Section 4: ISDN (6 Points) | CCIE Routing and Switching Practice Labs

Configure ISDN on R3 and R5 using PPP. R3 and R5 should be able to ping each other across the ISDN link.

If you configured this correctly as shown in Example 4-31, you have scored 3 points.

Make sure that only when the ISDN link is up that it will pass routing protocol across the link.
The ISDN link should pass routing protocol only when R5-s0/1 and/or R5-fa0/0 and/or R5-fa0/1 is down. Consider that the routing protocol can pass through the ISDN link when topology changes happen.

If you configured this correctly as shown in Example 4-31 and Example 4-32, you have scored 3 points.

The key to configuring as requested is to avoid the ISDN to advertise or pass traffic through the link when the other physical interfaces on R5 are up. Notice in the show command output what is basic to accomplish these requirements. Commands such as no cdp enable and no peer neighbor-route help to prevent unnecessary protocols' packets from exchanging information through the IDN link. The ip ospf demand-circuit command helps to avoid OSPF Hellos from being sent through the ISDN link; however, when a topology change occurs, R5 will send information through the ISDN link.

Example 4-31. R3 and R5 ISDN Configuration

 R3# ! username R5 password 0 cisco R3#sh run int bri0/0 Building configuration... Current configuration : 265 bytes ! interface BRI0/0  ip address 160.10.15.3 255.255.255.0  encapsulation ppp  ip ospf demand-circuit  dialer map ip 160.10.15.5 name R5 broadcast 2222  dialer-group 1  isdn switch-type basic-5ess  no peer neighbor-route  no cdp enable  ppp authentication chap end ! dialer-list 1 protocol ip permit ! R3# ! R5# ! username R5 password 0 cisco ! R5#sh run int bri0/0 Building configuration... Current configuration : 265 bytes ! interface BRI0/0  ip address 160.10.15.5 255.255.255.0  encapsulation ppp  ip ospf demand-circuit  dialer map ip 160.10.15.3 name R3 broadcast 1111  dialer-group 1  isdn switch-type basic-5ess  no peer neighbor-route  no cdp enable  ppp authentication chap end R5# R5#ping 160.10.15.3 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 160.10.15.3, timeout is 2 seconds: 2w3d: %LINK-3-UPDOWN: Interface BRI0/0:1, changed state to up..!!! Success rate is 60 percent (3/5), round-trip min/avg/max = 32/33/36 ms R5# 2w3d: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0/0:1, changed state to up 2w3d: %ISDN-6-CONNECT: Interface BRI0/0:1 is now connected to 1111 R3

The output in Example 4-32 shows the behavior of a backup environment using ISDN. Example 4-32 also shows the steps that were used to test it. Notice the highlighted notes and marks.

