HP HPE FlexNetwork 7500 series, Руководство по настройке

Страница: 80 / 592

68
routes. It advertises a default route in a Type-3 LSA so that the routers in the area can reach external
networks through the default route.
NSSA area and totally NSSA 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.
As shown in Figure 20 , the OSPF AS contains Area 1, Area 2, and Area 0. The other two ASs run RIP.
Area 1 is an NSSA area where the ASBR redistributes RIP routes in Type-7 LSAs into Area 1. Upon
receiving the Type-7 LSAs, the NSSA ABR translates them to Type-5 LSAs, and 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 Type-5 LSAs because it is an NSSA area.
Figure 20 NSSA area
Router types
OSPF routers are classified into the following types based on their positions in the AS:
•
Internal router —All interfaces on an internal router belong to one OSPF area.
•
ABR —Belongs to more than two areas, one of which must be the backbone area. ABR
connects the backbone area to a non-backbone area. An ABR and the backbone area can be
connected through a physical or logical link.
•
Backbone router —No less than one interface of a backbone router must reside in the
backbone area. All ABRs and internal routers in Area 0 are backbone routers.
•
ASBR —Exchanges routing information with another AS is an ASBR. An ASBR might not reside
on the border of the AS. It can be an internal router or an ABR.
NSSA
Area 2
Type 7 Type 5
Type 5
Type 5
Type 5
Area 0 Area 1
NSSA
ABR
ABR
NSSA
ASBR
ASBR
RIP
RIP