Switch 7700 Configuration Guide

OSPF 87
All routers connected to the NSSA must use the nssa command to configure the
area with the NSSA attribute.
The default-route-advertise parameter is used to generate the default type-7
LSAs. The default type-7 LSA route is generated on the ABR, even though the
default route 0.0.0.0 is not in the routing table. On an ASBR, however, the default
type-7 LSA route can be generated only if the default route 0.0.0.0 is in the
routing table.
Executing the no-import-route command on the ASBR prevents the external
routes that OSPF imported through the import-route command from advertising
to the NSSA. Generally, if an NSSA router is both ASBR and ABR, this argument is
used.
The default-cost command is used on the ABR attached to the NSSA. Using this
command, you can configure the default route cost on the ABR to NSSA.
By default, the NSSA is not configured, and the cost of the default route to the
NSSA is 1.
Configure the Route Summarization of OSPF Area
Route summary means that ABR can aggregate information of the routes of the
same prefix and advertise only one route to other areas. An area can be
configured with multiple aggregate segments allowing OSPF to summarize them.
When the ABR transmits routing information to other areas, it generates
Sum_net_Lsa (type-3 LSA) per network. If some continuous networks exist in this
area, you can use the abr-summary command to summarize these segments into
one segment. Thus, the ABR only needs to send an aggregate LSA, and all the
LSAs in the range of the aggregate segment specified by the command are not
transmitted separately. Therefore, the sizes of the LSDBs in other areas can be
reduced.
Once the aggregate segment of a certain network is added to the area, all the
internal routes of the IP addresses in the range of the aggregate segment are no
longer separately broadcast to other areas. Only the route summary of the whole
aggregate network is advertised. But if the range of the segment is restricted by
the not-advertise keyword, the route summary of this segment is not advertised.
This segment is represented by an IP address and mask. The receiving and
restriction of the aggregate segment can reduce the routing traffic exchanged
between the areas.
Route summarization can take effect only when it is configured on ABRs.
Restore the default cost value
of the route to the NSSA area
undo default-cost
Table 35 Configure NSSA of OSPF
Operation Command