Router2。其中采用PPP/CHAP做安全认证，在 Router1中应建立一个用户，以对端路由器主机名作为用户名，即用户名应为Router2。同时在Router2中应建立一个用户，以对端路由器主机名作为用户名，即用户名应为Router1。所建的这两用户的password必须相同。 相关命令如下： 任务 命令
设置路由器与modem的接口指令 chat-s cript s cript-name EXPECT SEND EXPECT SEND (etc.)
设置端口在挂断前的等待时间 dialer idle-timeout seconds
设置协议地址与电话号码的映射 dialer map protocol next-hop-address [name hostname] [broadcast] [modem-s cript modem-regexp] [system-s cript system-regexp] [dial-string]
设置电话号码 dialer string dial-string
指定在特定线路下路由器默认 使用的chat-s cript s cript {dialer|reset} s cript-name Router1:
hostname Router1 !
enable secret 5 $1$QKI7$wXjpFqC74vDAyKBUMallw/ !
username Router2 password cisco
chat-s cript cisco-default \\\c !
interface Ethernet0
ip address 10.0.0.1 255.255.255.0 !
interface Async1
ip address 192.200.10.1 255.255.255.0 encapsulation ppp async default routing async mode dedicated dialer in-band dialer idle-timeout 60
dialer map ip 192.200.10.2 name Router2 modem-s cript cisco-default 573 dialer-group 1
ppp authentication chap !
ip route 10.0.1.0 255.255.255.0 192.200.10.2 dialer-list 1 protocol ip permit !
line con 0 line aux 0 modem InOut
modem autoconfigure discovery flowcontrol hardware
Router2:
hostname Router2 !
enable secret 5 $1$F6EV$5U8puzNt2/o9g.t56PXHo. !
username Router1 password cisco !
interface Ethernet0
ip address 10.0.1.1 255.255.255.0 !
interface Async1
ip address 192.200.10.2 255.255.255.0 encapsulation ppp async default routing async mode dedicated dialer in-band dialer idle-timeout 60
dialer map ip 192.200.10.1 name Router1 dialer-group 1
ppp authentication chap !
ip route 10.0.0.0 255.255.255.0 192.200.10.1 dialer-list 1 protocol ip permit !
line con 0 line aux 0 modem InOut
modem autoconfigure discovery flowcontrol hardware !
相关调试命令： debug dialer
debug ppp authentication debug ppp error debug ppp negotiation debug ppp packet show dialer
3. 异步拨号备份DDN专线：
此例主连接采用DDN专线，备份线路为电话拨号。当DDN专线连接正常时，主端口S0状态为up，line protocol亦为up,则备份线路状态为standby，line protocol为down，此时所有通信均通过主接口进行。当主接口连接发生故障时，端口状态为down，则激活备份接口，完成数据通信。此方法不适合为X.25做备份。因为，配置封装为X.25的接口只要和X.25交换机之间的连接正常其接口及line protocol的状态亦为 up,它并不考虑其它地方需与之通信的路由器的状态如何，所以若本地路由器状态正常，而对方路由器连接即使发生故障，本地也不会激
活备份线路。例4将会描述如何为X.25做拨号备份。 以下是相关命令： 任务 命令
指定主线路改变后，次线路状态发生改变的延迟时间 backup delay {enable-delay | never} {disable-delay | never}
指定一个接口作为备份接口 backup interface type number hostname c2522rb !
enable secret 5 $1$J5vn$ceYDe2FwPhrZi6qsIIz6g0 enable password cisco !
username c4700 password 0 cisco ip subnet-zero
chat-s cript cisco-default \\\c
chat-s cript reset atz !
interface Ethernet0
ip address 16.122.51.254 255.255.255.0 no ip mroute-cache !
interface Serial0 backup delay 10 10 backup interface Serial2
ip address 16.250.123.18 255.255.255.252 no ip mroute-cache no fair-queue !
interface Serial1 no ip address no ip mroute-cache shutdown !
interface Serial2 physical-layer async
ip address 16.249.123.18 255.255.255.252 encapsulation ppp async mode dedicated dialer in-band dialer idle-timeout 60
dialer map ip 16.249.123.17 name c4700 6825179 dialer-group 1
ppp authentication chap !
interface Serial3 no ip address shutdown no cdp enable !
interface Serial4 no ip address shutdown no cdp enable !
interface Serial5 no ip address no ip mroute-cache shutdown !
interface Serial6 no ip address no ip mroute-cache shutdown !
interface Serial7 no ip address no ip mroute-cache shutdown !
interface Serial8 no ip address no ip mroute-cache shutdown !
interface Serial9 no ip address no ip mroute-cache shutdown !
interface BRI0 no ip address no ip mroute-cache shutdown !
router eigrp 200 network 16.0.0.0 !
ip classless
!
dialer-list 1 protocol ip permit !
line con 0 line 2
s cript dialer cisco-default s cript reset reset modem InOut
modem autoconfigure discovery rxspeed 38400 txspeed 38400 flowcontrol hardware line aux 0 line vty 0 4 password cisco login ! end c2522rb#
4. 异步拨号备份X.25:
设置X.25的拨号备份,首先X.25连接的端口必须运行动态路由协议,异步拨号口必须使用静态路由.本例选择EIGRP作为路由选择协议,将静态路由的 Metric的值设置为200,由于EIGRP的默认Metric为90,所以当同时有两条路径通往同一网段时,其中Metric值小的路径生效,而当 X.25连接出现问题时,路由器无法通过路由协议学习到路由表，则此时静态路由生效，访问通过拨号端口实现。当X.25连接恢复正常时，路由器又可以学习到路由表，则由于 Metric值的不同，静态路由自动被动态路由所代替，这样就实现了备份的功能。 路由器Router1配置如下: hostname router1 !
enable secret 5 $1$UTvD$99YiY2XsRMxHudcYeHn.Y. enable password cisco !
username router2 password cisco ip subnet-zero
chat-s cript cisco-default \\\c
chat-s cript reset atz interface Ethernet0
ip address 202.96.38.100 255.255.255.0 !
interface Serial0
ip address 202.96.0.1 255.255.255.0 encapsulation x25 x25 address 10112227