IPA IP 2020 Question 67
A question IPA Japan published in 令和2年度 10月 ITパスポート試験 公開問題 問67, translated into English. ITPEC is based on the same exams.
Which of the following is identified by a port number in TCP/IP?
Explanation
A communication application running on a computer — the port number tells the transport layer which program on the host a packet is for.
An IP address brings a packet to the right computer; TCP or UDP then hands it to the right application by its port number. Well-known server programs listen on fixed ports, for example HTTP on 80, HTTPS on 443 and SMTP on 25, while a client is given a temporary port for each connection. So one computer with one IP address can run a web server, a mail server and a browser at the same time.
Answer (c)
Why not others:
- •(a) — a LAN interface is identified by its MAC address
- •(b) — a computer or device on an IP network is identified by its IP address
- •(d) — a wireless LAN network is identified by its SSID (ESSID)
Key rule: MAC address = interface, IP address = host, port number = application on the host, SSID = wireless LAN.
Networks · AI-written, may contain errors
This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.