3Com 7700 Configuration Manual page 94

86 C 5: R P
HAPTER OUTING
O
ROTOCOL PERATION
Table 34 Configure an OSPF STUB Area
Operation
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 a
STUB area is 1.
Configure NSSA of OSPF
NSSA and NSSA LSA (also called Type-7 LSA) are transformations of the STUB area
and are highly similar to a STUB area. NSSA does not allow importing
AS-External-LSAs (type-5 LSAs) but it does allow importing AS-External-LSA
(type-7 LSAs).
Type-7 LSAs are generated by the ASBRs in an NSSA, and propagated in the NSSA.
When the type-7 LSAs reach an ABR of the NSSA, the ABR translates the type-7
LSAs into AS-External-LSAs, which is propagated to the other areas.
For example, in Figure 5, the AS running OSPF includes three areas: Area 1, Area 2
and Area 0. Among them, Area 0 is the backbone area. Also, there are other two
ASs running RIP. Area 1 is defined as an NSSA. After RIP routes of Area 1 are
propagated to the NSSA ASBR, the NSSA ASBR generates type-7 LSAs which are
propagated in Area 1. When the type-7 LSAs reach the NSSA ABR, the NSSA ABR
translates it into a type-5 LSA, which is propagated to Area 0 and Area 2. On the
other hand, RIP routes of the AS running RIP are translated into type-5 LSAs that
are propagated in the OSPF AS. However, the type-5 LSAs do not reach Area 1
because Area 1 is an NSSA. NSSAs and STUB areas have the same approach in this
aspect.
Similar to a STUB area, the NSSA cannot be configured with virtual links.
Figure 5 NSSA
RIP
Area 2
Perform the following configuration in OSPF Area view.
Table 35 Configure NSSA of OSPF
Operation
Configure an area to be the
NSSA area
Cancel the configured NSSA
Configure the default cost
value of the route to the NSSA
Command
undo default-cost
NSSA
ABR
Area 1
NSSA
Area 0
Command
nssa [ default-route-advertise ] [ no-import-route ] [
no-summary ]
undo nssa
default-cost cost
NSSA
ASBR
RIP