第1段:测试基本的连通性 Term_Server#1 [Resuming connection I to R1 ...] R1#ping 10.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.1.1.2, timeout is 2 seconds: !!!!! SUCcess rate is 100 percent (5/5), round-trip min/avg/max = 4/4/4 ms Ripping 172.16.1.3 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.1.3, timeout is 2 seconds: .!!!! Success rate is 80 percent (4/5), round-trip min/avg/max = 4/4/4 ms R1# (键入ctrl+shift+6,x,切换回终端服务器) Term_Server#2 [Resuming connection 2 to R2 ... ]
R2#ping 172.16.1.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds: ..... R2#sh ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, 0 - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route
Gateway of last resort is not set 第2段:加入静态路由并测试连通性 R2#conft Enter configuration commands, one per line. End with CNTL/Z, R2(config)#ip route 172.16.1.0 255.255.255.0 10.1.1.1 R2(config)#end R2#sh ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, 0 - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U- per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set
172.16.0.0/24 is subnetted, 1 subnets S 172.16.1.0[1/0]via 10.1.0.1 10.0.0.0/24 is subnetted,1subnets C 10.1.1.0 is directly connected, EthernetO R2#ping 172.16.1.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds: HW R2#ping 172.16.1.3 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos 10172.16.1.3, timeout is 2 seconds: ..... success rate is 0 percent(0/5) R2# (键入ctrl+shift+6,x,切换回终端服务器) Term_Server#3 [Resuming connection 3 to R3 ... ] R3#conft Enter configuration commands, one per line. End with CNTL/Z. R3(config)#ip route 10.1.1.0 255.255.255.0 172.16.1.1 R3(config)#^Z R3#ping 10.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms R3# R3#sh ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP externa1, 0 -OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, LI - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 1 subnets C 172.16.1.0 is directly connected, EthernetO 10.0.0.0/24 is subnetted, 1 subnets S 10.1.1.0[1/0]via 172.16.1.1 . R3# Term_Server#1 [Resuming connection I to R1 ... ] R1#sh ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, 0 - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, LI - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/24 is subnetted,1 subnets C 172.16.1.0 is directly connected Ethernet0 10.0.0.0/24 is subnetted,1 subnets C 10.1.1.0 is directly connected Ethernet0 R1# (键入ctrl+shift+6, x切换回终端服务器) Term_Server#2 [Resuming connection 2 to R2 ... ] R2#sh ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, 0 - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, LI - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route
Gateway of last resort is not set
S 172.16.0.0/24 is subnetted, 1 subnets 10.0.0.0/24 is subnetted, 1 subnets C 10.1.1.0 is directly connected, Ethernet0 R2# (键入ctrl+shift+6, x切换回终端服器) 第3段:使用trace命令 Term_Server#3 [Resuming connection 3 to R3 ... ] R3#trace 10.1.1.2 Type escape sequence to abort. Tracing the route to 10.1.1.2 1 172.16.1.14msec 4 msec 4 msec 2 10.1.1.24msec 4 msec* R3# (键入ctrl+shift+6, x切换回终端服务器) 第4段:禁用IP路由功能 Term_Server#1 [Resuming connection I to R1 ... ] R1#conft Enter configuration commands, one per line. End with CNTL/Z. R1(config)#no ip routing R1(config)# R1#sh ip route Default gateway is not set
Host Gateway Last Use Total Uses Interface ICMP R1# (键入ctrl+shift+6,x切回换回终端服务器) Term_Server#3 [Resuming connection 3 to R3 ... ]
R3#ping 172.16.1.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds: .!!!! Success rate. ia 80 percent (4/5), round-trip min/avg/max=4/5/8ms R3#ping 10.1.1.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds: !!!!! Successrateis 100 percent(5/5>,round-trip min/avg/max=4/4/4ms R3#ping 10.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.1.1.2, timeout is 2 seconds: Success rate is 0 percent(0/5) R3# (1)配置好各路由器的以太网接口地址后，在R1上用ping命令测试各网段内部的连通性。结果表明，R1到R2、R1到R3在IP层是正常连通的。 (2)接下来转到R2路由器上，在R2上ping172.16.1.1，即R1的E1接口地址，这是跨网段的ping，可以看到，没有ping通。 (3)在R2上执行show ip route命令查看其路由表，结果显示只有直接相连的网段10.1.1.0/24在其路由表内，标志为"C"，即connected。 (4)在R2上加入1条静态路由: ip route 172.16.1.0 255.255.255.0 10.1.1.1 这个语句的意思是:从本路由器出发，发往172.16.1.0 0 255.255.255.0网段的数据包，其下一跳点(Next Hop)的地址是10.1.1.1(即R1的E0接口地址)。 (5)在R2上配置好静态路由后，查看其路由表，结果显示刚刚加入的静态路由己经生效了。该路由表项前的"S"表示是静态(static)路由，中括号内的"1/10"表示这条路由的治理距离是1，度量值是0。这两个概念将在后续的实验中多次看到并加以说明。 (6)在R2上再次Ping172.16.1.1，成功;但是Ping与172.16.1.1处于同一个网段的172.16.1.3 (R3)则不成功。 上述结果的解释为: 在R2路由器上配置了到网段172.16.1.0/24的静态路由后，从R2发出的ICMP Echo包可以到达R1和R3路由器。R1路由器路由表内有到10.1.1.0/24网段的路由(直接相连)，而R3、路由器则没有相应的路由表项。结果是R1可以发送ICMP Echo Reply包到10.1.1.2，而R3则不能发送ICMP Echo Reply包到1O.1.1.2，原因是没有到10.1.1.0/24网段的路由。 可能有一些喜欢深究问题的读者会问:你凭什么作如此解释，为什么不可以是从R1发出的ICMP包没有到达R3造成的ping不通R3? 我们可以用路由器上的监测结果来说明这个问题。 在R3上发出命令debug ip packet和debug ip icmp，来监测IP包和ICMP包的传输情况，得到的监测结果如下: 03:17:44:IP:s=10.1.1.2(Ethernet0)，d=172.16.1.3(Ethernet0)，len 100，rcvd3 03:17:44:ECMR echo reply sent，srcl72.16.1.3，dst 10.1.1.2 03:17:44:IP:s=172.16.1.3(local)，d=10.1.12，len 100，unroutable 03:17:46:IP:s=10.1.1.2(Ethernet0)，d=172.16.1.3(Ethernet0)，len 100，rcvd3 03:17:46:ICMR echo reply sent，src 172.16.1.3，dst 10.1.1.2 03:17:46:IP:s=172.16.1.3(local),d=10.1.1.2,len 100,unroutable 以上监测结果表明:R3收到了来自R1的ICMP Echo包，源地址为10.1.1.2，目的地址为172.16.1.3;然后试图发送ICMP Echo reply包到10.1.1.2(R1)，但是由于不可路由(即结果中的"unroutable")的原因，此IP包被丢弃，没有从R3路由器的任何接口上送出，从而造成R1不能接收到ICMP的应答包，导致Ping测试失败。 (7)使用trace命令可以显示IP包在传输的过程中的每一个跳点的IP地址，从而查看IP包所经过的整个路径。 (8)路由器的缺省配置是启动IP路由 即可以路由IP包。在第4段中，我们用no ip routing命令关闭了R1路由器的IP路由功能，然后发了3个ping指令，目的地址分别为172.16.1.1、10.1.1.1和10.1.1.2。可以看到前两个Ping是成功的，最后一个则失败。我们有必要记住这一结果，它表明了在禁用IP路由的情况下什么是可达，什么不可达。请注重在Ping指令发出之前用show ip route命令后的显示结果。
