必威体育精装版CCNA课件3链路状态路由协议.ppt

? 2007 Cisco Systems, Inc. All rights reserved. ICND2 v1.0—2-* ? 2007 Cisco Systems, Inc. All rights reserved. ICND2 v1.0—2-* Introducing Link-State and Balanced Hybrid Routing Medium-Sized Routed Network Construction Outline Overview How Routing Information is Maintained with Link State Link-State Routing Protocol Algorithms Benefits and Limitations of Link-State Routing When to Use Link-State Routing Protocols Balanced Hybrid Routing Summary Link-State Routing Protocols After an initial flood of LSAs, link-state routers pass small, event-triggered link-state updates to all other routers. LS与DV对比的优势: 拓扑发生变化时,收敛快. 发送定期更新的频率低. 网络可以以层次方式划分区域,缩小路由变更范围. (OSPF,ISIS) 支持无类编址. 支持路由汇总. OSPF Hierarchical Routing autonomous systems由骨干区域area0和普通区域组成 区域化的网络减少路由更新的流量泛洪. Stub末梢区域 Totally Stub绝对末梢区域 NSSA次末梢区域 Totally NSSA绝对次末梢区域 Link-State Routing Protocol Algorithms Distance Vector and Link-State Protocols Comparison 对整个网络拓扑的了解 计算路由的算法 （1）距离矢量：能使路由器知道一个IP网络在网络里的哪个方向,并要经 过多少跳； （2）链路状态：路由是从拓扑表里计算出来 路由更新 Rip v1 广播更新,周期性更新,发整张路由表 OSPF eigrp 增量更新,组播更新,触发更新 Benefits of Link-State Routing 链状态协议根据成本（cost)来选择最优路径 通过使用触发更新，链路状态协议能够将网络拓扑变化立刻发送给网络中受影响的所有路由器，从而缩短了收敛时间 由于每台路由器都有完整的网络描述信息，因此不容易形成路由选择环路 通过细心地设计网络，可最大限度地减少链路状态数据库的规模，从而减少SPF计算量，提高会聚速度 Drawbacks of Link-State Routing 链路状态协议有路由选择表、拓扑表和邻居表，如果在大型的网络中，可能需要占用大量的内存 SPF在计算最佳路径时需要占用CPU周期，如果网络较大或复杂，需要占用大量的CPU资源 为了避免占用过多的内存和CPU资源，必须采用严格的层次型设计方案 启动时需要一定的时间才能转发数据包。（邻接） Balanced Hybrid Routing--EIGRP Shares attributes of both distance vector and link-state routing * * * Purpose: This figure introduces the link-state routing algorithm, the second of the classes of routing protocols, and outlines how it operates. Emphasize: In contrast with the analogy about the distance vector information being like individual road signs that show distance, link-state information is somewhat analogous to a road map with a “you are here” pointer showing the map reader’s current location. This larger perspective indicates the shortest p