三、配置过程： hostname R_A interface Serial2/0 ip address 192.168.1.1 255.255.255.0 encapsulation ppp ppp pap sent-username R_A password 0 123 clock rate 64000 R_A(config-if)#ip address 192.168.1.1 255.255.255.0 R_A(config-if)#no shutdown %LINK-5-CHANGED: Interface Serial2/0， changed state to up Router>en Router#conf t Enter configuration commands， one per line. End with CNTL/Z. Router(config)#hostname R_B R_B(config)#username R_A password 0 123 R_B(config)#interface s3/0 R_B(config-if)#encapsulation ppp R_B(config-if)#ppp authentication pap R_B(config-if)#ip address 192.168.1.2 255.255.255.0 R_B(config-if)#no shutdown 在路由器R_A上： R_A#debug ppp authentication PPP authentication debugging is on Serial2/0 Using hostname from interface PAP Serial2/0 Using password from interface PAP Serial2/0 PAP: O AUTH-REQ id 17 len 15 Serial2/0 PAP: Phase is FORWARDING， Attempting Forward %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial2/0， changed state to up 在路由器R_B上： R_B#ping 192.168.1.1 Type escape sequence to abort. Sending 5， 100-byte ICMP Echos to 192.168.1.1， timeout is 2 seconds: Success rate is 100 percent (5/5)， round-trip min/avg/max = 2/4/6 ms 最后我们需要注意用户名、密码信息与路由器的对应关系；认证端、被认证端之间的信息对应关系；认证信息大小写敏感；修改配置后，若未生效，尝试重启端口。
