Switch 7700 Configuration Guide, v2

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OSPF 87

Figure 5 NSSA

Perform the following configuration in OSPF Area view.

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

Table 36 Configure NSSA of OSPF

Operation Command

Configure an area to be the

NSSA area

nssa [ default-route-advertise ] [ no-import-route ] [

no-summary ]

Cancel the configured NSSA undo nssa

Configure the default cost

value of the route to the NSSA

default-cost cost

Restore the default cost value

of the route to the NSSA area

undo default-cost

RIP

Area 2

Area 0

Area 1

NSSA

ABR

NSSA

ASBR