4.2 PPP基本配置
实验目的：
1、掌握PPP基本配置。
2、理解PPP封装格式。
实验拓扑：
实验步骤：
1、依据图中拓扑，为R1和R2的串口链路部署PPP封装和IP地址，配置如下：
R1上
R1(config)#int s0/0
R1(config-if)#no shutdown
R1(config-if)#encapsulation ppp
R1(config-if)#ip address 12.1.1.1 255.255.255.0
R1(config-if)#exit
R2上
R2(config)#int s0/0
R2(config-if)#no shutdown
R2(config-if)#encapsulation ppp
R2(config-if)#ip address 12.1.1.2 255.255.255.0
R2(config-if)#exit
2、查看接口封装情况，并测试直连连通性。
R1#show interfaces s0/0
Serial0/0 is up, line protocol is up
Hardware is M4T
Internet address is 12.1.1.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation PPP, LCP Open
Open: IPCP, CDPCP, crc 16, loopback not set
Keepalive set (10 sec)
Restart-Delay is 0 secs
Last input 00:00:25, output 00:00:08, output hang never
Last clearing of "show interface" counters 00:01:09
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/1/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
Available Bandwidth 1158 kilobits/sec
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
25 packets input, 1394 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
26 packets output, 1699 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 output buffer failures, 0 output buffers swapped out
1 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up
可以看到，路由器采用PPP协议进行封装，并且接口处于正常状态，在R1上Ping R2，如下：
R1#ping 12.1.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 12.1.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/25/40 ms
此时，通过PPP封装后，直连连通性正常。
3、查看PPP封装格式，如下：
相比HDLC协议，PPP协议支持更多的功能，例如多协议支持、身份认证、链路捆绑等，并且兼容不同厂商，是更为优秀的广域网封装协议。此实验完成。
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