Asante Technologies 35516 - Manual (Page 73)

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Authentication allows password-based protection against unauthorized access to an area. Stub areas are areas into
which information on external routes is not sent. Instead, there is a default external route (generated by the area
border router) into the stub area for destinations outside the autonomous system. To further reduce the number of
link state advertisements sent into a stub area, no-summary configuration on the ABR is allowed to prevent it from
sending summary link advertisement into the stub area.
In router configuration mode, specify any of the following area parameters as needed for the network.
Command Purpose
area {area-id | area-address}
authentication Enable authentication for an OSPF area.
area {area-id | area-address}
authentication message-digest Enable MD5 authentication for an OSPF area.
area {area-id | area-address}
stub [no-summary] Define an area as a stub area.
area {area-id | area-address}
default-cost cost Assign a specific cost to the default summary route used for
the stub area.
area {area-id | area-address}
export-list access-list Define an area to be advertised into the other areas.
area {area-id | area-address}
import-list access-list Define an area to be allowed in the specified area.
area {area-id | area-address}
shortcut {default | disable |enable} Set shortcutting behavior through an area.
5.7.8 Configure OSPF Not So Stubby Area (NSSA)
The NSSA is similar to OSPF stub area. NSSA does not flood Type 5 external link state advertisements (LSAs) from
the core into the area, but it has the ability of importing AS external routes in a limited fashion within the area.
The OSPF Specification (RFC 1583) prohibits the summarizing or filtering of Type 5 LSAs. It is an OSPF requirement
that Type 5 LSAs always be flooding throughout a routing domain. NSSA allows importing specific external routes as
Type 7 LSAs into the NSSA. In addition, when translating Type 7 LSAs into Type 5 LSAs by NSSA ABR,
summarization and filtering are supported during the translation.
Use NSSA to simplify administration if you are an Internet Service Provider (ISP) or a network administrator that must
connect a central site using OSPF to a remote site that is using a different routing protocol such as RIP.
Prior to NSSA, the connection between the corporate site border router and the remote router could not be run as
OSPF stub area because routes for the remote site cannot be redistributed into stub area. With NSSA, you can
extend OSPF to cover the remote connection by defining the area between the corporate router and the remote
router as an NSSA.
In router configuration mode, specify the following area parameters as needed to configure OSPF NSSA.
Command Purpose
area area-id nssa [no-summary|
translate-always | translate-candidate
| translate-never] Set an area to be an NSSA.