Which of the following authentication methods was designed to be used primarily for administration purposes, such as giving users access to manage switches and routers?

RADIUS (Remote Authentication Dial-In User Service) provides centralized Authentication, Authorization, and Accounting (AAA) for users connecting to network services. It is the standard protocol used by network administrators to control and audit access to managed devices such as switches and routers, making it the primary choice for infrastructure device administration.

LDAP (Lightweight Directory Access Protocol) is a protocol for querying and modifying directory services such as Active Directory, and is not designed as an authentication mechanism for managing network device access.

TACACS (Terminal Access Controller Access-Control System) is an older AAA protocol that predates RADIUS and has been largely replaced; its successor TACACS+ provides similar functionality but RADIUS is the identified standard answer for this use case.

Active Directory is a Microsoft directory service and identity platform, not a standalone authentication protocol, and it is not independently deployed to manage access to switches and routers.