Section 3: ISDN (4 Points)

• If your Frame Relay network fails, allow R4 to dial into R1. Use passwords that are difficult to detect. Ensure R4 dials out after 5 seconds of Frame Relay failure. If the Frame Relay network restores, keep the call connected for a further 45 seconds before disconnecting. OSPF is required over the ISDN network when a call is established. Do not configure any Layer 3 addressing on the physical ISDN interfaces.

You only have one option here and you are given plenty of clues; you need to use the backup interface solution with the delay configured to meet the timing requirements. You only need to configure a backup interface on R4 as R1 is not required to dial into R4; therefore you can simply omit a dialer string on R1. Because OSPF is required over the link, it will need to be enabled on the ISDN network; it will not establish the link until the Frame Relay network fails. The Layer 3 addressing and PPP CHAP can simply be configured on a dialer interface as opposed to the physical BRI; they are joined by dialer pool statements. The command no peer neighbor-route is configured on the dialer interfaces to remove the /32 host route that would otherwise be present when the ISDN network is established. If you have configured this correctly as shown in Example 3-29 and Example 3-30, you have scored 4 points.

Example 3-29. R1 ISDN Backup Configuration

 username R4 password 0 cisco ! interface BRI0/0  no ip address  encapsulation ppp  dialer pool-member 1  isdn switch-type basic-net3 ! interface Dialer0  ip address 10.10.10.1 255.255.255.240  encapsulation ppp no peer neighbor-route  dialer pool 1  dialer-group 1  ppp authentication chap ! dialer-list 1 protocol ip permit 

Example 3-30. R4 ISDN Backup Configuration

 username R1 password 0 cisco ! interface BRI0/0  no ip address  encapsulation ppp  dialer pool-member 1  isdn switch-type basic-net3 ! interface Serial0/0  backup delay 5 45  backup interface Dialer0 ! interface Dialer0  ip address 10.10.10.2 255.255.255.240  encapsulation ppp  no peer neighbor-route  dialer pool 1  dialer string 1111  dialer-group 1  ppp authentication chap ! dialer-list 1 protocol ip permit 

NOTE

The backup commands are entered under the Frame Relay interface s0/0 on R4. To test the backup disconnect, simply shut down the corresponding interface on the Frame Relay switch from R4 instead of shutting down the interface on R4, because this will not work.

Example 3-31 shows the backup process when the Frame Relay switch is disconnected from R4 using the debug dialer command.

Example 3-31. R4 Backup Process

 R4#debug dialer Dial on demand events debugging is on R4# R4# 01:16:19: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to down 01:16:19: %LINK-3-UPDOWN: Interface Serial0/0, changed state to down 01:16:19: %OSPF-5-ADJCHG: Process 1, Nbr 10.1.1.1 on Serial0/0 from 2WAY to DOWN , Neighbor Down: Interface down or detached 01:16:19: %OSPF-5-ADJCHG: Process 1, Nbr 10.6.6.6 on Serial0/0 from 2WAY to DOWN, N eighbor Down: Interface down or detached 01:16:20: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to down 01:16:24: Di0 DDR is shutdown, could not clear interface. 01:16:24: BR0/0 DDR: rotor dialout [best] 01:16:24: BR0/0 DDR: Dialing cause ip (s=10.10.10.2, d=224.0.0.5) 01:16:24: BR0/0 DDR: Attempting to dial 1111 01:16:24: BR0/0:2: interface must be fifo queue, force fifo 01:16:24: %LINK-3-UPDOWN: Interface BRI0/0:1, changed state to up 01:16:24: BR0/0:1: interface must be fifo queue, force fifo 01:16:24: %DIALER-6-BIND: Interface BR0/0:1 bound to profile Di0 01:16:24: BR0/0:1 DDR: dialer protocol up 01:16:24: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0/0:1, changed state to up 01:16:29: %ISDN-6-CONNECT: Interface BRI0/0:1 is now connected to 1111 R1 01:16:31: %OSPF-5-ADJCHG: Process 1, Nbr 10.1.1.1 on Dialer0 from LOADING to FULL, Loading Done 

Example 3-32 shows the backup process restoring to Frame Relay after the Frame Relay switch has been reconnected to R4note the timing intervals.

Example 3-32. R4 Backup Restoration

 R4# 01:18:01: %LINK-3-UPDOWN: Interface Serial0/0, changed state to up 01:18:02: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed   state to up 01:18:46: BR0/0:1 DDR: disconnecting call 01:18:46: Di0 DDR: dialer shutdown complete 01:18:46: Di0 DDR: No bundle in dialer_fsm_up 01:18:197568495616: %ISDN-6-DISCONNECT: Interface BRI0/0:1   disconnected from 1111 R1, call lasted 143 seconds 01:18:46: %OSPF-5-ADJCHG: Process 1, Nbr 10.1.1.1 on Dialer0 from FULL to DOWN, Neighbor Down: Interface down or detached 01:18:46: %LINK-3-UPDOWN: Interface BRI0/0:1, changed state to down 01:18:46: BR0/0 DDR: has total 0 call(s), dial_out 0, dial_in 0 01:18:46: BR0/0:1 DDR: disconnecting call 01:18:46: %DIALER-6-UNBIND: Interface BR0/0:1 unbound from profile Di0 01:18:47: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0/0:1,   changed state to down 01:18:48: %LINK-5-CHANGED: Interface Dialer0, changed state to standby mode