Which file transfer protocol requires authentication to upload a router backup configuration to a remote server?

FTP (File Transfer Protocol) requires authentication (username and password) for both uploading and downloading files, making it suitable for secure transfers like router backup configurations. SMTP (Simple Mail Transfer Protocol) is used for sending email, not file transfers. TFTP (Trivial File Transfer Protocol) is a simpler protocol that typically does not require authentication, making it less secure for sensitive data like configuration files. DTP (Dynamic Trunking Protocol) is a Cisco proprietary protocol used for negotiating trunking on a link, unrelated to file transfers.