Example 4-32. R5 Routing Backup Output

 !  Notice on R5 the routes comig from the Serial S0/1 R5#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area        * - candidate default, U - per-user static route, o - ODR        P - periodic downloaded static route Gateway of last resort is not set      50.0.0.0/24 is subnetted, 1 subnets O E2    50.5.5.0 [110/100] via 160.10.37.2, 02:39:35, Serial0/1      140.200.0.0/24 is subnetted, 1 subnets O E2    140.200.10.0 [110/1] via 160.10.37.2, 02:35:48, Serial0/1 O E2 193.118.9.0/24 [110/100] via 160.10.37.2, 02:39:35, Serial0/1 O E2 20.0.0.0/8 [110/1] via 160.10.37.2, 02:29:08, Serial0/1 O E2 193.118.8.0/24 [110/100] via 160.10.37.2, 02:39:35, Serial0/1 O E2 193.118.10.0/24 [110/100] via 160.10.37.2, 02:39:35, Serial0/1 O E2 193.118.5.0/24 [110/100] via 160.10.37.2, 02:39:36, Serial0/1 O E2 193.118.4.0/24 [110/100] via 160.10.37.2, 02:39:36, Serial0/1      160.10.0.0/16 is variably subnetted, 16 subnets, 2 masks O IA    160.10.32.0/24 [110/112] via 160.10.37.2, 02:39:46, Serial0/1 O IA    160.10.33.0/24 [110/113] via 160.10.37.2, 02:39:46, Serial0/1 O       160.10.37.4/32 [110/112] via 160.10.37.2, 02:39:47, Serial0/1 O       160.10.37.2/32 [110/64] via 160.10.37.2, 02:39:47, Serial0/1 O       160.10.37.1/32 [110/112] via 160.10.37.2, 02:39:47, Serial0/1 C       160.10.37.0/24 is directly connected, Serial0/1 O IA    160.10.11.0/24 [110/122] via 160.10.37.2, 02:39:47, Serial0/1 C       160.10.15.0/24 is directly connected, BRI0/0 O       160.10.2.0/24 [110/65] via 160.10.37.2, 02:39:47, Serial0/1 O IA    160.10.3.0/24 [110/113] via 160.10.37.2, 02:39:47, Serial0/1 O       160.10.1.0/24 [110/113] via 160.10.37.2, 02:39:47, Serial0/1 O       160.10.6.0/24 [110/2] via 160.10.22.6, 2d00h, FastEthernet0/0 O       160.10.4.0/24 [110/113] via 160.10.37.2, 02:39:47, Serial0/1 C       160.10.5.0/24 is directly connected, Loopback0 C       160.10.25.0/24 is directly connected, FastEthernet0/1 C       160.10.22.0/24 is directly connected, FastEthernet0/0 O E2 193.118.7.0/24 [110/100] via 160.10.37.2, 02:39:37, Serial0/1      40.0.0.0/24 is subnetted, 1 subnets O E2    40.4.4.0 [110/100] via 160.10.37.2, 02:39:39, Serial0/1      130.200.0.0/24 is subnetted, 1 subnets O E2    130.200.10.0 [110/100] via 160.10.37.2, 02:39:39, Serial0/1 O E2 193.118.6.0/24 [110/100] via 160.10.37.2, 02:39:39, Serial0/1 O E2 193.118.1.0/24 [110/100] via 160.10.37.2, 02:39:39, Serial0/1 O E2 193.118.3.0/24 [110/100] via 160.10.37.2, 02:39:39, Serial0/1 O E2 193.118.2.0/24 [110/100] via 160.10.37.2, 02:39:39, Serial0/1 R5# R5# ! Here we are shuting down R5-Fa0/0 to test the contingency R5# R5#conf t Enter configuration commands, one per line.  End with CNTL/Z. R5(config)#int fa0/0 R5(config-if)#shut R5(config-if)# 2w3d: %OSPF-5-ADJCHG: Process 1, Nbr 160.10.6.6 on FastEthernet0/0 from FULL to   DOWN, Neighbor Down: Interface down or detached 2w3d: %OSPF-5-ADJCHG: Process 1, Nbr 160.10.3.3 on FastEthernet0/0 from FULL to   DOWN, Neighbor Down: Interface down or detached 2w3d: %LINK-3-UPDOWN: Interface BRI0/0:1, changed state to up 2w3d: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0/0:1, changed state to up 2w3d: %LINK-5-CHANGED: Interface FastEthernet0/0, changed state to   administratively down 2w3d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed   state to down R5(config-if)# R5(config-if)# R5(config-if)#int fa0/0 2w3d: %ISDN-6-CONNECT: