questions need answering, including: In the early days, how will college network administrators get comfortable putting experimental equipment (switches, routers, access points, etc.) into their network? How will researchers control a portion of their local network in a way that does not disrupt others who depend on it? And exactly whatfunctionality is needed in network switches to enable experiments? Our goal here is to propose a new switch feature that can help extend programmability into the wiring closet of college campuses.One approach -that we do not take -is to persuade commercial “name-brand” equipment vendor s to provide an open, programmable, virtualized platform on their switches and routers so that researchers can deploy new protocols, while network administrators can take comfort that the equipment is well supported. This outcome is very unlikely in the short-term. Commercial switches and routers do not typically provide an open software platform, let alone provide a means to virtualize either their hardware or software. The practice of commercial networking is that the standardized external interfaces are narrow (i.e., just packet forward ing), and all of the switch’s internalflexibility is hidden. The internals di ffer from vendor to vendor, with no standard platform for researchers to experiment with new ideas. Further, network equipment vendors are understandably nervous about opening up interfaces inside their boxes: they have spent years deploying and tuning fragile distributed protocols and algorithms, and they fear that new experiments will bring networks crashing down. And, of course, open platforms lower the barrier-to-entry for new competitors.A few open software platforms already exist, but do not have the performance or port-density we need. The simplest example is a PC with several network interfaces and an operating system. All well-known operating systems support routing of packets between interfaces, and open-source implementations of routing protocols exist (e.g., as part of the Linux distribution, or from XORP [2]); and in most cases it is possible to modify theoperating system to process packets in almost any manner (e.g., using Click [3]). The problem, of course, is performance: A PC can neither support the number of ports needed for a college wiring closet (a fan out of 100+ ports is needed per box), nor the packet-processing performance (wiring closet switches process over 100Gbits/s of data, whereas a typical PC struggles to exceed 1Gbit/s; and the gap between the two is widening).Existing platforms with specialized hardware for line-rate processing are not quite suitable for college wiring closets either. For example, an ATCA-based virtualized programmable router called the Supercharged Planet Lab Platform [4] is under development at Washington University, and can use network processors to process packets from many interfaces simultaneously at line-rate. This approach is promising in the long-term, but for the time being is targeted at large switching centers and is too expensive for widespread deployment in college wiring closets. At the other extreme is NetFPGA [5] targeted for use in teaching and research labs. NetFPGA is a low-cost PCI card with a user-programmable FPGA for processing packets, and 4 ports of Gigabit Ethernet. NetFPGA is limited to just four network interfaces—insufficient for use in a wiring closet.Thus, the commercial sol utions are too closed and inflex ible and the research solutions either have insufficient performance or fan out, or are too expensive. It seems unlikely that the research solutions, with their complete generality, can overcome their performance or cost limitations. A more promising approach is to compromise on generality and to seek a degree of switch flexibility that is:Figure 1 Idealized OpenFlow Switch. The Flow Table is controlled by a remote controllervia the Secure Channel.•Amenable to high-performance and low-cost implementations.•Capable of supporting a broad range of research.