Which command checks local usernames for AAA authentication?

The command used to check local usernames for AAA (Authentication, Authorization, and Accounting) authentication is "aaa authentication local." This command specifically configures AAA processes to utilize the locally configured usernames and passwords for authentication purposes.

In a network device, the AAA framework allows for the management of user access and ensures that user credentials are valid before granting access. By specifying "local" within the command, you instruct the device to look into its internal database of users—those defined through the "username" command with associated passwords. This setup is particularly important in scenarios where external servers (such as TACACS+ or RADIUS) are not available or when local user management is preferred for specific network segments.

Understanding this command is crucial for network engineers to effectively secure access to networking devices, ensuring that only authenticated users can log in based on locally defined credentials.