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Default routing in NSSA area

The RFC 3101 (OSPF NSSA Option) states:
In addition, an NSSA border router should originate a default LSA (IP network is 0.0.0.0/0) into the NSSA. Default routes are necessary because NSSAs do not receive full routing information and must have a default route in order to route to AS-external destinations.
I am pretty sure that IOS inserted the type-7 default route into an NSSA area when the NSSA feature was introduced. Today (at least in IOS release 12.4, 12.4T and 12.2S) you have to configure the type-7 default route origination explicitly with the area nssa default-information-originate router configuration command, in which you can also specify the route metric and metric type (N1 or N2). Entering the area xx nssa without the default-information-originate keyword will result in an NSSA area with no connectivity to external destinations redistributed into OSPF in other areas.

You can find more information on OSPF default route behavior in the IP Corner article The OSPF Default Mysteries.

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