•Assured to isolate experimental traffic from production traffic. •Consistent with vendors’ need for closed platforms.This paper describes the OpenFlow Switch—a specification that is an initial attempt to meet these four goals.2. THE OPENFLOW SWITCHThe basic idea is simple: we exploit the fact that most modern Ethernet switches and routers contain flow-tables (typically built from TCAMs) that run at line-rate to im plement firewalls, NAT, QoS, and to collect statistics. While each vendor’s flow-table is different, we’ve identified an interesting common set of functions that run in many switches and routers. OpenFlow exploits this common set of functions.OpenFlow provides an open protocol to program the flow-table in different switches and routers. A network administrator can partition traffic into production and research flows. Researchers can control their own flows -by choosing the routes their packets follow and the processing they receive. Inthis way, researchers can try new routing protocols, security models, addressing schemes, and even alternatives to IP. On the same network, the production traffic is isolated and processed in the same way as today.The datapath of an OpenFlow Switch consists of a Flow Table, and an action associated with each flow entry. The set of actions supported by an OpenFlow Switch is extensible, but below we describe a minimum requirement for all switches. For high-performance and low-cost the data-path must have a carefully prescribed degree of flexibility. This means forgoing the ability to specify arbitrary handling of each packet and seeking a more limited, but still useful, range of actions. Therefore, later in the paper, define a basic required set of actions for all OpenFlow switches.An OpenFlow Switch consists of at least three parts: (1) A Flow Table, with an action associated with each flow entry, to tell the switch how to process the flow, (2) A Secure Chan nel that connects the switch to a remote control process (called the controller), allowing commands and packets to be sent between a controller and the switch using (3) The OpenFlow Protocol, which provides an open and standard way for a controller to communicate with a switch. By specifying a standard interface (the OpenFlow Protocol) through which entries in the Flow Table can be defined externally, the OpenFlow Switch avoids the need for researchers to program the switch.It is useful to categorize switches into dedicated OpenFlow switches that do not support normal Layer 2 and Layer 3 processing, and OpenFlow-enabled general purpose commercial Ethernet switches and routers, to which the Open-Flow Protocol and interfaces have been added as a new feature.Dedicated OpenFlow switches. A dedicated OpenFlow Switch is a dumb datapath element that forwards packets between ports, as defined b y a remote control process. Figure 1 shows an example of an OpenFlow Switch.In this context, flows are broadly defined, and are limited only by the capabilities of the particular implementation of the Flow Table. For example, a flow could be a TCP con nection, or all packets from a particular MAC address or IP address, or all packets with the same VLAN tag, or all packets from the same switch port. For experiments involving non-IPv4 packets, a flow could be defined as all packets matching a specific (but non-standard) header.Each flow-entry has a simple action associated with it; the three basic ones (that all dedicated OpenFlow switches must support) are:1 Forward this flow’s packets to a given port (or ports). This allows packets to be routed through the network. In most switches this is expected to take place at line-rate.2 Encapsulate and forw ard this flow’s packets to a controller. Packet is delivered to Secure Channel, where it is encapsulated and sent to a controller. Typically used for the first packet in a new flow, so a controller can decide if the flow should be added to the Flow Table. Or in some experiments, it could be used to forward all packets to a controller for processing.3 Drop this flow’s packets. Can be used for security, to curb denial of service attacks, or to reduce spurious broadcast discovery traffic from end-hosts.An entry in the Flow-Table has three fields: (1) A packet header that defines the flow, (2) The action, which defines how the packets should be processed, and (3) Statistics, which keep track of the number of packets and bytes foreach flow, and the time since the last packet matched the flow (to h elp with the removal of inactive flows).In the first generation “Type 0” switches, the flow header is a 10-tuple shown in T able 1. A TCP flow could be specified by all ten fields, whereas an IP flow might not include the transport ports in its definition. Each header field can be a wildcard to allow for aggregation of flows, such as flows in which only the VLAN ID is defined would apply to all traffic on a particular VLAN.Table 1 The header fields matched in a “Type 0” OpenFlow switch.The detailed requirements of an OpenFlow Switch are defined by the OpenFlow Switch Specification [6].OpenFlow-enabled switches. Some commercial switches, routers and access points will be enhanced with the OpenFlow