实验拓扑：
试验要求：R1通过FR分别与R2和R3相连，R2与R3之间没有连接，形成一个hub and spoke网络拓扑结构，要求R1 R2 R3都采用点对点子接口。
试验目的：掌握hub路由器与spoke路由器都采用点对点子接口的时候IP的分配与其他情况下IP的分配的差别。
试验配置：
R1：
R1(config)#int s1/0
R1(config-if)#enca fram
R1(config-if)#no shu
R1(config-if)#exit
R1(config)#int s1/0.1 point-to-point
R1(config-subif)#ip add 172.16.3.3 255.255.255.0
R1(config-subif)#fram interface-dlci 301
R1(config-fr-dlci)#exit
R1(config-subif)#exit
R1(config)#int s1/0.2 point-to-point
R1(config-subif)#ip add 172.16.1.3 255.255.255.0
R1(config-subif)#fram interface-dlci 302
R1(config-fr-dlci)#no shu
R1(config-subif)#exit
R2：
R2(config)#int s1/0
R2(config-if)#enca fram
R2(config-if)#no shu
R2(config-if)#exit
R2(config)#int s1/0.1 point-to-point
R2(config-subif)#ip add 172.16.3.1 255.255.255.0
R2(config-subif)#fram interface-dlci 103
R2(config-fr-dlci)#no shu
R2(config-subif)#exit
R3：
R3(config)#int s1/0
R3(config-if)#enca fram
R3(config-if)#no shu
R3(config-if)#exit
R3(config)#int s1/0.1 point-to-point
R3(config-subif)#ip add 172.16.1.1 255.255.255.0
R3(config-subif)#fram interface-dlci 203
R3(config-fr-dlci)#no shu
R3(config-subif)#exit
好了，要特别注意R1的两个子接口的IP配置，hub路由器点对点子接口的IP是不能够在同一网段的，切记！！！
下面在三台路由器上show fram map：
R1#show fram map
Serial1/0.1 (up): point-to-point dlci, dlci 301(0x12D,0x48D0), broadcast
status defined, active
Serial1/0.2 (up): point-to-point dlci, dlci 302(0x12E,0x48E0), broadcast
status defined, active
R2#show fram map
Serial1/0.1 (up): point-to-point dlci, dlci 103(0x67,0x1870), broadcast
status defined, active
R3#show fram map
Serial1/0.1 (up): point-to-point dlci, dlci 203(0xCB,0x30B0), broadcast
status defined, active
全部都active了，现在分别在R2和R3上ping R1的相应接口：
R2#ping 172.16.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.3.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 180/242/288 ms
R3#ping 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 100 percent (5/5), round-trip min/avg/max = 120/273/720 ms
好的，都可以ping通，那如果我在R3上去ping172.16.3.3会是什么结果呢？
R3#ping 172.16.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.3.3, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
无法ping通，让我们debug ip pac来看一下：
R3#debug ip pac
IP packet debugging is on
R3#ping 172.16.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.3.3, timeout is 2 seconds:
*Mar 1 00:03:35.247: IP: s=172.16.1.1 (local), d=172.16.3.3, len 100, unroutable.
*Mar 1 00:03:37.247: IP: s=172.16.1.1 (local), d=172.16.3.3, len 100, unroutable.
*Mar 1 00:03:39.247: IP: s=172.16.1.1 (local), d=172.16.3.3, len 100, unroutable.
*Mar 1 00:03:41.247: IP: s=172.16.1.1 (local), d=172.16.3.3, len 100, unroutable.
*Mar 1 00:03:43.247: IP: s=172.16.1.1 (local), d=172.16.3.3, len 100, unroutable.
Success rate is 0 percent (0/5)
出现unroutable，无法路由，因为不在同一网段，路由器需要查找路由表来进行转发，我们察看路由表可以看到并没有到172.16.3.0网段的路由，我们自己添加一条默认路由上去，下一跳指向172.16.1.3这个子接口，我们可以到R1上验证一下172.16.1.3能否到172.16.3.3：
R1#ping
Protocol [ip]:
Target IP address: 172.16.1.3
Repeat count [5]:
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: 172.16.3.3
Type of service [0]:
Set DF bit in IP header? [no]:
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.3, timeout is 2 seconds:
Packet sent with a source address of 172.16.3.3
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 288/326/384 ms
OK，没有问题，下面配置缺省路由：
R3(config)#ip route 0.0.0.0 0.0.0.0 172.16.1.3
同样R2也需要配置缺省路由：
R2(config)#ip route 0.0.0.0 0.0.0.0 172.16.3.3
好了，我们ping测试一下：
R2#ping 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 100 percent (5/5), round-trip min/avg/max = 144/176/192 ms
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:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 288/354/432 ms
都可以ping通。
实验总结：在hub and spoke拓扑结构中，如果hub路由器采用点对点子接口的话，每个点对点子接口配置的IP不能在同一个网段，在spoke路由器上还需要加上一条默认路由才可以与其他spoke路由器相互通讯。
写在最后：通过连载试验，我把Frame-relay在部分网格拓扑结构hub路由器与spoke路由器基本上所有用到的接口类型都演示了一遍，也演示了怎样让spoke路由器相互之间可以通信的方法，通过这几日的连载，大家应该可以掌握在Frame-relay部分网格拓扑结构中怎样配置hub和spoke路由器以适应不同的需求。希望大家能够喜欢！
本文转自loveme2351CTO博客，原文链接：http://blog.51cto.com/loveme23/43728 ，如需转载请自行联系原作者
