You must explicitly configure an area to be a Not-So-Stubby Area (NSSA) area. NSSAs are similar to stub areas in that no external routes are imported into the area from other OSPF areas. The major difference between a stub area and an NSSA is an NSSA has the capability to flood external routes it learns throughout its area and by an area border router to the entire OSPF domain. An area cannot be both a stub area and an NSSA.
If this area is configured as a transit area for a virtual link, then existing virtual links of a non-stub or NSSA area are removed when its designation is changed to NSSA or stub.
Use the following syntax to configure stub areas.
ospf ospf-instance
area area-id
nssa
area-range ip-prefix/mask [advertise|not-advertise]
originate-default-route [type-7]
redistribute-external
summariesA:ALA-49>config>router>ospf# info
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asbr
overload
overload-on-boot timeout 60
traffic-engineering
export "OSPF-Export"
graceful-restart
helper-disable
exit
area 0.0.0.0
exit
area 0.0.0.20
stub
exit
exit
area 0.0.0.25
nssa
exit
exit
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A:ALA-49>config>router>ospf#