Area Border Router (ABR) is a router located on the border of one or more OSPF areas that
connect those areas to the backbone network. An ABR will inject a default route into which two
types of areas? (Choose two.)
A.
Area 0
B.
NSSA
C.
Totally stubby
D.
Stub
Explanation:
Totally Stub Areas: These areas do not allow routes other than intra-area and the default routes to
be propagated within the area. The ABR injects a default route into the area and all the routers
belonging to this area use the default route to send any traffic outside the area.
Stub Areas: These areas do not accept routes belonging to external autonomous systems (AS);
however, these areas have inter-area and intra-area routes. In order to reach the outside
networks, the routers in the stub area use a default route which is injected into the area by the
Area Border Router (ABR). A stub area is typically configured in situations where the branch office
need not know about all the routes to every other office, instead it could use a default route to the
central office and get to other places from there. Hence the memory requirements of the leaf node
routers is reduced, and so is the size of the OSPF database.