feature by adding the Flow Table, Secure Channel and OpenFlow Protocol (we list some examples in Section 5). Typically, the Flow Table will re-use existing hardware, such as a TCAM; the Secure Channel and Proto col will be ported to run on the switch’s operating system. Figure 2 shows a network of OpenFlow-enabled commercial switches and access points. In this example, all the Flow Tables are managed by the same controller; the OpenFlow Protocol allows a switch to be controlled by two or more controllers for increased performance or robustness. Our goal is to enable experiments to take place in an existing production network alongside regular traffic and applications. Therefore, to win theconfidence of network administrators, OpenFlow-enabled switches must isolate experimental traffic (processed by the Flow Table) from productiontraffic that is to be processed by the normal Layer 2 and Layer 3 pipeline of the switch. There are two ways to achieve this separation. One is to add a fourth action:4. Forward this flow’s packets through the switch’s nor mal processing pipeline.The other is to define separat e sets of VLANs for experimental and production traffic. Both approaches allow normal production traffic that isn’t part of an experiment to be processed in the usual way by the switch. All OpenFlow-enabled switches are required to support one approach or the other; some will support both.Additional features. If a switch supports the header formats and the four basic actions mentioned above (and detailed in the OpenFlow SwitchSpecification), then we call it a “Type 0” switch. We expect that many switches will support additional actions, for example to rewrite portions of the packet header (e.g., for NAT, or to obfuscate addresses on intermediate links), and to map packets to a priority class. Likewise, some Flow Tables will be able to match on arbitrary fields in the packet header, enabling experiments with new non-IP protocols. As a particular set of features emerges, we willdefine a “Type 1” switch.Controllers.A controller adds and removes flow-entries from the Flow Table on behalf of experiments. For example, a static controller might be a simple application running on a PC to statically establish flows to interconnect a set of test computers for the duration of an experiment. In this case the flows resemble VLANs in current networks— providing a simple mechanism toisolate experimental traffic from the production network. Viewed this way, OpenFlow is a generalization of VLANs.One can also imagine more sophisticated controllers that dynamicallyadd/remove flows as an experiment progresses. In one usage model, a researcher might control the complete network of OpenFlow Switches and be free to decide how all flows are processed.Figure 2 Example of a network of OpenFlow-enabled commercial switches and routers.A more sophisticated controller might support multiple researchers, each with different accounts and permissions, enabling them to run multiple independent experiments on different sets of flows. Flows identified as under the control of a particular researcher (e.g., by a policy table running in a controller) could be delivered to a researcher’s user-level control program which then decides if a new flow-entry should be added to the network of switches.3. USING OPENFLOWAs a simple example of how an OpenFlow Switch might be used imagine that Amy (a researcher) invented Amy-OSPF as a new routing protocol toreplace OSPF. She wants to try her protocol in a network of OpenFlow Switches, without changing any end-host software. Amy-OSPF will run in a controller; each time a new application flow starts Amy-OSPF picks a route through a series of OpenFlow Switches, and adds a flow-entry in each switch along the path. In her experiment, Amy decides to use Amy-OSPF for thetraffic entering the OpenFlow network from her own desktop PC— so she doesn’t disrupt the network for others. To do this, she defines one flow to be all the traffic entering the Open-Flow switch through the switch port her PC is connected to, and adds a flow-entry with the action “Enca psulate and forward all packets to a controller”. When her packets reach a controller, her new protocol chooses a route and adds a new flow-entry (for the application flow) to every switch along the chosen path. When subsequent packets arrive at a switch, they are processed quickly (and at line-rate) by the Flow Table. There are legitimate questions to ask about the performance, reliability and scalability of a controller that dynam ically adds and removes flows as an experiment progresses: Can