Which line in the following OSPF configuration will not be required for MD5 authentication to work?
interface GigabitEthernet0/1
ip address 192.168.10.1 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 CCNA
! router ospf 65000
router-id 192.168.10.1
area 20 authentication message-digest
network 10.1.1.0 0.0.0.255 area 10
network 192.168.10.0 0.0.0.255 area 0
!
A. ip ospf authentication message-digest
B. network 192.168.10.0 0.0.0.255 area 0
C. area 20 authentication message-digest
D. ip ospf message-digest-key 1 md5 CCNA
Correct answer is C
Note: The area authentication message-digest command in this configuration enables authentication for all of the router interfaces in a particular area. You can also use the ip ospf authentication message-digest command under the interface to configure MD5 authentication for the specific interface. This command can be used if a different authentication method or no authentication method is configured under the area to which the interface belongs. It overrides the authentication method configured for the area. This is useful if different interfaces that belong to the same area need to use different authentication methods.
https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13697-25.html
We’re configuring only 1 interface and the ip ospf authentication message-digest command is overriding the area 20 authentication message-digest command so C is not necessary, even more because we’re using only 1 interface so the correct answer should be C
Correct is “A”