Content

| 6.7 |  | Stub, Totally Stubby, and Not-So-Stubby Areas |
| 6.7.8 |  | Configuring NSSA |

To configure an OSPF area as a NSSA, 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, 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, the summarization or filtering can be controlled 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 and 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 Module 5, EIGRP.

To verify that NSSA is defined on a given router, use the show ip ospf command. This command shows the general OSPF configured parameters, including the number of NSSAs to which the router is attached and whether the router is performing LSA translation.

| Lab Activity e-Lab Activity: Configuring NSSA In this lab, configure an OSPF area as a NSSA.