such a centralized controller be fast enough to process new flows and program the Flow Switches? What happens when a controller fails? To some extent these questions were addressed in the context of the Ethane prototype, which used simple flow switches and a central controller [7]. Preliminary results suggested that an Ethane controller based on a low-cost desktop PC could process over 10,000 new flows per second —enough for a large college campus. Of course, the rate at which ne w flows can be processed will depend on the complexity of the processing required by the re searcher’s experiment. But it gives us confidence that mean ingful experiments can be run. Scalability and redundancy are possible by making acontroller (and the experiments) stateless, allowing simple load-balancing over multiple separate devices.3.1 Experiments in a Production NetworkChances are, Amy is testing her new protocol in a network used by lots of other people. We therefore want the network to have two additional properties:1 Packets belonging to users other than Amy should be routed using a standard and tested routing protocol running in the switch or router from a “name-brand” vendor.2 Amy should only be able to add flow entries for her traffic, or for any traffic her network administrator has allowed her to control.Property 1 is achieved by OpenFlow-enabled switches. In Amy’s experiment, the default action for all packets that don’t come from Amy’s PC could be to forward them through the normal processing pipeline. Amy’s own packets would be forwarded directly to the outgoing port, without being processed by the normal pipeline.Property 2 depends on the controller. The controller should be seen as a platform that enables researchers to implement various experiments, and the restrictions of Property 2 can be achieved with the appropriate use of permissions or other ways to limit the powers of individual researchers to control flow entries. The exact nature of these permission-like mechanisms will depend on how the controller is implemented. We expect that a variety of controllers will emerge. As an example of a concrete realization of a controller, some of the authors are working on a controller called NOX as a follow-on to the Ethane work [8]. A quite different controller might emerge by extending the GENI management software to OpenFlow networks.3.2 More ExamplesAs with any experimental platform, the set of experiments will exceed those we can think of up-front — most experiments in OpenFlow networks are yet to be thought of. Here, for illustration, we offer some examples of how OpenFlow-enabled networks could be used to experiment with new network applications and architectures.Example 1: Network Management and Access Con trol. We’ll use Ethane as our first example [7] as it was the research that inspired OpenFlow. In fact, an OpenFlow Switch can be thought of as a generalization of Ethane’s datapath switch. Ethane used a specific implementation of a controller, suited for network management and control, that manages the admittance and routing of flows. The basic idea of Ethane is to allow network managers to define a network-wide policy in the central controller, which is enforced directly by making admission control decisions for each new flow. A controller checks a new flow against a set of rules, such as “Guests can communicate using HTTP, but only via a web proxy” or “VoIP phones are not allowed to communicate with laptops.” A controller associates pack ets with their senders by managing all the bindings between names and addresses — it essentially takes over DNS, DHCP and authenticates all users when they join, keeping track of which switch port (or access point) they are connected to. One could envisage an extension to Ethane in which a policy dictates that particular flows are sent to a user’s process in a controller, hence allowing researcher-specific processing to be performed in the network.Example 2: VLANs. OpenFlow can easily provide users with their own isolated network, just as VLANs do. The simplest approach is to statically declare a set of flows which specify the ports accessible by traffic on a givenVLAN ID. Traffic identified as coming from a single user (for example, originating from specific switch ports or MAC addresses) is tagged by the switches (via an action) with the appropriate VLAN ID.A more dynamic approach might use a controller to manage authentication of users and use the knowledge of the users’ locations for tagging traffic at runtime.Example 3: Mobile wireless VOIP clients. For this example consider an experiment of