Interface BRI0/0:1 is now connected to 1111 R5 R5(config-if)#int fa0/1 R5(config-if)#shut R5(config-if)# 2w3d: %OSPF-5-ADJCHG: Process 1, Nbr 160.10.1.1 on FastEthernet0/1 from FULL   to DOWN, Neighbor Down: Interface down or detached 2w3d: %LINK-5-CHANGED: Interface FastEthernet0/1, changed state to   administratively down 2w3d: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed   state to down R5(config-if)# R5(config-if)#int s0/1 R5(config-if)#shut R5(config-if)# 2w3d: %OSPF-5-ADJCHG: Process 1, Nbr 160.10.2.2 on Serial0/1 from FULL to DOWN,   Neighbor Down: Interface down or detached R5(config-if)# 2w3d: %LINK-5-CHANGED: Interface Serial0/1, changed state to administratively down 2w3d: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/1, changed state   to down R5(config-if)# R5# 2w3d: %SYS-5-CONFIG_I: Configured from console by console R5# R5# ! Notice that all routes are learned through the BRI0/0: ! Now we see the routes coming through interface BRI 0/0 R5#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area        * - candidate default, U - per-user static route, o - ODR        P - periodic downloaded static route Gateway of last resort is not set      50.0.0.0/24 is subnetted, 1 subnets O E2    50.5.5.0 [110/100] via 160.10.15.3, 00:00:08, BRI0/0      140.200.0.0/24 is subnetted, 1 subnets O E2    140.200.10.0 [110/1] via 160.10.15.3, 00:00:08, BRI0/0 O E2 193.118.9.0/24 [110/100] via 160.10.15.3, 00:00:08, BRI0/0 O E2 20.0.0.0/8 [110/1] via 160.10.15.3, 00:00:08, BRI0/0 O E2 193.118.8.0/24 [110/100] via 160.10.15.3, 00:00:08, BRI0/0 O E2 193.118.10.0/24 [110/100] via 160.10.15.3, 00:00:08, BRI0/0 O E2 193.118.5.0/24 [110/100] via 160.10.15.3, 00:00:09, BRI0/0 O E2 193.118.4.0/24 [110/100] via 160.10.15.3, 00:00:09, BRI0/0      160.10.0.0/16 is variably subnetted, 16 subnets, 2 masks O IA    160.10.37.5/32 [110/1674] via 160.10.15.3, 00:00:09, BRI0/0 O IA    160.10.32.0/24 [110/1626] via 160.10.15.3, 00:00:09, BRI0/0 O IA    160.10.37.4/32 [110/1674] via 160.10.15.3, 00:00:10, BRI0/0 O IA    160.10.33.0/24 [110/1563] via 160.10.15.3, 00:00:10, BRI0/0 O IA    160.10.37.2/32 [110/1626] via 160.10.15.3, 00:00:10, BRI0/0 O IA    160.10.37.1/32 [110/1674] via 160.10.15.3, 00:00:10, BRI0/0 O IA    160.10.11.0/24 [110/1684] via 160.10.15.3, 00:00:10, BRI0/0 C       160.10.15.0/24 is directly connected, BRI0/0 O IA    160.10.2.0/24 [110/1627] via 160.10.15.3, 00:00:10, BRI0/0 O IA    160.10.3.0/24 [110/1563] via 160.10.15.3, 00:00:10, BRI0/0 O IA    160.10.1.0/24 [110/1675] via 160.10.15.3, 00:00:10, BRI0/0 O       160.10.6.0/24 [110/1564] via 160.10.15.3, 00:00:20, BRI0/0 O IA    160.10.4.0/24 [110/1675] via 160.10.15.3, 00:00:10, BRI0/0 C       160.10.5.0/24 is directly connected, Loopback0 O IA    160.10.25.0/24 [110/1684] via 160.10.15.3, 00:00:10, BRI0/0 O       160.10.22.0/24 [110/1563] via 160.10.15.3, 00:00:20, BRI0/0 O E2 193.118.7.0/24 [110/100] via 160.10.15.3, 00:00:10, BRI0/0      40.0.0.0/24 is subnetted, 1 subnets O E2    40.4.4.0 [110/100] via 160.10.15.3, 00:00:01, BRI0/0      130.200.0.0/24 is subnetted, 1 subnets O E2    130.200.10.0 [110/100] via 160.10.15.3, 00:00:01, BRI0/0 O E2 193.118.6.0/24 [110/100] via 160.10.15.3, 00:00:01, BRI0/0 O E2 193.118.1.0/24 [110/100] via 160.10.15.3, 00:00:01, BRI0/0 O E2 193.118.3.0/24 [110/100] via 160.10.15.3, 00:00:01, BRI0/0 O E2 193.118.2.0/24 [110/100] via 160.10.15.3, 00:00:01, BRI0/0 R5#