2-18 area transit-area-id virtual-link router-id dead-interval seconds

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Syntax Description:

transit-area-id ” The OSPF area ID of the area connecting the two ABRs that the virtual link will cross. This value can be entered as a decimal number in the range of 0 to 4,294,967,295 or in IP address form in the range 0.0.0.0 to 255.255.255.255. The transit area cannot be a stub area.
router-id ” OSPF router ID of the router at the remote end of the virtual link.
seconds ” If Hello packets from a neighbor are not received during a period of time equal to the dead interval, then the neighbor will be declared down. The range of values is 1 “8192 seconds. The default value is 40 seconds.

Purpose: When an OSPF router receives a Hello packet from an OSPF neighbor, the receiving router assumes that the neighbor is active. The dead interval is used to determine when an OSPF neighbor has become inactive. If a Hello packet has not been received during the time set for the dead interval, then the neighbor will be declared down. By default, the dead interval is four times the Hello interval. The dead interval should always be greater than the Hello interval.

Initial Cisco IOS Software Release: 10.0

Configuration Example: Modifying the Dead Interval Over a Virtual Link

Configure the network in Figure 2-18 to observe the default timer values over the virtual link. You will then experiment with adjusting the values of the dead interval.

Figure 2-18. The Dead Interval Must Be Configured with the Same Value at Both Ends of an OSPF Virtual Link

graphics/02fig18.gif

 Router A  interface Loopback0   ip address 1.1.1.1 255.255.255.255   !   interface Serial0/1   ip address 10.1.1.1 255.255.255.252   clockrate 64000   !   router ospf 1   network 10.1.1.0 0.0.0.3 area 0   network 1.1.1.1 0.0.0.0 area 0  _______________________________________________________________________ Router B  interface Loopback0   ip address 2.2.2.2 255.255.255.255   !   interface Serial0   ip address 10.1.1.2 255.255.255.252   !   interface Serial1   ip address 10.1.1.5 255.255.255.252   clockrate 64000   !   router ospf 1    area 1 virtual-link 3.3.3.3    network 10.1.1.0 0.0.0.3 area 0   network 2.2.2.2 0.0.0.0 area 0   network 10.1.1.4 0.0.0.3 area 1  _______________________________________________________________________ Router C  interface Loopback0   ip address 3.3.3.3 255.255.255.255   !   interface Serial0   ip address 10.1.1.6 255.255.255.252   !   router ospf 1    area 1 virtual-link 2.2.2.2    network 3.3.3.3 0.0.0.0 area 2   network 10.1.1.4 0.0.0.3 area 1

Verify that the virtual link is active and that all OSPF routes are being exchanged.

 rtrB#  show ip ospf virtual-links   Virtual Link OSPF_VL0 to router 3.3.3.3 is up  Run as demand circuit   DoNotAge LSA allowed.   Transit area 1, via interface Serial1, Cost of using 64   Transmit Delay is 1 sec, State POINT_TO_POINT,  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5   Hello due in 00:00:03  Adjacency State FULL (Hello suppressed) _______________________________________________________________________ rtrC#  show ip ospf virtual-links   Virtual Link OSPF_VL7 to router 2.2.2.2 is up  Run as demand circuit   DoNotAge LSA allowed.   Transit area 1, via interface Serial0, Cost of using 64   Transmit Delay is 1 sec, State POINT_TO_POINT,  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5   Hello due in 00:00:06  Adjacency State FULL (Hello suppressed) rtrC#  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, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets  O       1.1.1.1 [110/129] via 10.1.1.5, 00:02:25, Serial0  2.0.0.0/32 is subnetted, 1 subnets  O       2.2.2.2 [110/65] via 10.1.1.5, 00:02:26, Serial0  3.0.0.0/24 is subnetted, 1 subnets C       3.3.3.0 is directly connected, Loopback0      10.0.0.0/30 is subnetted, 2 subnets O       10.1.1.0 [110/128] via 10.1.1.5, 00:02:26, Serial0  C       10.1.1.4 is directly connected, Serial0

Notice that the default Hello interval is 10 seconds and the default dead interval is 40 seconds. Modify the configuration on Router B to change the dead interval to 41 seconds while leaving the value for the dead interval on Router C set to the default of 40 seconds.

