2-21 area transit-area-id virtual-link router-id retransmit-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 ” The range of values is 1 “8192 seconds. The default value is 5 seconds.

Purpose: When a router advertises a link-state advertisement (LSA) over a virtual link, the LSA is added to a retransmission list for the virtual link. The LSA will be retransmitted until the LSA is acknowledged . The number of seconds between the advertisements is called the retransmit interval.

Initial Cisco IOS Software Release: 10.0

Configuration Example: Modifying the Retransmit Interval Over a Virtual Link

Configure the network in Figure 2-21 to observe the default timer values over the virtual link. You will then experiment with adjusting the values of the retransmit interval.

Figure 2-21. The Retransmit Interval Is the Time Between Resending Unacknowledged LSAs

graphics/02fig21.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 retransmit interval is 5 seconds. Modify the configuration on Router B to change the retransmit interval to 6 seconds while leaving the value for the retransmit interval on Router C set to the default of 5 seconds.

 Router B  router ospf 1    area 1 virtual-link 3.3.3.3 retransmit-interval 6    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 40, Wait 40,  Retransmit 6  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, 00:03:53, 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, 00:03:54, 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

Router B has learned the routes being advertised by Router A and the routes advertised by Router C. Unlike the Hello interval (see Section 2-19) and the dead interval (see Section 2-18), the virtual link does not need to have the same retransmit interval configured on both ends of the link.

Verification

Verify that the new retransmit interval has been configured on Router C.

 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 6  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

Verification

The retransmit interval can be verified by using the show ip ospf virtual-links command.

 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 00:00:04     Adjacency State FULL (Hello suppressed)

Troubleshooting

Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbors 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 desired retransmit interval has been configured by using the command show ip ospf virtual-links.

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