R1#show running-config Building configuration... ! ! hostname R1 ! aaa new-model aaa authentication login default local aaa authentication login NO_AUTHEN none aaa authentication ppp default if-needed local enable secret 5 <deleted> ! username admin password 7 <deleted> username R5 password 7 <deleted> ! ip subnet-zero no ip finger ! isdn switch-type basic-ni ! interface Loopback0 ip address 172.17.1.1 255.255.255.0 ! interface Ethernet0 ip address 172.16.1.1 255.255.255.0 ! interface Serial0 backup delay 10 30 backup interface BRI0 ip address 192.168.10.2 255.255.255.252 encapsulation ppp no ip mroute-cache no fair-queue ! interface BRI0 ip address 172.20.10.2 255.255.255.0 encapsulation ppp dialer idle-timeout 900 dialer map ip 172.20.10.1 name R5 broadcast 5551111 dialer map ip 172.20.10.1 name R5 broadcast 5551112 dialer load-threshold 1 outbound dialer-group 1 isdn switch-type basic-ni isdn spid1 51299699380101 9969938 isdn spid2 51299699460101 9969946 ppp authentication chap ppp multilink ! router ospf 5 log-adjacency-changes network 172.16.0.0 0.0.255.255 area 0 network 172.17.0.0 0.0.255.255 area 0 network 172.20.10.0 0.0.0.255 area 0 network 192.168.10.0 0.0.0.3 area 0 ! ip classless no ip http server ! access-list 101 remark Interesting traffic definition for backup link access-list 101 permit ip any any dialer-list 1 protocol ip list 101 R5#show running-config Building configuration... Current configuration: ! ! hostname R5 ! aaa new-model aaa authentication login default local aaa authentication login NO_AUTHEN none aaa authentication ppp default if-needed local enable secret 5 <deleted> ! username admin password 7 <deleted> username R1 password 7 <deleted> ! ip subnet-zero ! isdn switch-type basic-ni ! interface Loopback0 ip address 172.22.1.1 255.255.255.0 ! interface BRI1/0 ip address 172.20.10.1 255.255.255.0 encapsulation ppp dialer idle-timeout 900 dialer map ip 172.20.10.2 name R1 broadcast dialer-group 1 isdn switch-type basic-ni isdn spid1 51255511110101 5551111 isdn spid2 51255511120101 5551112 ppp authentication chap ppp multilink ! interface Serial2/0 ip address 192.168.10.1 255.255.255.252 encapsulation ppp no fair-queue clockrate 64000 ! ! router ospf 5 network 172.20.10.0 0.0.0.255 area 0 network 172.22.1.0 0.0.0.255 area 0 network 192.168.10.0 0.0.0.3 area 0 ! ip classless no ip http server ! dialer-list 1 protocol ip any

NOTE

Remember that shutting down the primary interface administratively via the shutdown command will not bring up the backup link. You need to physically unplug the cables to verify the configuration's success.

After the backup link is activated, the OSPF table is exchanged, and the new routes using the backup link are installed. The traffic now flows across the backup link. Example 6-12 shows the results of the backup link operation.

R1#show ip route Gateway of last resort is not set 172.17.0.0/24 is subnetted, 1 subnets C 172.17.1.0 is directly connected, Loopback0 172.16.0.0/24 is subnetted, 1 subnets C 172.16.1.0 is directly connected, Ethernet0 172.20.0.0/16 is variably subnetted, 2 subnets, 2 masks C 172.20.10.0/24 is directly connected, BRI0 C 172.20.10.1/32 is directly connected, BRI0 172.22.0.0/32 is subnetted, 1 subnets O 172.22.1.1 [110/1563] via 172.20.10.1, 00:00:22, BRI0 R1#show interface BRI 0 BRI0 is up, line protocol is up Hardware is BRI with U interface and external S bus interface Internet address is 172.20.10.2, subnet mask is 255.255.255.0 MTU 1500 bytes, BW 256 Kbit, DLY 100000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation PPP, loopback not set DTR is pulsed for 5 seconds on reset LCP Open, multilink Open Open: IPCP

Practical Exercise 6-2 Solution

Example 6-11. Configuration Output

Example 6-12. Verifying the Backup Link Functionality