Advanced Juniper Networks Routing Release 5 1 Revision

Advanced Juniper Networks Routing Release 5. 1, Revision 0 Module 2: OSPF Stub Areas

Module Objectives l Review the basic components of the OSPF Protocol l Discuss the OSPF neighbor hello protocol and adjacency formation process l Examine the function of the Link-State Database (LSDB) and how it contributes routes to the routing table l Look at the different kinds of OSPF packet types l Configure OSPF on a Juniper Networks router Copyright © 2001, Juniper Networks, Inc.

LSA Flooding: Default Area 0 LSA 1 Area 0 LSA 2 Area 1 LSA 3 Area 1 LSA 1 Area 1 LSA 2 Area 0 LSA 3 LSA 4 Area 2 Area 3 LSA 4 Area 3 Area 0 LSA 3 LSA 5 Area 1 Backbone (0. 0) Area 2 LSA 3 External Routes Area 0 LSA 5 Area 3 LSA 4 Area 2 LSA 1 Area 3 LSA 2 Area 0 LSA 3 LSA 4 Area 1 Area 0 LSA 3 LSA 5 Area 2 LSA 3 Area 3 LSA 5 Area 2 LSA 2 Area 0 LSA 3 Area 1 LSA 3 Area 3 LSA 3 Area 0 LSA 4 Area 3 LSA 4 Area 0 LSA 5 Area 3 LSA 5 Area 2 External Routes Copyright © 2001, Juniper Networks, Inc. Area 3

OSPF Stub Areas l Reduces the size of the link-state database – ABR does not inject Type 4 LSA into area – ABR does not flood Type 5 LSA into area l Reachability for routes external to OSPF is achieved via a 0/0 default route injected by the ABR – Manual configuration step for administrator control l ASBR in a stub area can’t flood LSAs for those routes l Virtual links can’t transit a stub area Copyright © 2001, Juniper Networks, Inc.

LSA Flooding: Stub Area 0 LSA 1 Area 0 LSA 2 Area 1 LSA 3 Area 1 LSA 1 Area 1 LSA 2 Area 0 LSA 3 Area 2 LSA 3 Area 3 LSA 3 Backbone (0. 0) Area 2 LSA 3 Area 0 LSA 5 Area 3 LSA 4 Area 2 LSA 1 Area 3 LSA 2 Area 0 LSA 3 LSA 4 Area 1 Area 0 LSA 3 LSA 5 Area 2 LSA 3 Area 3 LSA 5 Area 2 LSA 2 Area 0 LSA 3 Area 1 LSA 3 Area 3 LSA 3 Area 1 Stub External Routes Area 0 LSA 4 Area 3 LSA 4 Area 0 LSA 5 Area 3 LSA 5 Area 2 External Routes Copyright © 2001, Juniper Networks, Inc. Area 3

OSPF Stub No-Summaries Areas l Further reduces the size of the link-state database – ABR does not inject Type 3 LSA into area – ABR does not inject Type 4 LSA into area – ABR does not flood Type 5 LSA into area l Reachability for external routes is still via a 0/0 default route injected by the ABR – Again, a manual configuration step for administrator control l ASBR in a no-summaries area can’t flood LSAs for those routes l Virtual links can’t transit a no-summaries area Copyright © 2001, Juniper Networks, Inc.

LSA Flooding: Stub No-Summaries Area 0 LSA 1 Area 0 LSA 2 Area 1 LSA 3 Area 1 LSA 1 Area 1 LSA 2 Area 0 LSA 3 Area 2 LSA 3 Area 3 LSA 3 Backbone (0. 0) Area 2 LSA 3 Area 0 LSA 5 Area 3 LSA 4 Area 2 LSA 1 Area 3 LSA 1 Area 2 LSA 2 Area 0 LSA 3 Area 1 LSA 3 Area 3 LSA 3 Area 1 Stub External Routes Area 0 LSA 4 Area 3 LSA 4 Area 0 LSA 5 Area 2 External Routes Copyright © 2001, Juniper Networks, Inc. Area 3 LSA 2 Area 3 Stub No-Summaries

Stub Area Configuration l Each router in the area is required to configure itself as a stub router l The ABR can optionally inject a default route via the default-metric command [edit protocols ospf] user@area-1 -router# set area 1 stub user@area-1 -router# show area 0. 0. 0. 1 { stub; interface so-0/0/0. 0; } [edit protocols ospf] user@area-1 -abr# set area 1 stub default-metric 10 user@area-1 -abr# show area 0. 0. 0. 1 { stub default-metric 10; interface so-0/1/1. 0; } Copyright © 2001, Juniper Networks, Inc.

No-Summaries Area Configuration l Only the ABR is required to configure itself to support a no-summaries area l The ABR can optionally inject a default route via the default-metric command [edit protocols ospf] user@area-1 -abr# set area 1 stub no-summaries user@area-1 -abr# show area 0. 0. 0. 1 { stub default-metric 10 no-summaries; interface so-0/1/1. 0; } Copyright © 2001, Juniper Networks, Inc.

Area-Range l All local area routes are forwarded to the backbone by default – Stub only changes what enters an area, not what leaves l To summarize routing information headed to the backbone, use the area-range command l Only a single Type 3 LSA will be injected into the backbone l Configured on the ABR only [edit protocols ospf] user@host# set area 1 area-range 192. 168. 16/20 [edit protocols ospf] user@host# show area 0. 0. 0. 1 { area-range 192. 168. 16. 0/20; interface at-1/0/1. 100; } Copyright © 2001, Juniper Networks, Inc.

Area-Range Restrict l Adding the restrict keyword to the area-range command stops all routes in the range from entering the backbone l No Type 3 LSA will be injected into the backbone l Configured on the ABR only [edit protocols ospf] user@host# set area 1 area-range 192. 168. 16/20 restrict [edit protocols ospf] user@host# show area 0. 0. 0. 1 { area-range 192. 168. 16. 0/20 restrict; interface at-1/0/1. 100; } Copyright © 2001, Juniper Networks, Inc.

Review Questions Copyright © 2001, Juniper Networks, Inc.