AIS Router AI2524 - Manual (Page 143)

Chapter 8: AI2524 Protocol Configuration Steps
August 1997 Page 8-5
2524UM
z Define an area to be a stub area.
area area-id stub [no-summary]
z 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]