Into which two types of areas would an area border router (ABR) inject a default route? (Choose two.)
Select 2 response(s).
A.
the autonomous system of a different interior gateway protocol (IGP)
B.
area 0
C.
totally stubby
D.
NSSA
E.
stub
F.
the autonomous system of an exterior gateway protocol (EGP)
Answer: C E
Explanation
Both stub area & totally stubby area allow an ABR to inject a default route. The main difference between these 2 types of areas is:
+ Stub area replaces LSA Type 5 (External LSA – created by an ASBR to advertise network from another autonomous system) with a default route
+ Totally stubby area replaces both LSA Type 5 and LSA Type 3 (Summary LSA – created by an ABR to advertise network from other areas, but still within the AS, sometimes called interarea routes) with a default route.
Below summarizes the LSA Types allowed and not allowed in area types:
Area Type Type 1 & 2 (within area) Type 3 (from other areas) Type 4 Type 5 Type 7
Standard & backbone Yes Yes Yes Yes No
Stub Yes Yes No No No
Totally stubby Yes No No No No
NSSA Yes Yes No No Yes
Totally stubby NSSA Yes No No No Yes
0
0
Hi Cesar good comment,
To make it clear, this is what it means:
Backbone: LSA type 1,2,3,4,5
Stub: LSA type 1,2,3
Totally Stub: LSA type 1,2
NSSA: LSA type 1,2,3,7
Totally NSSA: LSA type 1,2,7
0
0
An ABR is a router located on the border of one or more OSPF areas that normally
connect those areas to the backbone network (keep in mind the virtuals links).
The ABR injects the default route in the areas (no in the backbone) with a LAS type 3 (be carefull, an ASBR use to originate a default route into an area a LSA type 5)
Apparently the answers: totally stubby, NSSA and stub, are right but there are two areas where the ABR does not inject default route, standard and NSSA. It means that the correct answers are C and E,
Note: to generate a default route on a standard, you must use the default-information originate command and it will be created as a LSA type 5.
0
0