Ospf Area Attribute Configuration; Configuration Prerequisites; Configuring Ospf Area Attributes - 3Com 5500-EI PWR Install Manual

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 redistribute any external route. For this reason the concept of NSSA is introduced.
Type-7 LSAs can be advertised in an NSSA. Type-7 LSAs are generated by ASBRs in the NSSA, and
will be transformed into Type-5 LSAs (AS-external LSAs) when 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

Follow these steps to configure OSPF area attributes:
To do...
Enter system view
Enter OSPF view
Enter OSPF area view
Configure the current area to be
a stub area
Configure the current area to be
an NSSA area
Configure the cost of the default
route transmitted by OSPF to a
stub or NSSA area
Use the command...
system-view
ospf [ process-id [ router-id
router-id ] ]
area area-id
stub [ no-summary ]
nssa
[ default-route-advertise |
no-import-route |
no-summary |
translate-always ] *
default-cost cost
4-15
Remarks
—
—
—
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.