ip网络技术基础-路由协议详解_计算机硬件及网络_it计

路由协议基础,内容,路由协议基本介绍静态路由协议及动态路由协议路由协议分类常用路由协议,概念,Internet ： inter + network路由器( router ): route + er 路由协议 : routing protocol,概念,地址 ： 10.10.10.10 /24路由表： 10.10.10.0/24 via 10.10.9.1AS ： Autonomous system,To route, a router needs to do the following:Know the destination addressIdentify the sources it can learn fromDiscover possible routesSelect the best routeMaintain and verify routing information,What Is Routing?,Routers must learn destinations that are not directly connected.,What Is Routing? (Cont.),路由,Static DefaultDynamic （1） 信息的传播 （2） 路由的计算,Static RouteUses a route that a network administrator enters into the router manually,Dynamic RouteUses a route that a network routing protocol adjusts automatically for topology or traffic changes,Identifying Static and Dynamic Routes,Static Routes,Configure unidirectional static routes to and from a stub network to allow communications to occur.,Static Route Example,This is a unidirectional route. You must have a route configured in the opposite direction.,Default Routes,This route allows the stub network to reach all known networks beyond router A.,路由协议种类,按应用范围分: IGP :Interior gateway protocol EGP:exterior gateway protocol按作用原理分: 距离矢量: distance vector 链路状态: link - state,An autonomous system is a collection of networks under a common administrative domain.IGPs operate within an autonomous system.EGPs connect different autonomous systems.,Autonomous Systems: Interior or Exterior Routing Protocols,Administrative Distance: Ranking Routes,距离矢量路由协议,初始化时，所有路由器在本机形成与本地直接连接的链路记录路由器向所有相连的路由器广播路由表内已有的记录路由器向外广播接收到的路由信息，再在邻路由器形成记录,相关内容,路由更新： 定期更新路由计算： hop 或复合路由收敛：缺点： 收敛慢、路由回环、路由表全部更新优化措施：毒性翻转、 水平分割、触发更新增强型距离矢量协议,典型协议,RIPIGRPEIGRP,链路状态路由协议,当路由器初始化或当网络结构发生变化时，路由器会产生链路状态广播数据包LSA（Link-State Advertisement）所有路由器会通过一种被称为刷新（Flooding）的方法来交换链路状态数据。路由协议收敛以后，所有的路由器会根据其各自的链路状态信息数据库计算出各自的路由表。,相关内容,SPF算法层次结构Metric,典型协议,OSPFIS-IS,After initial flood, pass small event-triggered link-state updates to all other routers,Link-State Routing Protocols,Minimizes routing table entriesLocalizes impact of a topology change within an area,Link-State Network Hierarchy Example,Link-State Routing Protocol Algorithms,Benefits of Link-State Routing,Fast convergence: changes are reported immediately by the source affected.Robustness against routing loops:Routers know the topology. Link-state packets are sequenced and acknowledged. By careful (hierarchical) network design, you can utilize resources optimally.,Drawbacks to Link-State Routing Protocols,Initial discovery may cause flooding.Memory- and processor-intensive.,距离矢量VS链路状态,距离矢量路由协议： share information locally use a distributed route calculation 链路状态路由协议: information distributed unchanged ; each router perform a local best-path calculation,BGP协议,Border Gateway Protocol广泛应用于目前Internet上路径矢量IBGP ，EBGP路由对等体策略,Autonomous Systems,Autonomous System 65000,Autonomous System 65500,IGPs: RIP, IGRP, OSPF, EIGRP,EGPs: BGP,An autonomous system (AS) is a collection of networks under a single technical administrationIGPs operate within an autonomous systemEGPs connect different autonomous systems,BGP Is Used Between Autonomous Systems,BGP is used between autonomous systemsGuarantees exchange of loop-free routing information,BGP,B,BGP,AS65500,AS65250,BGP,AS64520,AS65000,A,B,C,F,E,D,Routing Table Prefixes 020501104,027,BGP Characteristics,BGP is a distance vector protocol with enhancements:Reliable updatesBGP runs on top of TCP (port 179)Incremental, triggered updates onlyPeriodic keepalives to verify TCP connectivityRich metrics (called path vectors or attributes)Designed to scale to huge internetworks (for example, the Internet),BGP in IP Packets,BGP is an advanced distance vector routing protocolRelies on TCP for reliable session managementUses TCP port number 179,TCP Header,Port No.,SegmentPayload,IP Header,Protocol Number,Frame Header,CRC,Packet Payload,Frame Payload,6TCP17UDP,179BGP23Telnet25SMTP,Tables,IGPRoutingProtocol,BGPRoutingProtocol,IP,BGP,BGP has its own table, in addition to the IP routing tableInformation can be exchanged between the two tables,Any two routers that have formed a TCP connection in order to exchange BGP routing information are called peers or neighbors,Peers = Neighbors,AS 65000,Neighbors,AS 65500,Neighbors,A,C,B,Internal BGP,When BGP neighbors belong to the same AS it is called internal BGP (IBGP)Neighbors do not have to be directly connected,External BGP,When BGP neighbors belong to different autonomous systems it is called external BGP (EBGP)Neighbors should be directly connected,A,AS 65000,AS 65500,EBGP Neighbors,IBGP Neighbors,C,B,Policy-Based Routing,BGP allows administrators to define policies, or rules, for how data will flow through the autonomous systems,BGP Attributes,BGP attributes include:AS-pathNext-hopLocal preferenceMulti-exit discriminator (MED)OriginCommunity,BGP defines the following message types:OpenIncludes holdtime and BGP router IDKeepaliveUpdateInformation for one path only (could be to multiple networks)Includes path attributes and networksNotificationWhen error detectedBGP connection closed after sent,BGP Message Types,Route Selection Decision Process,Consider only (synchronized) routes with no AS loops and a valid next hop, and then:Prefer highest weight (local to router)Prefer highest local preference (global within AS)Prefer route originated by the local routerPrefer shortest AS-pathPrefer lowest origin code (IGP EGP incomplete)Prefer lowest MED (from other AS)Prefer EBGP path over IBGP pathPrefer the path through the closest IGP neighborPrefer oldest route for EBGP pathsPrefer the path with the lowest neighbor BG