Which two options are valid checks that should be performed first to verify proper OSPF operation?

You are troubleshooting an OSPF problem where external routes are not showing up in the OSPF
database. Which two options are valid checks that should be performed first to verify proper OSPF
operation? (Choose two.)

A.
Are the ASBRs trying to redistribute the external routes into a totally stubby area?

B.
Are the ABRs configured with stubby areas?

C.
Is the subnets keyword being used with the redistribution command?

D.
Is backbone area (area 0) contiguous?

E.
Is the CPU utilization of the routers high?

Explanation:
A totally stubby stubby area cannot have an ASBR so it will discard this type of LSA (LSA Type 5)
-> A is a valid check.
Each stubby area needs an ABR to communicate with other areas so it is normal -> B is not a
valid check.
When pulling routes into OSPF, we need to use the keyword “subnets” so that subnets will be
redistributed too. For example, if we redistribute these EIGRP routes into OSPF:
+ 10.0.0.0/8+ 10.10.0.0/16+ 10.10.1.0/24

without the keyword “subnets”
router ospf 1redistribute eigrp 1
Then only 10.0.0.0/8 network will be redistributed because other routes are not classful routes,
they are subnets. To redistribute subnets we must use the keyword “subnets”
router ospf 1redistribute eigrp 1 subnets
-> C is a valid check.
We don’t need to care if area 0 is contiguous or not -> D is not a valid check.
CPU utilization cannot be the cause for this problem -> E is not a valid check.