OSPF Area Attribute Configuration
311
■
The ID of an OSPF process is unique.
■
One segment can belong to only one area and you must specify each OSPF
interface to belong to a particular area.
OSPF Area Attribute
Configuration
Area partition in OSPF reduces the number of LSAs in the network and enhances
OSPF scalability. To further reduce routing table size and the number of LSAs in
some non-backbone areas on the edge of the AS, you can configure these areas as
stub areas.
A stub area cannot import any external route. For this reason the concept of NSSA
area is introduced. Type7 LSAs can be advertised in an NSSA area. Type7 LSAs are
generated by ASBRs of the NSSA area, and will be transformed into AS-external
LSAs whey reaching ABRs in the NSSA area, which will then be advertised to other
areas.
After area partition, the OSPF route updates between non-backbone areas are
exchanged by way of the backbone area. Therefore, OSPF requires that all the
non-backbone areas should keep connectivity with the backbone area and the
backbone area must keep connectivity in itself.
If the physical connectivity cannot be ensured due to various restrictions, you can
configure OSPF virtual links to satisfy this requirement.
Configuration
Prerequisites
Before configuring OSPF area attributes, perform the following tasks:
■
Configuring the network layer addresses of interfaces so that the adjacent
nodes are reachable to each other at the network layer
■
Performing basic OSPF configuration
Configuring OSPF Area
Attributes
Table 232
Configure OSPF area attributes
Operation Command
Description
Enter system view
system-view
-
Enter OSPF view
ospf
[
process-id
[
router-id
router-id
] ]
-
Enter OSPF area view
area
area-id
-
Configure the current area to be a
stub area
stub
[
no-summary
] Optional
By default, no area is
configured as a stub area.
Configure an area to be an NSSA
area
nssa
[
default-route-advertis
e
|
no-import-route
|
no-summary
]*
Optional
By default, no area is
configured as an NSSA
area.
Configure the cost of the default
route transmitted by OSPF to a stub
or NSSA area
default-cost
cost
Optional
This can be configured on
an ABR only. By default,
the cost of the default
route to a stub or NSSA
area is 1.
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