Configuring Nssa Of Ospf - Huawei Quidway S3500 Series Operation Manual

Operation Manual - Routing Protocol
Quidway S3500 Series Ethernet Switches
Please pay attention to the following items when configuring a STUB area:
The backbone area cannot be configured to be the STUB area and the virtual link
cannot pass through the STUB area.
If you want to configure an area to be the STUB area, then all the routers in this
area should be configured with this attribute.
No ASBR can exist in a STUB area. In other words, the external routes of the AS
cannot be propagated in the STUB area.
Perform the following configuration in OSPF Area view.
Table 4-14 Configuring STUB area of OSPF
Configure an area to be the STUB area
Remove the configured STUB area
Configure the cost of the default route
transmitted by OSPF to the STUB area
Remove the cost of the default route to
the STUB area
By default, the STUB area is not configured, and the cost of the default route to the
STUB area is 1.

4.2.15 Configuring NSSA of OSPF

NSSA areas are areas that can import external routing by itself and advertise in the
autonomous system, not accepting external routing generated by other area in the
autonomous system. Actually NSSA area is one deformation of Stub area, which can
conditionally import AS external routing. A new area-NSSA Area and a new LSA-NSSA
LSA (or called Type-7 LSA) are added in the RFC1587 OSPF NSSA Option.
NSSA and Stub area are similar in many ways. Neither of them generates or imports
AS-External-LSA (namely Type-5 LSA), and both of them can generate and import
Type-7 LSA. Type-7 LSA is generated by ASBR of NSSA area, which can only
advertise in NSSA area. When Type-7 LSA reaches ABR of NSSA, ABR will select
whether to transform Type-7 LSA into AS-External-LSA so as to advertise to other
areas.
For example, in the networking below, the AS running OSPF comprises three areas:
Area 1, Area 2 and Area 0. Among them, Area 0 is the backbone area. Also, there are
other two ASs respectively running RIP. Area 1 is defined as an NSSA. After RIP routes
of the Area 1 are propagated to the NSSA ASBR, the NSSA ASBR will generate type-7
LSAs which will be propagated in Area 1. When the type-7 LSAs reach the NSSA ABR,
the NSSA ABR will transform it into type-5 LSA, which will be propagated to Area 0 and
Area 2. On the other hand, RIP routes of the AS running RIP will be transformed into
Operation
Huawei Technologies Proprietary
4-13
Chapter 4 OSPF Configuration
Command
stub [ no-summary ]
undo stub
default-cost value
undo default-cost