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To configure an OSPF area as a NSSA,
you must configure all OSPF router interfaces that belong to the
area using the following command syntax:
Router(config-router)#area area-id nssa
[no-summary]
Typically, you should use the
optional keyword no-summary
when configuring NSSA on an ABR. This prevents Type 3 and Type 4
summary routes from flooding the NSSA area and minimizes the routing
tables within the area. In effect, the no-summary
keyword makes the NSSA totally stubby.
Optionally, you can control the
summarization or filtering during the translation using the
following syntax:
Router(config)#summary-address
prefix mask [not-advertise] [tag tag]
The not-advertise
keyword is used to suppress routes that match the prefix/mask pair.
This keyword applies to OSPF only. The tag
value can also be assigned but is not required. Route tags can be
used in policy routing and are discussed in Chapter 6, EIGRP.
To verify that NSSA is defined on a
given router, you can use the show
ip ospf command .
This command shows you general OSPF-configured parameters, including
the number of NSSAs to which the router is attached and whether the
router is performing LSA translation.
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