Which type of area should you use in an enterprise OSPF deployment if you want to prevent
propagation of type 5 LSAs but still allow the redistribution of external routes?
A.
stub
B.
totally stubby
C.
backbone
D.
NSSA
E.
virtual link
Explanation:
NSSAs
Notice that Area 2 in Figure 11-5 has an ASBR. If this area is configured as an NSSA, it generates
the external LSAs (Type 7) into the OSPF system while retaining the characteristics of a stub area
to the rest of the autonomous system. There are two options for the ABR. First, the ABR for Area 2
can translate the NSSA external LSAs (Type 7) to autonomous system external LSAs (Type 5)
and Hood the rest of the internetwork. Second, the ABR is not configured to convert the NSSA
external LSAs to Type 5 external LSAs, and therefore the NSSA external LSAs remain within the
NSSA.
There is also an NSSA totally stub area. The difference is that the default NSSA has no default
route unless the ABR is explicitly configured to advertise one. The NSSA totally stub area docs
receive a default route.