© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Configuring OSPF Configuring OSPF Special Area Types

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Types of Areas

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Stub and Totally Stub Area Rules An area can be stub or totally stub if: There is a single ABR, or if there is more than one ABR, suboptimal routing paths to other areas or external autonomous systems are acceptable. All routers in the area are configured as stub routers. There is no ASBR in the area. The area is not area 0. No virtual links go through the area.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v External LSAs are stopped. Default route is advertised into stub area by the ABR. All routers in area 50 must be configured as stub. Using Stub Areas

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Stub Area Configuration area area-id stub [no-summary] This command turns on stub area networking. All routers in a stub area must use the stub command. RouterA(config-router)# area area-id default-cost cost This command defines the cost of a default route sent into the stub area. The default cost is 1. RouterA(config-router)#

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v OSPF Stub Area Configuration Example

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v External LSAs are stopped. Summary LSAs are stopped. Routing table is reduced to a minimum. All routers must be configured as stub. ABR must be configured as totally stubby. This is a Cisco proprietary feature. Using Totally Stubby Areas

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v area area-id stub no-summary The addition of no-summary on the ABR creates a totally stubby area and prevents all summary LSAs from entering the stub area. Totally Stubby Configuration RouterA(config-router)#

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Totally Stubby Configuration Example

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Routing Table in a Standard Area P1R3#sh ip route Gateway of last resort is not set /32 is subnetted, 4 subnets O IA [110/782] via , 00:02:44, FastEthernet0/0 O IA [110/1] via , 00:02:44, FastEthernet0/0 O IA [110/782] via , 00:02:52, Serial0/0/0 [110/782] via , 00:02:52, FastEthernet0/0 O IA [110/782] via , 00:02:44, FastEthernet0/ /8 is variably subnetted, 7 subnets, 2 masks O /24 [110/782] via , 00:03:22, FastEthernet0/0 C /32 is directly connected, Loopback0 C /24 is directly connected, Serial0/0/0 O /24 [110/782] via , 00:03:23, Serial0/0/0 C /24 is directly connected, FastEthernet0/0 O /24 [110/782] via , 00:03:23, FastEthernet0/0 O E /24 [110/50] via , 00:02:39, FastEthernet0/0 P1R3#

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Routing Table in a Stub Area P1R3#sh ip route Gateway of last resort is to network /32 is subnetted, 4 subnets O IA [110/782] via , 00:01:49, FastEthernet0/0 O IA [110/1] via , 00:01:49, FastEthernet0/0 O IA [110/782] via , 00:01:49, Serial0/0/0 [110/782] via , 00:01:49, FastEthernet0/0 O IA [110/782] via , 00:01:49, FastEthernet0/ /8 is variably subnetted, 6 subnets, 2 masks O /24 [110/782] via , 00:01:50, FastEthernet0/0 C /32 is directly connected, Loopback0 C /24 is directly connected, Serial0/0/0 O /24 [110/782] via , 00:01:50, Serial0/0/0 C /24 is directly connected, FastEthernet0/0 O /24 [110/782] via , 00:01:50, FastEthernet0/0 O*IA /0 [110/2] via , 00:01:51, FastEthernet0/0 P1R3#

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Routing Table in a Stub Area with Summarization P1R3#sh ip route Gateway of last resort is to network /16 is variably subnetted, 2 subnets, 2 masks O IA /32 [110/782] via , 00:13:08, FastEthernet0/0 O IA /24 [110/1] via , 00:02:39, FastEthernet0/ /8 is variably subnetted, 6 subnets, 2 masks O /24 [110/782] via , 00:13:08, FastEthernet0/0 C /32 is directly connected, Loopback0 C /24 is directly connected, Serial0/0/0 O /24 [110/782] via , 00:13:09, Serial0/0/0 C /24 is directly connected, FastEthernet0/0 O /24 [110/782] via , 00:13:09, FastEthernet0/0 O*IA /0 [110/2] via , 00:13:09, FastEthernet0/0 P1R3#

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Routing Table in a Totally Stubby Area P1R3#sh ip route Gateway of last resort is to network /8 is variably subnetted, 6 subnets, 2 masks O /24 [110/782] via , 00:16:53, FastEthernet0/0 C /32 is directly connected, Loopback0 C /24 is directly connected, Serial0/0/0 O /24 [110/782] via , 00:16:53, Serial0/0/0 C /24 is directly connected, FastEthernet0/0 O /24 [110/782] via , 00:16:53, FastEthernet0/0 O*IA /0 [110/2] via , 00:00:48, FastEthernet0/0 P1R3#

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v NSSA breaks stub area rules. ASBR (R1) is allowed in NSSA. Special LSA type 7 defined, sent by ASBR. ABR (R2) converts LSA type 7 to LSA type 5. ABR sends default route into NSSA instead of external routes from other ASBRs. NSSA is an RFC addendum. Not-So-Stubby Areas

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v area area-id nssa [no-redistribution] [default- information-originate [metric metric-value] [metric- type type-value]] [no-summary] Use this command instead of the area stub command to define the area as NSSA. The no-summary keyword creates an NSSA totally stubby area; this is a Cisco proprietary feature. NSSA Configuration RouterA(config-router)#

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Example: NSSA Configuration

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v NSSA Totally Stubby Configuration NSSA totally stubby area is a Cisco proprietary feature.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v show ip ospf Displays which areas are normal, stub, or NSSA show Commands for Stub and NSSA show ip ospf database Displays details of LSAs show ip ospf database nssa-external Displays specific details of each LSA type 7 update in database show ip route Displays all routes RouterA#

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Summary There are several OSPF area types: standard, backbone, stub, totally stubby, and NSSA. Use the area area-id stub command to define an area as stubby. Use the area area-id stub command with the no-summary keyword on the ABR only to define an area as totally stubby. For stub areas, external routes are not visible in the routing table, but are accessible via the intra-area default route. For totally stubby areas, interarea and external routes are not visible in the routing table, but are accessible via the intra-area default route. Use the area area-id nssa command to define an area as NSSA. Use show ip ospf, show ip ospf database, show ip route commands to verify all types of stub areas. Use the show ip ospf database nssa-external command to display details of type 7 LSAs.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v