Which service is denoted by TCP/UDP port number 53?

A.
Domain Name Service (DNS)

B.
File Transfer Protocol (FTP)

C.
Telnet

D.
HTTP

Explanation:
Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) port number 53 is assigned to
Domain Name Service (DNS), which is used to convert hostnames into Internet Protocol (IP) addresses.
Some common TCP and UDP port number assignments are as follows:
port 25: Assigned to Simple Mail Transfer Protocol (SMTP), a TCP protocol used to send and receive e-mail
messages.
port 23: Assigned to Telnet to allow remote logins and command execution.
port 21: Assigned to File Transfer Protocol (FTP). It is used to control FTP transmissions. Port number 20 is
also used by FTP for FTP data.
port 80: Assigned to Hypertext Transfer Protocol (HTTP), which is the base for transferring Web pages over
the Internet.Objective:
Infrastructure Security
Sub-Objective:
Configure, verify, and troubleshoot IPv4 and IPv6 access list for traffic filtering

Internetworking Technology Handbook > Internetworking Basics > OSI Model and Communication Between
Systems>Multiplexing Basics