a new call-handoff mechanism for WiFi-enabled phones. In the experiment VOIP clients establish a new connection over the OpenFlow-enabled network. A controller is implemented to track the location of clients, re-routing connections — by reprogramming the Flow Tables — as users move through the network, allowing seamless handoff from one access point to another.Example 4: A non-IP network. So far, our examples have assumed an IP network, but OpenFlow doesn’t require packets to be of any one format — so long as the Flow Table is able to match on the packet header. This would allow experiments using new naming, addressing and routing schemes. There are several ways an OpenFlow-enabled switch can support non-IP traffic. For example, flows could be identified using their Ethernet header (MAC src and dst addresses), a new EtherType value, or at the IP level, by a new IP Version number. More generally, we hope that future switches will allow a controller to create a generic mask (offset + value + mask), allowing packets to be processed in a researcher-specified way.Example 5: Processing packets rather than flows.The examples above are for experiments involving flows — where a controller makes decisions when the flow starts. There are, of course, interesting experiments to be performed that require every packet to be processed. For example, an intrusion detection system that inspects every packet, an explicit congestion control mechanism, or when modifying the contents of packets, such as when converting packets from one protocol format to another.Figure 3: Example of processing packets through anexternal line-rate packet-processing device, such as a programmable NetFPGA router.There are two basic ways to process packets in an OpenFlow-enabled network. First, and simplest, is to force all of a flow’s packets to pass through a controller. To do this, a controller doesn’t add a new flow ent ry into the Flow Switch — it just allows the switch to default to forwarding every packet to a controller. This has the advantage of flexibility, at the cost of performance. It might provide a useful way to test the functionality of a new protocol, but is unlikely to be of much interest for deployment in a large network.The second way to process packets is to route them to a programmable switch that does packet processing — for example, a NetFPGA-based programmable router. The advantage is that the packets can be processed at line-rate in a user-definable way; Figure 3 shows an example of how this could be done, in which the OpenFlow-enabled switch operates essentially as a patch-panel to allow the packets to reach the NetFPGA. In some cases, the NetFPGA board (a PCI board that plugs into a Linux PC) might be placed in the wiring closet alongside the OpenFlow-enabled switch, or (more likely) in a laboratory.4. THE OPENFLOW CONSORTIUMThe OpenFlow Consortium aims to popularize OpenFlow and maintain the OpenFl ow Switch Specification. The Con sortium is a group of researchers and network administrators at universities and colleges who believe their research mission will be enhanced if OpenFlow-enabled switches are installed in their network.Membership is open and free for anyone at a school, college, university, or government agency worldwide. The OpenFlow Consortium welcomes individual members who are not employed by companies that manufacture or sell Ethernet switches, routers or wireless access points (because we want to keep the consortium free of vendor influence). To join, send email to .The Consortium web-site contains the OpenFlow Switch Specification, a list of consortium members, and reference implementations of OpenFlow switches.Licensing Model: The OpenFlow Switch Specification is free for all commercial and non-commercial use. (The exact wording is on the web-site.)Commercial switches and routers claiming to be “OpenFlow-enabled” must conform to the requirements of an OpenFlow Type 0 Switch, as defined in the OpenFlow Switch Specification. OpenFlow is a trademark of Stanford University, and will be protected on behalf of the Consortium.5. DEPLOYING OPENFLOW SWITCHESWe believe there is an interesting market opportunity for network equipment vendors to sell OpenFlow-enabled switches to the research community. Every building in thousands of colleges and universities contains wiring closets with Ethernet switches and routers, and with wireless access points spread across campus.We are actively working with several switch and router manufacturers who are adding the OpenFlow feature to their products by implementing a Flow Table in existing hardware; i.e. no