The login method is configured on the VTY lines of a router with these parameters
* The first method for authentication it TACACS
* If TACACS is unavailable login is allowed without any provided credentials Which configuration accomplishes this task?

Correct Answer: C
The correct configuration for the scenario described is to use TACACS for authentication, and if TACACS is unavailable, allow login without any credentials. This is achieved by the command aaa authentication login default group tacacs+ none, which specifies TACACS as the primary authentication method and none as the secondary method, meaning no authentication is required if TACACS is not available.
References: The information is based on the Implementing and Operating Cisco Service Provider Network Core Technologies (SPCOR) training