Filter
Top Products
DES-7200 Configuration Guide Chapter 4 OSPF
Configuration
4-13
the routing area of the OSPF.
Through redistribution, the external type-7 routes of the autonomous system are
allowed to import to the NSSA. These external type-7 LSAs will be converted into
the type-5 LSAs at the border router of the NSSA and flooded to the entire
autonomous system. During this process, the external routes can be summarized
and filtered.
You should pay attention to the following aspects when you configure the NSSA:
The backbone area cannot be configured as a NSSA, and the NSSA cannot
be used as the transmission area of the virtual links.
To set an area as the NSSA, all the routers connected to the NSSA must be
configured with the NSSA features by using the area nssa command.
To configure an area as the NSSA, execute the following commands in the routing
process configuration mode:
Command Function
DES-7200 (config-router)# area area-id
nssa
[no-redistribution] [no-summary]
[default-information-originate[metric
metric][metric-type [1 | 2]]]
(Optional) Define a NSSA.
DES-7200 (config-router)#area area-id
default-cost cost
Configure the cost of the default route
sent to the NSSA.
The default-information-originate parameter is used to generate the default
Type-7 LSA. This option varies slightly between the ARR and ASBR of the NSSA.
On the ABR, whether there is a default route or not in the routing table, the Type-7
LSA default route will be created. On the other hand, this is only created when
there is a default route in the routing table on ASBR.
The no-redistribution parameter allows other external routes introduced by
using the redistribute commands via the OSPF on the ASBR not to be
distributed to the NSSA. This option is usually used when the router in the NSSA
is both an ASBR and an ABR to prevent external routes from entering the NSSA.
To further reduce the LSAs sent to the NSSA, you can configure the no-summary
attribute on the ABR to prevent the ABR from sending the summary LSAs
(Type-3 LSA) to the NSSA.
In addition, the area default-cost is used on the ABR connected to the NSSA. This
command configures the cost of the default route sent by the border router to the
NSSA. By default, the cost of the default route sent to the NSSA is 1.