•
default-information-originate
- When the router is an NSSA Area Border
Router (ABR) or an NSSA Autonomous System Boundary Router (ASBR),
this parameter causes it to generate a Type-7 default LSA into the NSSA.
This default provides a route to other areas within the AS for an NSSA ABR,
or to areas outside the AS for an NSSA ASBR.
Command Mode
Router Configuration
Default Setting
No NSSA is configured.
Command Usage
• There are no external routes in an OSPF stub area, so r outes can not be
redistributed from another protocol into a stub area. On th e other ha nd, an
NSSA allows external routes from another protocol to be red istr ibu ted into its
own area, and then leaked to adjacent areas.
• This command can be used to simplify admi nistra tion when connect ing a
central site using OSPF to a remote site that is using a dif ferent ro uting
protocol. You can extend OSPF to cover the remote connection by definin g
the area between the central router and the remote router as an NSSA.
• All routers in a NSSA must be configured with the same area ID.
• An NSSA is similar to a stub, because when the router is an ABR, it can
send a default route for other areas in the AS into the NSSA using the
default-
information-originate
keyword. However, an NSSA is different from a stub,
because when the router is an ASBR, it can import a default external AS route
(for routing protocol domains adjacent to the NSSA bu t not wit hin the OSP F
AS) into the NSSA using the
default-information-originate
keyword.
• External routes advertised into an NSSA can include netw ork destin ations
outside the AS learned via OSPF, the default route, static routes, routes
imported from other routing protocols such as RIP, and netwo rks direct ly
connected to the router that are not running OSPF.
• NSSA external LSAs (Type 7) are converted by any ABR adjacent to the NSSA
into external LSAs (Type-5), and propagated into other areas within the AS.
• Also, note that unlike stub areas, all Type-3 summa ry LSAs are always
imported into NSSAs to ensure that internal routes are always c hosen over
Type-7 NSSA external routes.
• This router supports up to 16 total areas (either normal transit areas, stubs, or
NSSAs).
Example
This example creates a stub area 10.3.0.0, and assigns all interfaces with class B
addresses 10.3.x.x to the NSSA. It also instructs the router to gener ate extern al
LSAs into the NSSA when it is an NSSA ABR or NSSA ASBR.
Console(config-router)#area 10.3.0.0 nssa default-information-originate
Console(config-router)#network 10.3.0.0 255.255.0.0 area 10.2.0.0
Console(config-router)#
42-29
Open Shortest Path First (OSPF)
42