 Router B  router ospf 1    area 1 virtual-link 3.3.3.3 dead-interval 41    network 2.2.2.2 0.0.0.0 area 0   network 10.1.1.0 0.0.0.3 area 0   network 10.1.1.4 0.0.0.3 area 1

Is the virtual link still active?

 rtrB#  show ip ospf virtual-links  Virtual Link OSPF_VL0 to router 3.3.3.3 is up   Run as demand circuit   DoNotAge LSA allowed.   Transit area 1, via interface Serial1, Cost of using 64   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured, Hello 10,  Dead 41  , Wait 40, Retransmit 5     Hello due in 00:00:07

The virtual link is up. Now check to see if the OSPF routes are being exchanged.

 rtrB#  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, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets O       1.1.1.1 [110/65] via 10.1.1.1, 00:07:49, Serial0      2.0.0.0/32 is subnetted, 1 subnets C       2.2.2.2 is directly connected, Loopback0      10.0.0.0/30 is subnetted, 2 subnets C       10.1.1.0 is directly connected, Serial0 C       10.1.1.4 is directly connected, Serial1

Router B has learned the routes being advertised by Router A but not the routes advertised by Router C. Because the dead interval time on Router B does not match the dead inter- val on Router C, routes will not be exchanged over the virtual link. Modify the dead interval time on Router C to match the dead interval time on Router B.

 Router C  router ospf 1   router ospf 1    area 1 virtual-link 2.2.2.2 dead-interval 41    network 3.3.3.3 0.0.0.0 area 2   network 10.1.1.4 0.0.0.3 area 1

Verification

Verify that the dead interval on Router C matches the dead interval on Router B.

 rtrC#  show ip ospf virtual-links  Virtual Link OSPF_VL7 to router 2.2.2.2 is up   Run as demand circuit   DoNotAge LSA allowed.   Transit area 1, via interface Serial0, Cost of using 64   Transmit Delay is 1 sec, State POINT_TO_POINT,   Timer intervals configured, Hello 10,  Dead 41  , Wait 40, Retransmit 5     Hello due in 00:00:00     Adjacency State FULL (Hello suppressed)

Verify that all OSPF routes are now being exchanged.

 rtrA#  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, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets  C       1.1.1.1 is directly connected, Loopback0  2.0.0.0/32 is subnetted, 1 subnets  O       2.2.2.2 [110/65] via 10.1.1.2, 00:09:04, Serial0/1  3.0.0.0/32 is subnetted, 1 subnets  O IA    3.3.3.3 [110/129] via 10.1.1.2, 00:09:04, Serial0/1  10.0.0.0/30 is subnetted, 2 subnets C       10.1.1.0 is directly connected, Serial0/1 O IA    10.1.1.4 [110/128] via 10.1.1.2, 00:09:04, Serial0/1 _______________________________________________________________________ rtrB#  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, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets  O       1.1.1.1 [110/65] via 10.1.1.1, 00:10:19, Serial0  2.0.0.0/32 is subnetted, 1 subnets  C       2.2.2.2 is directly connected, Loopback0  3.0.0.0/32 is subnetted, 1 subnets  O IA    3.3.3.3 [110/65] via 10.1.1.6, 00:10:20, Serial1  10.0.0.0/30 is subnetted, 2 subnets C       10.1.1.0 is directly connected, Serial0 C       10.1.1.4 is directly connected, Serial1 _______________________________________________________________________ rtrC#  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, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets  O       1.1.1.1 [110/129] via 10.1.1.5, 00:11:10, Serial0  2.0.0.0/32 is subnetted, 1 subnets  O       2.2.2.2 [110/65] via 10.1.1.5, 00:11:11, Serial0  3.0.0.0/24 is subnetted, 1 subnets  C       3.3.3.0 is directly connected, Loopback0  10.0.0.0/30 is subnetted, 2 subnets O       10.1.1.0 [110/128] via 10.1.1.5, 00:11:11, Serial0 C       10.1.1.4 is directly connected, Serial0

Troubleshooting

Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbor command.

Step 2. Verify that the transit area ID used in the area virtual-link command is the proper area.

Step 3. Verify that the router IDs used in the area virtual-link are correct.

Step 4. Verify that the dead interval is being used on both ends of the virtual link.

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