双点双向重分布路由环路的产生.doc

双点双向重分布路由环路的产生左边运行OSPF协议，右边运行RIPV2协议，首先在R2上进行双向重分布，再在R3上进行路由重分布。基本配置省略。R2(config-router)#redistribute rip metric 10 subnetsR2(config-router)#redistribute ospf 1 metric 4R3上进行相同配置；R2#sh ip rou 34.0.0.0/24 is subnetted, 1 subnetsO E2 34.34.34.0 110/10 via 12.12.12.1, 01:45:24, Serial0/0 1.0.0.0/32 is subnetted, 1 subnetsO 1.1.1.1 110/65 via 12.12.12.1, 01:45:24, Serial0/0 5.0.0.0/32 is subnetted, 1 subnetsR 5.5.5.5 120/2 via 24.24.24.4, 00:00:26, Serial0/1 24.0.0.0/24 is subnetted, 1 subnetsC 24.24.24.0 is directly connected, Serial0/1 12.0.0.0/24 is subnetted, 1 subnetsC 12.12.12.0 is directly connected, Serial0/0 13.0.0.0/24 is subnetted, 1 subnetsO 13.13.13.0 110/128 via 12.12.12.1, 01:45:26, Serial0/0 45.0.0.0/24 is subnetted, 1 subnetsR 45.45.45.0 120/1 via 24.24.24.4, 00:00:01, Serial0/1R3#sh ip rou 34.0.0.0/24 is subnetted, 1 subnetsC 34.34.34.0 is directly connected, Serial0/1 1.0.0.0/32 is subnetted, 1 subnetsO 1.1.1.1 110/65 via 13.13.13.1, 01:46:10, Serial0/0 5.0.0.0/32 is subnetted, 1 subnetsO E2 5.5.5.5 110/10 via 13.13.13.1, 01:46:10, Serial0/0 24.0.0.0/24 is subnetted, 1 subnetsO E2 24.24.24.0 110/10 via 13.13.13.1, 01:46:10, Serial0/0 12.0.0.0/24 is subnetted, 1 subnetsO 12.12.12.0 110/128 via 13.13.13.1, 01:46:10, Serial0/0 13.0.0.0/24 is subnetted, 1 subnetsC 13.13.13.0 is directly connected, Serial0/0 45.0.0.0/24 is subnetted, 1 subnetsO E2 45.45.45.0 110/10 via 13.13.13.1, 01:46:13, Serial0/0会看到，在R3上5.5.5.5这条路由条目的下一跳指向了13.13.13.1，即指向了R1，其路由类型为O E2，也就是从OSPF内学到。当我们追踪到5.5.5.5的报文转发过程时，会发现绕了一圈，才到达5.5.5.5R3#traceroute 5.5.5.5Type escape sequence to abort.Tracing the route to 5.5.5.5 1 13.13.13.1 84 msec 36 msec 36 msec 2 12.12.12.2 80 msec 44 msec 40 msec 3 24.24.24.4 40 msec 72 msec 24 msec 4 45.45.45.5 84 msec * 64 msec-分析：为什么会产生这个问题？AD值。首先在R2上进行双向重分布时，R2会把5.5.5.5这个路由条目传递到OSPF路由协议区域，此条目的优先级就是110，R1收到这个条目也会把它传递给R3；这样R3由R1得到一条5.5.5.5路由条目，又由RIP路由协议区域内得到一条路由条目，其优先级为120。比较