| In the graphic, the central site and
branch office are interconnected through a slow WAN link. The branch
office is not using OSPF, but the central site is. Rather than
define a RIP domain to connect the sites, you can define an NSSA..
In this scenario, Router A is defined
as an ASBR. It is configured to redistribute any routes within the
RIP/EIGRP domain to the NSSA. The following is a description of what
happens when the area between the connecting routers is defined as
an NSSA:
- Router A receives RIP or EIGRP
routes for networks 10.10.0.0/16, 10.11.0.0/16, and 20.0.0.0/8.
- Because Router A is also
connected to an NSSA, it redistributes the RIP or EIGRP routers as
Type 7 LSAs into the NSSA.
- Router B, an ABR between the
NSSA and the backbone Area 0, receives the Type 7 LSAs.
- After the SPF calculation on the
forwarding database, Router B translates the Type 7 LSAs into Type
5 LSAs and then floods them throughout Backbone Area 0.
It is at this point that router B
could have summarized routes 10.10.0.0/16 and 10.11.0.0/16 as
10.0.0.0/8, or could have filtered one or more of the routes.
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