What happens if the TACACS+ server is available and rejects the user’s credentials in a Junos OS device?

When a TACACS+ server is available and it rejects the user's credentials on a Junos OS device, the user is not allowed to access the device. This is because TACACS+ is designed to provide centralized access control, and if the server denies access based on authentication failure, it will prevent the user from logging in to the device entirely.

In environments that utilize TACACS+, the default behavior is to strictly adhere to the authentication results provided by the TACACS+ server. If a user's credentials do not match those stored on the server, access is denied, ensuring that only authorized users can gain entry to the system.

Other choices propose scenarios that do not apply in this situation. For instance, limited access would only occur if the server allowed some form of access based on roles or permissions, and attempting connections to another TACACS+ server happens only if specified in the configuration and only after the local database has been checked. In this case, since the focus is on a rejected user credential scenario, denial of access is the definitive outcome.