令和2年度 ITパスポート試験問67

This question's explanation and your answers so far.

問67

頻出度★★☆

TCP/IP におけるポート番号によって識別されるものはどれか。

出典　令和2年度 ITパスポート試験問67

解説

問 67

Incorrectア
The LAN interface of a device connected to a LAN is identified by a MAC address (physical address), not by a port number.
Incorrectイ
A computer or communication device connected to an IP network is itself identified by an IP address, not by a port number.
ウ
正解 In TCP/IP communication, the device at the other end is identified by its IP address, while which communication application (service) inside that device is identified by a port number. On a single computer, multiple applications such as Web and email communicate at the same time, so an IP address alone cannot uniquely determine the destination. Each application is therefore assigned a port number (for example, HTTP=80, HTTPS=443), and incoming packets are sorted to the correct application. Thus what a port number identifies is a communication application running on a computer, so option ウ is correct.
Incorrectエ
A wireless LAN network is identified by an SSID (ESSID), which is unrelated to port numbers.

ここがポイント

A port number is a number (0–65535) used to distinguish among the multiple communication applications (processes) running within a single device. An IP address specifies which device, and a port number specifies which application on that device.
Summary of what each one identifies: MAC address → LAN interface (device); IP address → device on the network; port number → communication application; SSID → wireless LAN network.

用語

解答問67ウ