网络环境：中心两台26xx路由器，分别用两条ISDN PRI连接到ISP，分支点一台Cisco1721路由器配置两块ISDN BRI接口分别拨号到中心的两台路由器上，这两条ISDN线路互为备份。
测试结果：主链路Down掉后备份线路启动拨号，10秒钟内网络重新连通。
配置如下：
中心路由器（主）：
2600#sh run
Building configuration...
Current configuration : 1180 bytes
!
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service passWord-encryption
!
hostname 2600
!
enable secret 5 $1$mCl2$fgVWoODbMwYUFTm1bAmFT/
!
username 1700_1 password 0 cisco
username 1700_2 password 0 cisco
ip subnet-zero
!
!
no ip domain-lookup
!
isdn switch-type primary-net5
!
controller E1 1/0
pri-group timeslots 1-31
!
controller E1 1/1
!
!
!
interface Loopback0
ip address 192.168.14.1 255.255.255.0
!
interface FastEthernet0/0
ip address 192.168.4.2 255.255.255.0
no keepalive
duplex auto
speed auto
standby 26 ip 192.168.4.5
standby 26 priority 150
standby 26 preempt
!
interface Serial1/0:15
ip address 10.1.1.5 255.255.255.0
encapsulation ppp
ip ospf network point-to-multipoint
ip ospf cost 10
ip ospf hello-interval 1
dialer-group 1
isdn switch-type primary-net5
ppp authentication chap
ppp multilink
!
router ospf 100
log-adjacency-changes
network 10.1.0.0 0.0.255.255 area 10
network 192.168.4.0 0.0.0.255 area 10
network 192.168.14.0 0.0.0.255 area 10
!
ip classless
ip http server
ip pim bidir-enable
!
!
dialer-list 1 protocol ip permit
!
line con 0
line aux 0
line vty 0 4
password zxn10
login
!
!
end
2600#
---------------------------------------------------------------------------------------------
中心路由器（备份）：
2600_1#sh run
Building configuration...
Current configuration : 1178 bytes
!
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname 2600_1
!
enable secret 5 $1$f8OA$J54DJebjWCXNj842VjF5P.
!
username 1700_2 password 0 cisco
username 1700_1 password 0 cisco
ip subnet-zero
!
!
no ip domain-lookup
!
isdn switch-type primary-net5
!
controller E1 1/0
pri-group timeslots 1-31
!
controller E1 1/1
!
!
!
interface Loopback0
ip address 192.168.14.2 255.255.255.0
!
interface FastEthernet0/0
ip address 192.168.4.3 255.255.255.0
no keepalive
duplex auto
speed auto
standby 26 ip 192.168.4.5
standby 26 preempt
!
interface Serial1/0:15
ip address 10.1.2.2 255.255.255.0
encapsulation ppp
ip ospf network point-to-multipoint
ip ospf hello-interval 1
dialer-group 1
isdn switch-type primary-net5
ppp authentication chap
ppp multilink
!
router ospf 100
log-adjacency-changes
network 10.1.2.0 0.0.0.255 area 10
network 192.168.4.0 0.0.0.255 area 10
network 192.168.14.0 0.0.0.255 area 10
!
router ospf 10
log-adjacency-changes
!
ip classless
ip http server
ip pim bidir-enable
!
!
dialer-list 1 protocol ip permit
!
line con 0
line aux 0
line vty 0 4
password zxn10
login
!
!
end
2600_1#
-----------------------------------------------------------------------------------------------------------
分支点路由器：
1700_1#wr t
Building configuration...
Current configuration : 1646 bytes
!
version 12.3
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname 1700_1
!
enable secret 5 $1$9vMy$9EKtTyavLLm4EerK1AWBf/
!
username 2600 password 0 cisco
username 2600_1 password 0 cisco
memory-size iomem 25
no aaa new-model
ip subnet-zero
!
!
!
isdn switch-type basic-net3
no scripting tcl init
no scripting tcl encdir
!
!
!
!
interface Loopback0
ip address 192.168.13.1 255.255.255.0
!
interface BRI0
bandwidth 128000
ip address 10.1.1.1 255.255.255.0
encapsulation ppp
ip ospf network point-to-multipoint
ip ospf hello-interval 1
dialer idle-timeout 0
dialer map ip 10.1.1.5 name 2600 broadcast 456000
dialer map ip 192.168.4.0 name 2600 broadcast 4561000
dialer load-threshold 1 either
dialer-group 1
isdn switch-type basic-net3
ppp authentication chap
ppp multilink
!
interface BRI1
ip address 10.1.2.1 255.255.255.0
encapsulation ppp
ip ospf network point-to-multipoint
ip ospf hello-interval 1
ip ospf demand-circuit
dialer map ip 10.1.2.2 name 2600_1 broadcast 4561001
dialer map ip 192.168.4.0 name 2600_1 broadcast 4561001
dialer load-threshold 1 either
dialer-group 2
isdn switch-type basic-net3
ppp authentication chap
ppp multilink
!
interface FastEthernet0
ip address 192.168.3.2 255.255.255.0
no ip redirects
speed auto
!
router ospf 100
log-adjacency-changes
network 10.1.0.0 0.0.255.255 area 10
network 192.168.3.0 0.0.0.255 area 10
network 192.168.13.0 0.0.0.255 area 10
!
ip classless
no ip http server
!
dialer-list 1 protocol ip permit
dialer-list 2 protocol ip permit
!
line con 0
line aux 0
line vty 0 4
password zxn10
login
!
!
end