Cisco OSPF Command and Configuration Handbook (paperback)
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2-12 area area-id stub no-summary
Syntax Description:
Purpose: Use of the no-summary keyword on the stub area's ABR creates a totally stubby area. In a totally stubby area, both external and inter-area OSPF routes are blocked from being advertised into the area. The backbone or Area 0 cannot be configured as a totally stubby area. An ASBR cannot be part of a totally stubby area, since the purpose of an ASBR is to inject external routes into OSPF. A totally stubby area cannot be used as the transit area for a virtual link. Initial Cisco IOS Software Release: 10.0 Configuration Example: Configuring an OSPF Totally Stubby Area
In Figure 2-14, Router C is redistributing connected interfaces into OSPF. These redistributed routes are OSPF external routes. Figure 2-14. An OSPF 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 clockrate 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 10.1.1.4 0.0.0.3 area 0 network 10.1.1.0 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 redistribute connected subnets network 10.1.1.4 0.0.0.15 area 0 Before configuring Area 1 as a totally stubby area, verify that the redistributed routes and OSPF inter-area 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, 00:00:02, 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, 00:00:02, Serial0/1 There is one OSPF external route and one OSPF inter-area route in the routing table on Router A. Configure Area 1 as a stub area by modifying the configurations on Routers A and B as shown in the following listing. 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 10.1.1.4 0.0.0.3 area 0 network 10.1.1.0 0.0.0.3 area 1 Verification
Verify that the external OSPF routes have been blocked from being advertised into the stub area. Also verify that the ABR is injecting a default route into the stub area. 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, 2 subnets C 10.1.1.0 is directly connected, Serial1 O IA 10.1.1.4 [110/128] via 10.1.1.2, 00:00:09, Serial0/1 O*IA 0.0.0.0/0 [110/65] via 10.1.1.2, 00:00:09, Serial0/1 Modify the configuration on Router B, the ABR, to create a totally stubby area. Router B router ospf 1 area 1 stub no-summary network 10.1.1.4 0.0.0.3 area 0 network 10.1.1.0 0.0.0.3 area 1 Verify that the OSPF inter-area routes are no longer being advertised by the ABR into the stub area. 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, 2 subnets C 10.1.1.0 is directly connected, Serial0/1 O*IA 0.0.0.0/0 [110/65] via 10.1.1.2, 00:00:17, Serial0/1 You can also verify that Router B is blocking OSPF inter-area routes or summary LSAs by using the command show ip ospf. 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 0x14946 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 17 times Area ranges are Number of LSA 4. Checksum Sum 0x204BF 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, no summary LSA in this area generates stub default route with cost 1 Area has no authentication SPF algorithm executed 25 times Area ranges are Number of LSA 7. Checksum Sum 0x424A1 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 Troubleshooting
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