© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Configuring OSPF OSPF Route Summarization

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Benefits of Route Summarization Minimizes number of routing table entries Localizes impact of a topology change Reduces LSA type 3 and 5 flooding and saves CPU resources

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Using Route Summarization Interarea summary link carries mask. One or more entries can represent several subnets.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v area area-id range address mask [advertise | not- advertise] [cost cost] Router(config-router)# Consolidates interarea routes on an ABR Configuring Route Summarization summary-address ip-address mask [not-advertise] [tag tag] Router(config-router)# Consolidates external routes, usually on an ASBR

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Route Summarization Configuration Example at ABR

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Route Summarization Configuration Example at ASBR

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Default Routes in OSPF A default route is injected into OSPF as an external LSA type 5. Default route distribution is not on by default; use the default-information originate command under the OSPF routing process.

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Normally, this command advertises a default into the OSPF network only if the default route already exists in the routing table. The always keyword allows the default to be advertised even when the default route does not exist in the routing table. default-information originate [always] [metric metric- value] [metric-type type-value] [route-map map-name] Router(config-router)# Configuring OSPF Default Routes

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Default Route Configuration Example

© 2006 Cisco Systems, Inc. All rights reserved. BSCI v Summary Route summarization improves CPU utilization, reduces LSA flooding, and reduces routing table sizes. The area range command is used to summarize at the ABR. The summary-address command is used to summarize at the ASBR. Default routes can be used in OSPF to prevent the need for a specific route to all destination networks. The benefits include a much smaller routing table and LSDB, with complete reachability. OSPF uses the default-information originate command to inject a default route.

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