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Configuring OSPF 433
In the following group network, an AS operating the OSPF protocol includes three
areas, area 1, area 2, and area 0. Area 0 is the backbone area. The other ASs
operate RIP. Area 1 is defined as an NSSA area. After an RIP route advertises to the
NSSA ASBR that generates a Type-7 LSA and propagates in Area 1. After the
Type-7 LSA reaches the NSSA ABR, it is transformed into a Type-5 LSA that is
advertised to Area 0 and Area 2. The RIP route is generated as a Type-5 LSA and
propagated in the OSPF AS by the ASBR of Area 2. This Type-5 LSA will not reach
Area 1 because Area 1 is an NSSA area. On this point, an NSSA area and a stub
area are the same.
Figure 146 Schematic Diagram of an NSSA Area
Perform the following configuration in OSPF view:
Table 499 Configure an NSSA Area of OSPF
By default, no area is configured as an NSSA area.
The default-route-advertise attribute generates default a Type-7 LSA. A
Type-7 LSA default route is generated on the ABR no matter whether there is a
default route 0.0.0.0 in the routing table while applying this parameter. A Type-7
LSA default route is only generated on an ASBR when there is a default route
0.0.0.0 in the routing table.
The no-import-route attribute is used on the ASBR, which allows the OSPF route
that is imported using the
import-route command, to not be advertised to the
NSSA area. If the NSSA router is both ASBR and ABR, this parameter option is
always selected.
Configuring Route
Summarization within
the OSPF Domain
.
Route summary provides that the routing information is processed in the ABR.
Only one route is sent to other areas for the network segment configured with
summary. One area can be configured with multiple summary network segments
so that OSPF can summarize multiple network segments. When the ABR sends
routing information to other areas, Sum_net_Lsa (Type 3 LSA) is generated for
each network segment. If there are some continuous network segments in the
area, they can be summarized into one network segment with a range command.
Then the ABR only sends one summery LSA and all other LSAs in the summary
network segment range specified with this command are not sent separately,
Operation Command
Configure an area as NSSA area nssa area area-id [
default-route-advertise ] [
no-import-route ] [ no-summary ]
Cancel the configured NSSA area undo nssa area area-id
area 0
area 1
NSSA
Router
area 2
Router
Router
RIP
Router
Router
RIP
NSSA
ASBR
NSSA
ABR