先说点题外话，本来这两天是没时间来更新博客了的，但是事情出了点变化，使得我又有时间上网了，上网当然要到博客里面去逛逛了，没想到收到一封来自51cto的短信，说我的博客已经被评为推荐博客了，呵呵，真的很高兴能得到这样的荣誉，51cto让我感受到了学习的乐趣和写博客的动力（之前在csdn很没动力），更重要的是，能和这么多的网络技术爱好者共同学习，实在是一件很美妙的事情。感谢51cto。
最近我的这几篇关于cisco基础实验的文章都有幸得到了推荐，从网友的回复看，大多数网友还是支持我的，虽然我的文章对一部分博友来说很初级，但他们都没有说，相反还得到了他们的多次指点，真的很谢谢他们。当然我相信，我不会永远做初级的实验的，我是按照进度来循序渐进的进行的，总会做到高级一点的实验的，呵呵，当然，今天的实验应该还算初级的，呵呵。下面看实验。 实验开始前先说说Loopback接口，它是应用最为广泛的一种虚接口（即是接口不会依赖物理接口，接口的状态永远是UP的），网管完成网络规划之后，为了方便管理，会为每一台路由器创建一个loopback 接口，并在该接口上单独指定一个IP 地址作为管理地址，管理员会使用该地址对路由器远程登录（telnet）。因此学习它的配置还是有一定的意义的。 拓扑图如上所示，今天的实验通过show 的方式来展现，一来比较简短，二来比较易于察看，一目了然。1.1 在r1上show run：r1#show run Building configuration... Version 12.1 service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname r1 ! ! ! ip subnet-zero ! ! ! ! ! ! ! ! ! ! interface Loopback ip address 10.1.1.1 255.255.255.0 no ip directed broadcast ! interface Serial0 ip address 192.168.2.1 255.255.255.0 no ip directed-broadcast clock rate 64000 ! interface Ethernet0 ip address 192.168.1.2 255.255.255.0 no ip directed-broadcast ! ! router rip network 192.168.1.0 network 192.168.2.0 network 10.0.0.0 //我的loopback接口的IP地址为10.1.1.1 ! ip classless no ip http server ! ! ! line con 0 transport input none line aux 0 line vty 0 4/启用了vty线路方可进行telnet login password cisco ! no scheduler allocate end
r1# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 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, * - candidate default U - per-user static route C 192.168.1.0 is directly connected, Ethernet0 10.0.0.0/24 is subnetted, 1 subnets C 10.1.1.0 is directly connected, Loopback 192.168.2.0/24 is subnetted, 1 subnets C 192.168.2.0 is directly connected, Serial0 192.168.3.0/24 is subnetted, 1 subnets R 192.168.3.0 [120/1] via 192.168.2.2, 00:01:25, Serial0 //这个英文比较简单，应该看得懂 Routing Protocol is "rip" Sending updates every 30 seconds, next due in 7 seconds Invalid after 180 seconds, hold down 180, flushed after 240 //从这句可以得知：该配置采用rip协议，路由器每隔30s发出更新信息，（next due in 7 seconds？），超过180s未收到路由更新则认为该路由无效，如果经过240s还没收到更新信息，这该路由信息将会从路由表中删除。 Outgoing update filter list for all interfaces is Incoming update filter list for all interfaces is Redistributing: rip Default version control: send version 1, receive any version Interface Send Recv Key-chain Serial0 1 1 2 Ethernet0 1 1 2 Routing for Networks: 192.168.1.0 192.168.2.0 10.0.0.0 Routing Information Sources: 192.168.2.2 120 00:00:09 Distance: (default is 120) //rip的管理距离默认为120，该值越小越好 Building configuration... Version 12.1 service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname r2 ! ! ! ip subnet-zero ! ! ! ! ! ! ! ! ! ! interface Serial0 ip address 192.168.2.2 255.255.255.0 no ip directed-broadcast ! interface Ethernet0 ip address 192.168.3.1 255.255.255.0 no ip directed-broadcast ! ! router rip network 192.168.3.0 network 192.168.2.0 ! ip classless no ip http server ! ! ! line con 0 transport input none line aux 0 line vty 0 4 ! no scheduler allocate end Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 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, * - candidate default U - per-user static route C 192.168.2.0 is directly connected, Serial0 192.168.3.0/24 is subnetted, 1 subnets C 192.168.3.0 is directly connected, Ethernet0 192.168.1.0/24 is subnetted, 1 subnets R 192.168.1.0 [120/1] via 192.168.2.1, 00:08:16, Serial0 10.0.0.0/24 is subnetted, 1 subnets R 10.1.1.0 [120/1] via 192.168.2.1, 00:02:14, Serial0 Routing Protocol is "rip" Sending updates every 30 seconds, next due in 4 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is Incoming update filter list for all interfaces is Redistributing: rip Default version control: send version 1, receive any version Interface Send Recv Key-chain Serial0 1 1 2 Ethernet0 1 1 2 Routing for Networks: 192.168.3.0 192.168.2.0 Routing Information Sources: 192.168.2.1 120 00:00:03 Distance: (default is 120) //意思同r1中的意思 如图所示，在输入telnet 10.1.1.1 并回车之后，会要求输入密码，此处为cisco，输入之后便可以在pc1上对r1进行配置。
