You have two methods of providing Layer 3 ISDN backup, Dialer Watch and an OSPF Demand circuit. As you have not been provided with which networks in particular require backing up, you have to configure the Demand circuit. When you configure an OSPF demand circuit, you should be aware that any topology change will cause your ISDN circuit to become active so you must ensure you have a stable network; otherwise, your line will constantly be connected. You configure only one end of the link with the ip ospf demand-circuit command and this should be placed on R1 as the question states that R1 should initiate the call. You can, therefore, configure R4 without a number to dial R1 so R4 never dials R1. Example 2-38 shows R1 with the ISDN line disconnected and still maintaining a full neighbor adjacency with R4 over the ISDN; Example 2-39 shows R4 in the same state. Example 2-38. R1 OSPF Demand StatusR1#sh isdn act -------------------------------------------------------------------------------- ISDN ACTIVE CALLS -------------------------------------------------------------------------------- Call Calling Called Remote Seconds Seconds Seconds Charges Type Number Number Name Used Left Idle Units/Currency -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- R1#sh ip ospf neigh Neighbor ID Pri State Dead Time Address Interface 10.4.4.4 1 FULL/ - 00:00:34 10.100.100.3 Virtual-Access1 10.4.4.4 1 FULL/ - - 10.10.10.2 BRI0/0 Example 2-39. R4 OSPF Demand StatusR4#sh isdn act -------------------------------------------------------------------------------- ISDN ACTIVE CALLS -------------------------------------------------------------------------------- Call Calling Called Remote Seconds Seconds Seconds Charges Type Number Number Name Used Left Idle Units/Currency -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- R4#sh ip ospf neigh Neighbor ID Pri State Dead Time Address Interface 10.1.1.1 1 FULL/ - 00:00:31 10.100.100.1 Virtual-Access1 10.200.200.5 1 FULL/ - 00:00:37 10.100.101.2 Virtual-Access2 10.1.1.1 1 FULL/ - - 10.10.10.1 BRI0/0 It is good practice to configure PPP circuits with the command no peer neighbor-route to remove the /32 host route that is added to the routing table when a PPP link becomes active. You might find that when your ISDN line disconnects, this route will be removed from the routing table and cause an OPSF topology change; this will cause your ISDN line to re-establish. You should have already configured the peer route option on your virtual templates on R1 and R4 earlier within the OSPF section to remove the host routes. As requested in the question, you must use CHAP authentication; you should already have username and passwords configured for the PPP over Frame Relay section so simply enable ppp authentication chap on the ISDN interfaces of R1 and R4. Do not forget to add authentication to the ISDN network as itis part of OSPF area 0. If you have configured this correctly as shown in Example 2-40 and Example 2-41, you have scored 4 points. Example 2-40. R1 ISDN Configurationusername R4 password 0 cisco ! interface BRI0/0 ip address 10.10.10.1 255.255.255.240 encapsulation ppp ip ospf message-digest-key 1 md5 james ip ospf demand-circuit dialer map ip 10.10.10.2 name R4 broadcast 2222 dialer-group 1 isdn switch-type basic-net3 no peer neighbor-route ppp authentication chap ! dialer-list 1 protocol ip permit Example 2-41. R4 ISDN Configurationusername R1 password 0 cisco ! interface BRI0/0 ip address 10.10.10.2 255.255.255.240 encapsulation ppp ip ospf message-digest-key 1 md5 james dialer map ip 10.10.10.1 name R1 broadcast dialer-group 1 isdn switch-type basic-net3 no peer neighbor-route ppp authentication chap ! dialer-list 1 protocol ip permit |