H3C S7500E Series Ethernet Switches Operation Manual

Operation Manual – IPv4 Routing
H3C S7500E Series Ethernet Switches Chapter 3 OSPF Configuration
3-24
3.4 Configuring OSPF Area Parameters
Splitting an OSPF AS into multiple areas reduces the number of LSAs in the networks
and extends the OSPF application. For those non-backbone areas residing on the AS
boundary, you can configure them as stub areas to further reduce the size of routing
tables on routers in these areas and the number of LSAs.
A stub area cannot redistribute routes, and for this reason, NSSA was introduced. In
NSSA areas, Type-7 LSAs (NSSA External LSAs) can be advertised. Type 7 LSAs
originate from the ASBR in a NSSA area. When arriving at the ABR in the NSSA area,
these LSAs will be translated into type 5 LSAs for advertisement to other areas.
Non-backbone areas exchange routing information via the backbone area. Therefore,
the backbone and non-backbone areas, including the backbone itself must maintain
connectivity.
If necessary physical links are not available for this connectivity maintenance, you can
configure virtual links to solve it.
3.4.1 Prerequisites
Before configuring an OSPF area, you have configured:
z IP addresses for interfaces, making neighboring nodes accessible with each other
at the network layer.
z OSPF basic functions.
3.4.2 Configuration Procedure
Follow these steps to configure OSPF area parameters:
To do… Use the command… Remarks
Enter system view
system-view
—
Enter OSPF view
ospf [ process-id |
router-id router-id ] *
—
Enter area view
area area-id
—
Configure the area as a
stub area
stub [ no-summary ]
Optional
Not configured by default
Configure the area as an
NSSA area
nssa
[ default-route-advertise
| no-import-route |
no-summary ] *
Optional
Not configured by default
Specify a cost for the
default route advertised to
the stub or NSSA area
default-cost cost
Optional
Defaults to 1.