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1、 2003, Cisco Systems, Inc. All rights reserved. 2003, Cisco Systems, Inc. All rights reserved.2 付业茂 CCIE(#9556) Tel：(0755)83651433 Mail: Ncutsy.futyl- Routing Protocol 高度总结 2003, Cisco Systems, Inc. All rights reserved.3 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-4 Routing protocols are
2、 used between routers to determine paths and maintain routing tables. 路由器学习路径的方式 Once the path is determined, a router can route a routed protocol. 数据包的运输工具 Routing Protocol & Routed Protocol 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-5 在TCP/IP协议栈中，Routed Protocol（IP）工 作在网络层，而Routing Pr
3、otocol工作在传输层或 者应用层，他们之间的关系为：Routing Protocol 负责学习最佳路径，而Routed Protocol根据最佳 路径将来自上层的信息封装在IP包里传输 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-6 Protocols, Ports, and Reliability 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-7 Static Route Uses a route that a network administrator
4、enters into the router manually Dynamic Route Uses a route that a network routing protocol adjusts automatically for topology or traffic changes Identifying Static and Dynamic Routes 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-8 Defines a path to an IP destination network or subnet or ho
5、st Router(config)#ip route network mask address | interfacedistance permanent Static Route Configuration 仅仅在点到点（point-to-point）链路上才可以指定本地的转发端口； Distance指的是AD，指定Next-Hop时缺省为1，指定本地转发端口时 缺省为0。 通过修改缺省的Distance可以实现浮动的静态路由起备份的作用 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-9 Static Route Exampl
6、e This is a unidirectional route. You must have a route configured in the opposite direction. 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-10 Floating Static RoutesFloating Static Routes 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-11 Default Routes This route allows the stub n
7、etwork to reach all known networks beyond router A. 在Stub Router（连接Stub Network的路由器）上通常配置缺省 路由，这也是大多数企业在接入INTERNET时所采用的配置。 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-12 Classful and Classless 路由协议从不同的角度可以进行不同 的分类。 根据协议在更新时是否携带掩码分为 Classless和Classful两大类。 2003, Cisco Systems, Inc. All rig
8、hts reserved.BSCI 2.02-13 Classful路由协议 Classful路由协议在路由更新时不携带掩码 Classful路由协议只能支持定长子网掩码（FLSM） 同一个大类网络下的子网信息当掩码长度一致时可以相互穿越。掩码长度 不一致时子网信息不能传递。 Classful路由协议不支持非连续的子网（Discontiguous subnet） 子网信息穿过另外一个大类网络时将在网络边界做自动汇总（10.2.0.0和 10.3.0.0进入路由器C时被自动汇总为10.0.0.0，这样在C上会产生路由混乱） 在TCP/IP协议中，RIPv1以及 IGRP 属于Classful路由
9、协议。 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-14 Classless路由协议 Classless路由协议在路由更新时携带掩码 Classless路由协议能支持变长子网掩码（VLSM） Classless路由协议可以支持非连续的子网（Discontiguous subnet） 10.2.0.0/16 192.168.1.32/30192.168.1.16/28 10.3.0.0/16 10.2.0.0/16 192.168.1.16/28 192.168.1.32/30 10.3.0.0/16 10.2.0.0/16 1
10、92.168.1.16/28 192.168.1.32/30 10.3.0.0/16 10.2.0.0/16 192.168.1.32/30 192.168.1.16/28 10.3.0.0/16 在TCP/IP协议中，RIPv2以及 EIGRP OSPF BGP 属于Classless路由协议。 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-15 Classful Lookup & Longest Match Lookup 路由器收到数据包以后，会根据数据包中目的地址到 路由表中查找相应的路由条目，如果找到相匹配的路 由就会按
11、照该路由处理数据包，否则在缺省情况下会 扔弃数据包（策略路由PBR在没有普通路由的情况下 也可以处理数据包） 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-16 Interpreting the IP Routing Table with a Classful Protocol p1r3# show ip route Gateway of last resort is 0.0.0.0 to network 0.0.0.0 10.0.0.0/24 is subnetted, 3 subnets, R 10.1.1.0/24 120
12、/1 via 10.1.2.2, 00:00:05, Ethernet0 C 10.1.2.0/24 is directly connected, Ethernet0 R 10.1.3.0/24 120/2 via 10.1.2.2, 00:00:05, Ethernet0 R 192.168.24.0/24 120/2 via 10.1.2.2, 00:00:16, Ethernet0 R 172.16.0.0/16 120/3 via 10.1.2.2, 00:00:16, Ethernet0 R* 0.0.0.0/0 120/3 via 10.1.2.2, 00:00:05, Ether
13、net0 Where will the router send traffic bound for the following destinations? 192.168.24.3 172.16.5.1 10.1.2.7 200.100.50.0 10.2.2.2 缺省情况下，目的地为10.2.2.2的数据包将会被丢弃，因为它属于A类地址，路由器有两条10的路由，缺省 情况下运行CLASSFUL协议的路由器会认为它学到了该网络的所有子网，所以会把它扔掉（IP CLASSLESS可以解决此问题） 2003, Cisco Systems, Inc. All rights reserved.BSCI
14、 2.02-17 The IP Classless Command Router(config)# ip classless Replaces the default behavior of classful routing protocols to match against only known subnets of a major network Changes default behavior of classful routing protocol for unknown subnets On by default in Cisco IOS version 12.0 and late
15、r Has no effect on most classless routing protocols because they use the longest-match criteria by default Longestmatch：routers using longestmatch criteria make routing decisions by matching the most number of bits possible in the destination network 2003, Cisco Systems, Inc. All rights reserved.BSC
16、I 2.02-18 路由汇总的好处：1 减少路由表条目的数量从而节省内存及CPU资源 2 可以使得路由变化的影响本地化（Localize） Classful路由协议只支持自动汇总 Classless路由协议支持手动汇总 缺省情况下，RIPv2，EIGRP以及BGP做自动汇总（no auto-summary关闭 自动汇总）。 做汇总的路由器将自动产生一条目的地为汇总地址指向NULL0的路由以避免 路由环路及路由黑洞。 路由汇总 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-19 路由汇总 2003, Cisco Systems, Inc. All rights reserved.BSCI 2.02-20 NULL0路由避免路由环路
