SK0-004 · Question #826
A server technician is enforcing server hardening on Telnet ports in DMZ-facing servers. Which of the following ports should the technician block on the company firewall?
The correct answer is B. 23. Telnet uses TCP port 23, which must be blocked on the firewall to prevent unencrypted remote access to DMZ-facing servers.
Question
A server technician is enforcing server hardening on Telnet ports in DMZ-facing servers. Which of the following ports should the technician block on the company firewall?
Options
- A22
- B23
- C123
- D143
How the community answered
(20 responses)- A5% (1)
- B95% (19)
Why each option
Telnet uses TCP port 23, which must be blocked on the firewall to prevent unencrypted remote access to DMZ-facing servers.
Port 22 is used by SSH, the secure replacement for Telnet, and blocking it would disable encrypted remote administration rather than harden against Telnet.
Telnet is assigned TCP port 23 by IANA and transmits all data including credentials in plaintext. Blocking port 23 on the firewall prevents Telnet sessions from being established to DMZ-facing servers, which is a standard server hardening practice since the protocol provides no encryption or integrity protection.
Port 123 is used by the Network Time Protocol (NTP) for clock synchronization and has no relation to Telnet.
Port 143 is used by IMAP for email retrieval and is unrelated to Telnet remote access.
Concept tested: Telnet port number and server hardening
Source: https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml
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