Chapter 19. Interface Configuration Commands
ip ospf authentication
ip ospf authentication authentication-key password
ip ospf authentication message-digest
Command 19-3 requires the use of command 19-11 (ip ospf message-digest-key key-id md5 password).
ip ospf authentication null
key-id—. Key used to identify the password. Range of values is 1 to 255. Both ends of a link must use the same key and password.
password—. Password to be used for authentication in the selected area on the selected interface. The password is an alphanumeric string from 1 to 8 characters.
Purpose: In IOS versions before 12.0, if authentication was enabled for an OSPF area, then all interfaces in the area had to be configured with the same authentication type. ...