CCNP Infrastructure Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  Configure the neighbor with the command area 0 authentication message-digest.

  Why it's wrong here

  Area authentication enables authentication for all interfaces in the area, but the first router has interface-level authentication configured. If the neighbor uses area authentication, it might still work if the keys match, but it is not the required additional configuration. The question asks for the additional configuration on the neighbor to match the interface-level MD5 authentication.

• ✗

  Configure the neighbor with the command ip ospf authentication-key Cisco123.

  Why it's wrong here

  The 'ip ospf authentication-key' command is used for plain text (simple password) authentication, not MD5. Since the engineer configured MD5 on the first router, the neighbor must also use MD5 with the same key. Using plain text authentication would cause a mismatch and prevent adjacency.

• ✓

  Configure the same key ID and password on the neighbor's interface with ip ospf message-digest-key 1 md5 Cisco123.

  Why this is correct

  For OSPF MD5 authentication to succeed, both routers must have the same key ID and password configured on their interfaces. The neighbor must have the identical message-digest-key command with the same key number and MD5 password. Without this matching configuration, authentication will fail, and the adjacency will not form.

• ✗

  Configure the neighbor with the command ip ospf authentication null.

  Why it's wrong here

  The 'ip ospf authentication null' command disables authentication on the interface. Since the first router is using MD5 authentication, disabling authentication on the neighbor would cause a mismatch and prevent adjacency. The neighbor must use the same authentication type and key.