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LFCS · Question #52

What is true regarding TCP port 23?

The correct answer is A. Port 23 is the well known port for the telnet service which is a plain text protocol that should no. TCP port 23 is the well-known port for the Telnet service, an unencrypted protocol that transmits data in plain text, making it insecure for sensitive communications.

Submitted by salim_om· Apr 18, 2026Networking

Question

What is true regarding TCP port 23?

Options

  • APort 23 is the well known port for the telnet service which is a plain text protocol that should no
  • BPort 23 is the well known port for the SSH service which provides secure logins.
  • CPort 23 is the well known port for the rlogin service which is SSL secured by default.
  • DPort 23 is the well known port for the system login services which are encrypted when the user

How the community answered

(35 responses)
  • A
    89% (31)
  • B
    3% (1)
  • C
    6% (2)
  • D
    3% (1)

Why each option

TCP port 23 is the well-known port for the Telnet service, an unencrypted protocol that transmits data in plain text, making it insecure for sensitive communications.

APort 23 is the well known port for the telnet service which is a plain text protocol that should noCorrect

Port 23 is indeed the well-known port assigned to the Telnet service, which is a legacy protocol that transmits all data, including login credentials, in plain text without encryption, making it vulnerable to eavesdropping and thus generally unsafe for modern use.

BPort 23 is the well known port for the SSH service which provides secure logins.

The SSH (Secure Shell) service uses TCP port 22, not 23, and provides secure, encrypted communication for remote logins.

CPort 23 is the well known port for the rlogin service which is SSL secured by default.

The rlogin service typically uses TCP port 513 and is not SSL secured by default; it is another older, unencrypted protocol.

DPort 23 is the well known port for the system login services which are encrypted when the user

While Telnet provides system login services, it does so unencrypted; secure login services, such as SSH, use different ports and provide encryption.

Concept tested: Well-known TCP ports and service security

Source: https://www.iana.org/assignments/port-numbers/port-numbers.xhtml

Topics

#TCP Ports#Telnet#Network Protocols#Security Basics

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