Ospf Area Attribute Configuration - 3Com 7757 Configuration Manual

OSPF Area Attribute
Configuration
Configuration
Prerequisites
Configuring OSPF Area
Attributes
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.
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.
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
■
Table 232 Configure OSPF area attributes
Operation
Enter system view
Enter OSPF view
Enter OSPF area view
Configure the current area to be a
stub area
Configure an area to be an NSSA
area
Configure the cost of the default
route transmitted by OSPF to a stub
or NSSA area

OSPF Area Attribute Configuration

Command
system-view
ospf [ process-id
[ router-id router-id ] ]
area area-id
stub [ no-summary ]
nssa
[ default-route-advertis
e | no-import-route |
no-summary ]*
default-cost cost
311
Description
-
-
-
Optional
By default, no area is
configured as a stub area.
Optional
By default, no area is
configured as an NSSA
area.
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.