Configuring OSPF Areas
Fixed Switch Configuration Guide 22-11
Router 3(su)->router(Config-router)#area 0.0.0.1 stub no-summary
Router 3(su)->router(Config-router)#area 0.0.0.1 default-cost 15
Router 5
Router 5(su)->router(Config)#router ospf 1
Router 5(su)->router(Config-router)#area 0.0.0.2 stub
Router 5(su)->router(Config-router)#area 0.0.0.2 default-cost 15
Router 6
Router 6(su)->router(Config)#router ospf 1
Router 6(su)->router(Config-router)#area 0.0.0.2 stub
Router 6(su)->router(Config-router)#area 0.0.0.2 default-cost 20
Router 7
Router 7(su)->router(Config)#router ospf 1
Router 7(su)->router(Config-router)#area 0.0.0.2 stub
Router 8
Router 8(su)->router(Config)#router ospf 1
Router 8(su)->router(Config-router)#area 0.0.0.2 stub
Configuring a Not So Stubby Area (NSSA)
A Not So Stubby Area (NSSA) is a hybrid area using an Autonomous System Border Router
(ASBR) to connect two disparate organizations. External routes are advertised as Type 7 LSAs and
are converted to Type 5 LSAs before flooding to the backbone by the NSSA’s ABR. Also, summary
routes are allowed into the NSSA while external routes from other networks are still filtered from
insertion into the NSSA.
External routes that are not imported into an NSSA can be represented by a default route. If the
router is an ABR and has the highest router ID of all ABRs in the area, it will translate Type 7 LSAs
into Type 5 LSAs.
When a translating ABR loses a translator election, it will stop translating, and after a number of
seconds, it will flush any Type 5 LSAs resulting from aggregation. Any Type 5 LSAs resulting
from direct translation of Type 7 LSAs will be allowed to age out. An ABR will always originate a
default route into any attached NSSAs.
Use the area nssa command to configure an area as a Not-So-Stubby-Area.
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