Configuring the ECN330-switch
4431553-KDU 137 365 Uen D 2006-06-16
Figure 197 OSPF Stub Area
By default, a stub can only pass traffic to other areas in the autonomous system
through the default external route. However, an area border router can also be
configured to
send Type 3 summary link advertisements into the stub.
NSSA – A not-so-stubby area (NSSA) is similar to a stub. It blocks most external
routing information, and can be configured to advertise a single default route for
traffic passing between the NSSA and other areas within the autonomous
system (AS). However, an NSSA can also import external routes from one or
more small routing domains that are not part of the AS, such as a RIP domain
or locally configured static routes. This external AS routing information is
generated by the NSSA’s ASBR and advertised only within the NSSA. By
default, these routes are not flooded onto the backbone or into any other area
by area border routers. However, the NSSA’s ABRs will convert NSSA external
LSAs (Type 7) into external LSAs (Type-5) which are propagated into other
areas within the AS.
Figure 198 OSPF NSSA
backbone
stub
ABR
default
external
route
backbone
NSSA
ABR
default external
route for local AS
ASBR
external network
Router
default external
route for another
routing domain
7
5
AS
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