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2-3 area area-id default-cost costNOTE This command requires the following additional commands: area area-id nssa (see Section 2-4) or area area-id stub (see Section 2-11) Syntax Description:
Purpose: External networks will not be advertised into a stub or totally stubby area. External networks are networks that have been redistributed into OSPF. External OSPF routes and inter-area OSPF routes are not advertised into a totally stubby area. When an OSPF area is configured as a stub area, a default route will be generated by the ABR into the stub area in place of the external routes. When an OSPF area is configured as a totally stubby area, the default route replaces the external and inter-area routes. The purpose of this command is to set the cost of the default route advertised into a stubby, totally stubby, or not-so-stubby area. If this command is not used, then the cost of the default route will be 1. When configuring stub areas, all routers with interfaces in the stub area must be configured with the same stub area type. Initial Cisco IOS Software Release: 10.0 Configuration Example: Setting the Default Cost for a Stub AreaInitially, the network in Figure 2-3 is configured without a stubby area to compare the differences between the routes advertised into a normal area with those advertised into a stubby area. You will redistribute the loopback interface on Router C in order to generate an external route on Routers A and B. Figure 2-3. External OSPF Routes Are Not Advertised into an OSPF Stub Area. Inter-area and External Routes Are Not Advertised into a Totally Stubby Area
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 clock rate 64000 ! router ospf 1 network 10.1.1.0 0.0.0.3 area 1 _______________________________________________________________________ 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 clock rate 64000 ! router ospf 1 network 10.1.1.0 0.0.0.3 area 1 network 10.1.1.4 0.0.0.3 area 0 _______________________________________________________________________ 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 redistribute connected subnnets network 10.1.1.4 0.0.0.3 area 0 If you examine the IP routing table on Router A, you can see that all OSPF routes are being advertised into Area 1. 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 3.0.0.0/32 is subnetted, 1 subnets O E2 3.3.3.3 [110/20] via 10.1.1.2, 00:00:04, Serial0/1 10.0.0.0/30 is subnetted, 3 subnets C 10.1.1.0 is directly connected, Serial0/1 O IA 10.1.1.4 [110/128] via 10.1.1.2, 00:00:04, Serial0/1 Modify the configurations on Routers A and B so that Area 1 is a stub area. Router A router ospf 1 area 1 stub network 10.1.1.0 0.0.0.3 area 1 _______________________________________________________________________ Router B router ospf 1 area 1 stub network 10.1.1.0 0.0.0.3 area 1 network 10.1.1.4 0.0.0.3 area 0 Re-examine the IP routing table on Router A. 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 10.1.1.2 to network 0.0.0.0 1.0.0.0/32 is subnetted, 1 subnets C 1.1.1.1 is directly connected, Loopback0 10.0.0.0/30 is subnetted, 3 subnets C 10.1.1.0 is directly connected, Serial0/1 O IA 10.1.1.4 [110/128] via 10.1.1.2, 00:00:06, Serial0/1 O*IA 0.0.0.0/0 [110/65] via 10.1.1.2, 00:00:06, Serial0/1 Notice that the cost of the default route is 65. This is the sum of the cost to the ABR of 64 and the cost of the default route, which has the default value of 1. You can verify the default cost by using the command show ip ospf on Router B. rtrB# show ip ospf Routing Process "ospf 1" with ID 2.2.2.2 Supports only single TOS(TOS0) routes It is an area border router SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs Number of external LSA 3. Checksum Sum 0x14B45 Number of DCbitless external LSA 0 Number of DoNotAge external LSA 0 Number of areas in this router is 2. 1 normal 1 stub 0 nssa Area BACKBONE(0) Number of interfaces in this area is 1 Area has no authentication SPF algorithm executed 21 times Area ranges are Number of LSA 3. Checksum Sum 0x14F55 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 Area 1 Number of interfaces in this area is 1 It is a stub area generates stub default route with cost 1 Area has no authentication SPF algorithm executed 37 times Area ranges are Number of LSA 4. Checksum Sum 0x1E701 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 Modify the cost of the default route being generated by Router B. Router B router ospf 1 area 1 stub area 1 default-cost 15 Network 10.1.1.0 0.0.0.3 area 1 Network 10.1.1.4 0.0.0.3 area 0 VerificationVerify the new cost for the default route on Router A by using the show ip route command or the show ip route 0.0.0.0 command. You can also verify the cost of the default route on Router B by using the show ip ospf command. 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 10.1.1.2 to network 0.0.0.0 1.0.0.0/32 is subnetted, 1 subnets C 1.1.1.1 is directly connected, Loopback0 10.0.0.0/30 is subnetted, 3 subnets C 10.1.1.0 is directly connected, Serial0/1 O IA 10.1.1.4 [110/128] via 10.1.1.2, 00:03:39, Serial0/1 O*IA 0.0.0.0/0 [110/79] via 10.1.1.2, 00:00:09, Serial0/1 rtrA# show ip route 0.0.0.0 Routing entry for 0.0.0.0/0, supernet Known via "ospf 1", distance 110, metric 79, candidate default path, type inte r area Redistributing via ospf 1 Last update from 10.1.1.2 on Serial0/1, 00:01:05 ago Routing Descriptor Blocks: * 10.1.1.2, from 2.2.2.2, 00:01:05 ago, via Serial0/1 Route metric is 79, traffic share count is 1 _______________________________________________________________________ rtrB# show ip ospf Routing Process "ospf 1" with ID 2.2.2.2 Supports only single TOS(TOS0) routes It is an area border router SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs Number of external LSA 3. Checksum Sum 0x14B45 Number of DCbitless external LSA 0 Number of DoNotAge external LSA 0 Number of areas in this router is 2. 1 normal 1 stub 0 nssa Area BACKBONE(0) Number of interfaces in this area is 1 Area has no authentication SPF algorithm executed 21 times Area ranges are Number of LSA 3. Checksum Sum 0x14F55 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 Area 1 Number of interfaces in this area is 1 It is a stub area generates stub default route with cost 15 Area has no authentication SPF algorithm executed 37 times Area ranges are Number of LSA 4. Checksum Sum 0x27068 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 The new cost is now 64 + 15 or 79. Troubleshooting
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