Which command enable ospf authentication on an interface?
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
Explanation:
BD
This question might be incomplete. Both ip ospf authentication message-digest and area 20 authentication
message-digest command enable OSPF authentication through MD5.
Use the ip ospf authentication-key interface command to specify this password. If you enable MD5
authentication with the message-digest keyword, you must configure a password with the ip ospf messagedigest-key interface command.
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
Source: Cisco Official Certification Guide, Implement Routing Update Authentication on OSPF, p.348
To enable authentication for an OSPF area, use the area authentication command in router configuration
mode. To remove an authentication specification of an area or a specified area from the configuration, use the
no form of this command.
area area-id authentication [message-digest]
no area area-id authentication [message-digest]
Read more here
Source: http://www.cisco.com/c/en/us/td/docs/ios/12_2/iproute/command/reference/fiprrp_r/1rfospf.html
An overall guide:
Source: https://supportforums.cisco.com/document/22961/ospf-authentication