HP MSR2000 series Configuration Manual page 71

To configure an area as a totally stub area, the stub command must be configured on routers in the
•
area, and the ABR of the area must be configured with the stub [ no-summary ] command.
A totally stub area cannot have an ASBR because AS external routes cannot be distributed into the
•
stub area.
Virtual links cannot transit totally stub areas.
•
NSSA area
Similar to a stub area, an NSSA area does not import AS external LSAs (Type-5 LSAs), but can import
Type-7 LSAs generated by the NSSA ASBR. The NSSA ABR translates Type-7 LSAs into Type-5 LSAs and
advertises the Type-5 LSAs to other areas.
In the following figure, the OSPF AS contains Area 1, Area 2, and Area 0. The other two ASs run RIP.
Area 1 is an NSSA area. The ASBR redistributes RIP routes in Type-7 LSAs into Area 1. Upon receiving
these Type-7 LSAs, the NSSA ABR translates them to Type-5 LSAs, and then advertises the Type-5 LSAs to
Area 0.
The ASBR of Area 2 redistributes RIP routes in Type-5 LSAs into the OSPF routing domain. However, Area
1 does not receive these Type-5 LSAs because it is an NSSA area.
Virtual links cannot transit NSSA areas.
Figure 20 NSSA area
Comparison between the areas
Figure 21 Comparison between the areas
A Type 3 default route
can be distributed in the
area, while Type 3 and
Type 5 LSAs cannot be
distributed in the area
Totally Stub
area
Permits
Type 3 LSAs
Figure 21 shows the comparison of the areas:
• In a totally stub area, the ABR distributes a Type 3 default route, rather than external routes and
inter-area routes.
A stub area can import inter-area routes, but a stub area cannot.
•
Stub area
NSSA area
Permits
Type 7 LSAs
within the area
Does not
permit Type 3
58
Totally NSSA
area
LSAs