AIS Router AI2524 Manual do Utilizador descarregar pdf (Página 143)

Chapter 8: AI2524 Protocol Configuration Steps

August 1997 Page 8-5

2524UM

Define an area to be a stub area.

area

area-id

stub [no-summary]

Assign a specific cost to the default summary route used for th

stub area.

area

area-id

default-cost

cost

Configure OSPF Not So Stubby Area (NSSA)

NSSA area 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 can import AS external routes in a limited fashion within the

area.

NSSA allows importing of Type 7 AS external routes within NSSA

area by redistribution. These Type 7 LSAs are translated into Type 5

LSAs by NSSA Area Border Router (ABR), which are flooded

throughout the whole routing domain. 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 proto-

col.

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 could not be redistributed into stub area. A

simple protocol like RIP was usually run to handle the redistribution.

This meant maintaining two routing protocols. With NSSA, you can

extend OSPF to cover the remote connection by defining the area be-

tween the corporate router and the remote router as an NSSA.

In router configuration mode, specify these area parameters as needed

to configure OSPF NSSA:

area

area-id

nssa [no-redistribution]

[default-information-originate]

In router configuration mode on the ABR, specify this command to

control summarization and filtering of Type 7 LSA into Type 5 LSA

(optional):

summary address prefix mask [not advertise]

[tag tag]

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