59
•
An NSSA area can import external routes in Type 7 LSAs through the ASBR, but a stub area cannot.
•
A totally NSSA area cannot import inter-area routes but an NSSA area can.
Router types
Router classification
The following are OSPF router types and their positions in the AS:
•
Internal router
—All interfaces on an internal router belong to one OSPF area.
•
Area Border Router (ABR)
—An ABR belongs to more than two areas, one of which must be the
backbone area. It connects the backbone area to a non-backbone area. The connection between
an ABR and the backbone area can be physical or logical.
•
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)
—A router exchanging routing information with
another AS is an ASBR, which may not reside on the border of the AS. It can be an internal router
or an ABR.
Figure 22
OSPF router types
Route types
OSPF prioritize routes into the following levels:
•
Intra-area route
•
Inter-area route
•
Type-1 external route
•
Type-2 external route
