本实验通过设置浮动静态路由，可以实现ISDN拨号备份。浮动静态路由即静态预定义运行代价（COST）。
备份思想是当主线路出现故障，高COST的静态路由开始起作用，产生一个ISDN呼叫。
当主线路恢复时，将断开这条高Cost的路由，重新起用原线路。
配置实例 R3
Building configuration...
Current configuration : 1025 bytes
!
version 12.1
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname R3
!
enable secret 5 $1$VgNb$9fc/n4VziCOMvalJ.az6M0
enable password cisco
!
username R5 password 0 cisco
!
!
!
!
ip subnet-zero
no ip finger
no ip domain-lookup
!
isdn switch-type basic-net3
!
!
!
interface Ethernet0
ip address 195.1.1.1 255.255.255.0
no keepalive
!
interface Serial0
ip address 193.1.1.1 255.255.255.0
encapsulation ppp
clockrate 500000
!
interface Serial1
no ip address
shutdown
!
interface BRI0
ip address 196.1.1.1 255.255.255.0
encapsulation ppp
dialer idle-timeout 90
dialer map ip 196.1.1.2 name R5 38846302
dialer load-threshold 1 outbound
dialer-group 1
isdn switch-type basic-net3
ppp authentication chap
ppp multilink
!
router rip
network 193.1.1.0
network 195.1.1.0
!
ip classless
ip route 0.0.0.0 0.0.0.0 196.1.1.2 121
ip http server
!
dialer-list 1 protocol ip permit
!
line con 0
transport input none
line aux 0
line vty 0 4
password cisco
login
!
end
配置实例 R5
Building configuration...
Current configuration : 910 bytes
!
version 12.1
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname R5
!
enable secret 5 $1$vD0X$8U3bwtxlBsXdu9Y45OGs01
enable password cisco
!
username R3 password 0 cisco
!
!
!
!
ip subnet-zero
no ip finger
no ip domain-lookup
!
isdn switch-type basic-net3
!
!
!
interface Ethernet0
ip address 197.1.1.1 255.255.255.0
no keepalive
!
interface Serial0
ip address 193.1.1.2 255.255.255.0
encapsulation ppp
!
interface Serial1
no ip address
shutdown
!
interface BRI0
ip address 196.1.1.2 255.255.255.0
encapsulation ppp
dialer map ip 196.1.1.1 name R3 38846301
dialer-group 1
isdn switch-type basic-net3
ppp authentication chap
ppp multilink
!
router rip
network 193.1.1.0
network 197.1.1.0
!
ip classless
ip http server
!
dialer-list 1 protocol ip permit
!
line con 0
transport input none
line aux 0
line vty 0 4
password cisco
login
!
end[/HIDE}