問60
頻出度★★☆
インターネットのファイル転送で使用される anonymous FTP に関する記述として, 適切なものはどれか。
平成24年度 春期 ITパスポート試験 問60
テクノロジ系ネットワーク › 通信プロトコル
This question's explanation and your answers so far.
解説
問 60
Incorrectア
“It is a protocol that adds encryption functionality to FTP” describes FTPS (FTP over SSL/TLS), or SFTP, which uses the mechanism of SSH; these are different things from anonymous FTP. What anonymous FTP specifies is the authentication and operating method of who is accepted at login, not the encryption of the content of communication. On the contrary, ordinary anonymous FTP exchanges both the ID and the data in plain text, so note that it is not encrypted.
Incorrectイ
“It is a method that uses the protocol for Web communication” describes downloading files with HTTP/HTTPS, so it is wrong. Anonymous FTP always uses FTP, a protocol dedicated to file transfer. The question itself says “anonymous FTP, which is used for file transfer over the Internet,” and as the name shows, it is one form of FTP.
- ウ
正解 The correct answer is ウ. Anonymous FTP is a way of operating an FTP server so that files can be made available to the general public over the Internet: you can connect simply by specifying the fixed name anonymous or ftp as the user ID. Normally FTP works by registering an account on the server and authenticating with an ID and password that belong to that user alone before connecting, but with anonymous FTP even someone who has no user-specific password can log in. When a password is requested, it is customary to enter your own e-mail address, but this is only a formality for recording where the connection came from, and it is not checked for correctness. In other words, the wording of choice ウ, “an FTP that does not use a user-specific password and can be used by anyone,” is exactly the definition of anonymous FTP. It has long been widely used by sites that distribute free software and sites that offer various public documents for download, and it is normally operated so that only the public directory is readable while access to other areas is restricted.
Incorrectエ
“It is a lightweight and simple protocol that has neither user authentication functionality nor error correction functionality during communication” describes TFTP (Trivial File Transfer Protocol), so it is wrong. TFTP uses UDP, has no authentication mechanism, and is a simplified file transfer protocol used for transferring configuration files and firmware for network devices. Anonymous FTP, by contrast, is FTP itself (it uses TCP and performs reliable transfer), not a separate lightweight protocol. Moreover, in anonymous FTP the procedure of entering an ID and logging in does exist; its characteristic is that the common name anonymous is used as that ID.
ここがポイント
- Anonymous FTP = a way of operating an FTP server for public access in which specifying “anonymous” (or “ftp”) as the user ID lets the general public connect even without a user-specific password. It is customary to enter an e-mail address in the password field, but it is not verified.
- Telling confusable file-transfer terms apart: FTPS = FTP with SSL/TLS encryption added, SFTP = a separate protocol that transfers files encrypted over SSH, HTTP / HTTPS = protocols for Web communication, TFTP = a lightweight, simple UDP-based file transfer protocol with no authentication functionality.
用語