hardware change is needed. The switches run the Secure Channel software on their existing processor.We have found network equipment vendors to be very open to the idea of adding the OpenFlow feature. Most vendors would like to support the research community without having to expose the internal workings of their products. We are deploying large OpenFlow networks in the Computer Science and Electrical Engineering departments at Stanford University. The networks in two buildings will be replaced by switches running OpenFlow. Eventually, all traffic will run over the OpenFlow network, with production traffic and experimental traffic being isolated on different VLANs under the control of network administrators. Researchers will control their own traffic, and be able to add/remove flow-entries.。
心流状态的英语
心流状态的英语心流（Flow）是一种由心理学家米哈里·契克森米哈伊(Mihaly Csikszentmihalyi) 提出的概念，描述了在专注并投入某项活动时的心理状态，通常伴随着深度的满足感和沉浸感。
以下是关于心流状态的英语内容：Introduction:Flow is a psychological state characterized by intense focus and immersion in an activity, leading to a sense of energized involvement and satisfaction. Coined by psychologist Mihaly Csikszentmihalyi, the concept has been widely studied to understand the optimal experience individuals have when fully engaged in a task.Key Elements of Flow:1. Clear Goals:- The activity has well-defined goals that provide direction and purpose.2. Immediate Feedback:- Immediate and clear feedback is available, allowing individuals to adjust their actions in real-time.3. Balance of Skill and Challenge:- There is a harmony between the individual's skill level and the challenge presented by the activity, ensuring neither boredom nor overwhelming frustration.4. Complete Concentration:- Total concentration on the task at hand, leading to a distortion of time and an unawareness of external distractions.5. Loss of Self-Consciousness:- The sense of self disappears during the activity, and individuals become fully absorbed in what they are doing.6. Sense of Control:- Participants feel a sense of control over their actions, contributing to a heightened sense of mastery.Examples of Flow Activities:- Playing a musical instrument.- Engaging in sports or physical activities.- Writing or creating art.- Solving complex problems or puzzles.- Coding and programming.Benefits of Flow:- Enhanced performance and productivity.- Increased intrinsic motivation.- Positive emotional experiences.- Improved learning and skill development.Conclusion:Flow is a unique and desirable psychological state where individuals experience a harmonious blend of challenge, skill, and focus. Recognizing and cultivating flow experiences in various aspects of life can contribute to a more fulfilling and meaningful existence. Understanding the conditions that foster flow can help individuals optimize their engagement and satisfaction in diverse activities.。
关于action的英语谚语
关于action的英语谚语action的意思是行动、开始。
下面是店铺整理的关于action的英语谚语，欢迎大家阅读。
关于action的英语谚语摘抄A man , like a watch , is to be valued by his manner of going.Wlliam Penn, British admiral一个人，正如一个时钟，是以他的行动来定其价值的。
英国海军上将佩恩 W.Action is the last resource of those who know not how to dream.Oscar Wilde, British dramatis不善于想象的人一切乞求于行动。
英国剧作家王尔德 O .Action is consolatory. It is the enemy of thought and the friend of glittering illusions.Joseph Conrad, British novelist行动是令人安慰的，它是思想的敌人，是美好幻想的朋友。
英国小说家康拉得 . J .Action springs not from thought, but from a readiness forresponsibility.Dietrich Bonhoeffer, German theologian行动并不来自思想，而是来自愿意承担责任。
德国神学家邦赫费尔. D .Behavior is a mirror in which everyone shows his image.Johann Wolfgang von Goethe, German poet and dramatist 行为是一面镜子，每个人都把自己的形象显现于其中。
德国人、剧作家歌德 .J . W .Deeds are fruits, words are but leaves.Joseph Rlema Prake, American poet行动才是果实，言词不过是树叶。
Openflow-未来网络的基础协议(全文)
Openflow:未来络的基础协议(全文)2008年4月，一篇署名为NickMcKeown的论文《OpenFlow：enablinginnovationincampusnetworks》在ACMCommunicationsReview上发表。
至此，被美国斯坦福大学cleanslate研究组提出将近一年的Openflow向世人揭开了神秘面纱，一种将络转发与控制解耦的新型络交换模型逐渐浮出水面。
两年后，NickMcKeown又提出SDN（SoftwareDefineNetworks，软件定义络）的概念。
它起源于Openflow，也正是它，使Openflow引起业界重视，Openflow甚至在某种程度上成为SDN的代名词。
“SDN 是理念，Openflow是技术。
”盛科络CEO孙建勇一语道破SDN与Openflow之间的区别。
“在可以实现SDN的技术体系中，OpenFlow是相对成熟的技术之一。
”清华大学络研究院络体系结构与IPv6研究室主任毕军又指出了两者之间的关系。
虽然技术相对成熟，但是在追求标准化的IT界，尚未完全标准化的Openflow的标准化之路如何前行？这个过程会对SDN的发展起到什么样的作用？四个版本传统络架构由单独运行、封闭的设备连接构成，每台设备都有单独的操作系统，数据的转发和控制都由交换机和路由器完成，这会造成络的管控细节做得不是特别到位。
各种设备以及其相对孤立的操作系统在络中零散分布，也使络变得复杂且封闭。
此外，由于设备异构，络管理的兼容性也很难做到极致。
Openflow能够很好地解决以上问题。
与当今IT界追捧的“软硬件一体化”不同，SDN试图用软硬件分离的理念颠覆现有的络架构。
Openflow作为新一代络的核心技术，在分离软硬件方面肩负重任。
Openflow交换机以流表的方式进行数据的转发，FlowVisor负责对络进行虚拟化，控制器负责络控制，三者各司其职、分工明确而又相互配合，构成了Openflow的络架构。