What is the typical first global command to enable AAA on a Cisco router?

The command aaa new-model is the foundational command to enable AAA (Authentication, Authorization, and Accounting) services on a Cisco router. Without this command, other AAA-related configurations, such as authentication methods or server groups, will not function. It essentially activates the AAA framework. aaa enable is not a valid Cisco IOS command. aaa server-group is used to define a group of AAA servers (e.g., RADIUS or TACACS+), but it requires aaa new-model to be active first. aaa authentication login defines how users authenticate for login access, but it also depends on aaa new-model being configured.