問92
頻出度★★☆
インターネットに接続されているサーバが, 1台でメール送受信機能とWebアクセス機能の両方を提供しているとき, 端末のアプリケーションプログラムがそのどちらの機能を利用するかをサーバに指定するために用いるものはどれか。
令和6年度 ITパスポート試験 問92
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 92
Incorrectア
An IP address is a number for uniquely identifying a device (server) itself on a network; although it tells you which device it is, it cannot distinguish whether to use the email function or the Web function inside that device. Therefore it is incorrect.
Incorrectイ
A domain is a name that represents the scope of an organization or network on the Internet; ultimately it maps to an IP address and is used to identify a server. It does not play the role of specifying the individual services within a server, so it is incorrect.
- ウ
正解 When a single server provides multiple services (email send/receive and Web access) at the same time, the server itself can be identified by its “IP address,” but which service to use within it is specified by the “port number.” A port number identifies each application (service) running inside a host; for example, Web (HTTP) is 80, email sending (SMTP) is 25, and email receiving (POP3) is 110, with a number assigned to each service. The terminal designates the server by the destination IP address and tells the server “which function it wants to use” by the port number, so the correct answer is ウ.
Incorrectエ
A host name is a name given to a server (host); it is converted into an IP address by DNS and used to identify a device. This too only indicates which server it is, and cannot specify which service to use within the same server, so it is incorrect.
ここがポイント
- A port number is a number used to identify multiple services (applications) running on the same host (IP address). Typical examples: HTTP=80, SMTP=25, POP3=110.
- Understand the layering clearly: a communication destination is determined by the pair of IP address (which device) plus port number (which service on that device).
用語