Cisco Certified Network Associate (CCNA) Practice Exam

To configure MD5 authentication on an OSPF router, which command is used to set the key?

1. (config-if)#ip ospf message-digest-key 1 md5 PASSWORD

2. (config-if)#ospf key 1 md5 PASSWORD

3. (config-if)#ip ospf authentication md5 PASSWORD

4. (config)#ip ospf security md5 PASSWORD

The correct answer is: (config-if)#ip ospf message-digest-key 1 md5 PASSWORD

The correct command to configure MD5 authentication for OSPF is indeed the one that specifies the interface configuration mode and includes the `ip ospf message-digest-key` command followed by the key ID and the key in plain text. This command establishes the necessary parameters for the OSPF process to use MD5 hashing for authenticating routing updates between OSPF neighbors. This command structure is required because: 1. **Scope of Configuration**: The command is applied in interface configuration mode, allowing you to specify which OSPF-enabled interface will use the specified MD5 authentication key. 2. **Key ID**: The command specifies a key ID (`1` in this case), which allows for multiple keys to be configured if needed, providing flexibility in key management. 3. **Key Value**: The password (or key) is specified in plaintext, which is necessary for OSPF to authenticate packets that are being sent between routers, ensuring the integrity and authenticity of routing information exchanged. The other options do not follow the correct syntax or context for setting up OSPF MD5 authentication in Cisco devices, either using incorrect commands or being incorrectly scoped for the OSPF configuration. Using the correct command is essential for successfully enabling secure communication