Router Types - HPE FlexNetwork HSR6800 Configuration Manual

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
A Not-So-Stubby Area (NSSA) area does not import AS external LSAs (Type-5 LSAs) but it 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.
You can configure an NSSA area as a totally NSSA area. The ABR of a totally NSSA area does no
advertise inter-area routes or external 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.
In Figure 18, 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
these 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. Area 1
cannot receive these Type-5 LSAs because it is an NSSA area.
Figure 18 NSSA area

Router types

OSPF classifies routers into the following types based on their positions in the AS:
•
Internal router—All interfaces on an internal router belong to one OSPF area.
•
Area Border Router (ABR)—Belongs to more than two areas, one of which must be the
backbone area. An 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—At least one interface of a backbone router must reside in the backbone
area. All ABRs and internal routers in area 0 are backbone routers.
•
Autonomous System Boundary Router (ASBR)—Exchanges routing information with
another AS. An ASBR might not reside on the border of the AS. It can be an internal router or an
ABR.
58