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(2009-03-31 14:22:00)



Friday, January 9th, 2009 星期五, 2009年1月9日

Arouter is a networking device whose software and hardware are usuallytailored to the tasks of routing and forwarding information.路由器是网络设备的软件和硬件通常是针对任务路由和转发信息。 For example, on the Internet, information is directed to various paths by routers.例如,在互联网上的信息是针对不同的路径的路由器。

Routers connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router.路由器连接两个或多个逻辑子网,不一定地图一对一的物理接口的路由器。 Theterm “layer 3 switch” often is used interchangeably with router, butswitch is a general term without a rigorous technical definition.术语“第3层交换机” ,常常是交替使用的路由器,但开关是通用术语,没有一个严格的技术定义。 In marketing usage, it is generally optimized for Ethernet LAN interfaces and may not have other physical interface types.在市场营销中的使用,人们普遍优化以太网LAN接口,并不得有其他物理接口类型。 Incomparison a network hub does not do any routing, instead every packetit receives on one network line gets forwarded to the other networklines.相比之下网络枢纽并不做任何路由,而不是收到的每一个数据包在一个网络线路被转交给其他网络线路。

Routers operate in two different planes:路由器工作在两个不同的飞机:

*Control plane, in which the router learns the outgoing interface thatis most appropriate for forwarding specific packets to specificdestinations, *控制平面,在该路由器得知即将离任的接口,最适合于特定的数据包转发到特定的目的地,
*Forwarding plane, which is responsible for the actual process ofsending a packet received on a logical interface to an outbound logicalinterface. *转发平面,负责实际进程发送数据包收到的一个逻辑接口的输出的逻辑接口。

General information一般资料
Routersgenerally contain a specialized operating system (eg Cisco’s IOS orJuniper Networks JUNOS and JUNOSe or Extreme Networks XOS), RAM, NVRAM,flash memory, and one or more processors, as well as two or morenetwork interfaces.路由器通常包含了一个专门的作业系统(如思科IOS或Juniper网络公司的JUNOS和Extreme网络的JUNOSe或振荡器) ,内存, NVRAM ,快闪记忆体,以及一个或多个处理器,以及两个或两个以上的网络接口。 Except for multiple network interfaces this is typical of an embedded computer.除了多个网络接口,这是典型的嵌入式计算机。

High-endrouters contain many processors and specialized Application-specificintegrated circuits (ASICs) and do a great deal of parallel processing.高端路由器包含许多处理器和专门特定应用集成电路( ASIC )和做了大量的并行处理。 Chassisbased systems like the Nortel MERS-8600 or ERS-8600 routing switch,(pictured right) have multiple ASICs on every module and allow for awide variety of LAN, MAN, METRO, and WAN technology ports or other,customizable connections.底盘系统,如北电网络市场汇率- 8600或的ERS - 8600路由交换机, (右)有多个ASIC的每一个模块,并允许各种局域网,城域网,城域网和广域网技术或其他港口,可定制的连接。 Simpler routers are used where cost is more important and traffic is less, for example, in providing a home Internet service.简单的路由器是用来在更重要的是成本和交通较少,例如,在提供一个主页的互联网服务。 With the appropriate software (such as Untangle, SmoothWall, XORP or Quagga), an ordinary personal computer can become a router.与适当的软件(如解开,光面, XORP或Quagga ) ,普通的个人电脑可以成为路由器。

Control plane控制平面
Routers are like intersections whereas switches are like streets.路由器是一样的十字路口,而开关一样的街道。

Controlplane processing leads to the construction of what is variously calleda routing table or routing information base (RIB).控制平面处理导致建造什么是各种所谓的路由表或路由信息库证明( RIB ) 。 TheRIB may be used by the Forwarding Plane to look up the outboundinterface for a given packet, or, depending on the routerimplementation, the Control Plane may populate a separate forwardinginformation base (FIB) with destination information.肋骨可被转发平面查找出站接口为特定的数据包,或者根据路由器执行,控制平面可填入一个单独的转发信息库(纤维蛋白原)与目的地信息。 RIBsare optimized for efficient updating with control mechanisms such asrouting protocols, while FIBs are optimized for the fastest possiblelookup of the information needed to select the outbound interface.肋骨都经过了优化,高效率的更新与控制机制,如路由协议,同时得到了优化FIBs尽快查找所需的信息来选择出站接口。

TheControl Plane constructs the routing table from knowledge of theup/down status of its local interfaces, from hard-coded static routes,and from exchanging routing protocol information with other routers.构建的控制平面的路由表从知识的向上/向下的地位及其当地的接口,从硬编码的静态路由,交换和路由协议的信息与其他路由器。 Itis not compulsory for a router to use routing protocols to function, iffor example it was configured solely with static routes.这不是强制性的路由器使用路由协议功能,例如,如果有人只配置静态路由。 Therouting table stores the best routes to certain network destinations,the “routing metrics” associated with those routes, and the path to thenext hop router.路由表中存储的最佳途径,以某些网络目的地, “路由指标”与这些路线和路径下一跳路由器。

Routersdo maintain state on the routes in the RIB/routing table, but this isquite distinct from not maintaining state on individual packets thathave been forwarded.路由器做维护国家的路线,肋骨/路由表,但是这是完全不同于没有维护国家对个人的数据包已提交。

Forwarding plane (aka data plane)转发平面(又名数据平面)
Forthe pure Internet Protocol (IP) forwarding function, router designtries to minimize the state information kept on individual packets.纯互联网协议( IP )转发功能,路由器设计的尝试,以尽量减少国家对个人信息保密的数据包。 Once a packet is forwarded, the router should no longer retain statistical information about it.一旦一个数据包转发时,路由器不应该再保留的统计信息。 It is the sending and receiving endpoints that keeps information about such things as errored or missing packets.这是发送和接收终端,让信息像差错或丢失的数据包。

Forwarding decisions can involve decisions at layers other than the IP internetwork layer or OSI layer 3.转发决定可能涉及决策层以外的IP网络层或OSI的第三层。 Again, the marketing term switch can be applied to devices that have these capabilities.再次,营销长期开关可用于设备中,这些能力。 A function that forwards based on data link layer, or OSI layer 2, information, is properly called a bridge.一个函数的基础上向前数据链路层,或OSI的第二层,信息,就是所谓的正确的桥梁。 Marketing literature may call it a layer 2 switch, but a switch has no precise definition.营销文学可以称之为第二层交换机,但开关没有确切的定义。

Amongthe most important forwarding decisions is deciding what to do whencongestion occurs, ie, packets arrive at the router at a rate higherthan the router can process.其中最重要的转发决定是怎么做决定时发生拥挤,即数据包到达路由器的速率高于路由器可以处理。 Three policies commonly used in the Internet are Tail drop, Random early detection, and Weighted random early detection.三项政策中常用互联网尾下降,随机早期检测,并加权随机早期检测。 Taildrop is the simplest and most easily implemented; the router simplydrops packets once the length of the queue exceeds the size of thebuffers in the router.尾下降是最简单和最容易执行;路由器只需滴一次包的长度超过了队列的大小,缓冲区中的路由器。 Random early detection (RED) probabilistically drops datagrams early when the queue exceeds a configured size.随机早期检测(红色)概率下降数据早期当队列超过了配置的大小。 Weightedrandom early detection requires a weighted average queue size to exceedthe configured size, so that short bursts will not trigger random drops.加权随机早期检测需要一个加权平均队列大小超过所设定的大小,因此,短时间不会触发随机下降。


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