CREST CPSA Study Guide Exam: Ports, Protocols, and Network Security 150 Multiple-Choice Questions with Answers and Detailed Rationales

CREST CPSA Study Guide Exam: Ports, Protocols, and Network Security
150 Multiple-Choice Questions with Answers and Detailed Rationales
2025-2026


Section 1: Port and Protocol Identification (Questions 1–40)

Question 1
Which port number is assigned to the SSH protocol for secure remote administration?

A) Port 21
B) Port 22
C) Port 23
D) Port 25
E) Port 443

Correct Answer: B) Port 22

Rationale: SSH (Secure Shell) operates on TCP port 22 by default. It provides encrypted remote
administration and secure file transfer capabilities. Port 21 is FTP, port 23 is Telnet
(unencrypted), port 25 is SMTP, and port 443 is HTTPS.

Question 2
What service runs on TCP port 21?

A) SSH
B) Telnet
C) FTP
D) SMTP
E) HTTP

Correct Answer: C) FTP

Rationale: FTP (File Transfer Protocol) uses TCP port 21 for command/control channel
communication. Data transfer occurs on port 20. SSH uses port 22, Telnet port 23, SMTP port
25, and HTTP port 80.

Question 3
Which protocol operates on UDP port 53?

,A) HTTP
B) FTP
C) DNS
D) DHCP
E) SNMP

Correct Answer: C) DNS

Rationale: DNS (Domain Name System) uses both TCP and UDP port 53. UDP is used for
standard queries where responses are small enough to fit in a single packet, while TCP is used
for zone transfers and large responses.

Question 4
What is the default port for HTTPS?

A) Port 80
B) Port 443
C) Port 8080
D) Port 8443
E) Port 21

Correct Answer: B) Port 443

Rationale: HTTPS (HTTP Secure) uses TCP port 443 by default. HTTP uses port 80. Port 8080 is
commonly used as an alternative HTTP port, and port 8443 is often used as an alternative
HTTPS port.

Question 5
SMTP is associated with which port number?

A) Port 110
B) Port 143
C) Port 25
D) Port 993
E) Port 995

Correct Answer: C) Port 25

Rationale: SMTP (Simple Mail Transfer Protocol) uses TCP port 25 for sending emails. Port 110 is
POP3, port 143 is IMAP, port 993 is IMAPS, and port 995 is POP3S.

Question 6
Which protocol runs on UDP port 161?

,A) SSH
B) SNMP
C) SMTP
D) DNS
E) DHCP

Correct Answer: B) SNMP

Rationale: SNMP (Simple Network Management Protocol) uses UDP port 161 for agent
communication. SNMP trap messages use UDP port 162. SSH uses port 22, SMTP port 25, DNS
port 53, and DHCP uses ports 67 and 68.

Question 7
What service uses TCP port 23?

A) SSH
B) FTP
C) Telnet
D) SMTP
E) HTTP

Correct Answer: C) Telnet

Rationale: Telnet uses TCP port 23 for unencrypted remote terminal access. It is considered
insecure because it transmits credentials and data in cleartext, making it vulnerable to
eavesdropping.

Question 8
Which port is used by POP3?

A) Port 25
B) Port 110
C) Port 143
D) Port 993
E) Port 995

Correct Answer: B) Port 110

Rationale: POP3 (Post Office Protocol version 3) uses TCP port 110 for retrieving emails from a
mail server. Port 143 is IMAP, port 993 is IMAPS (IMAP over SSL), and port 995 is POP3S (POP3
over SSL).

Question 9
NTP operates on which port?

, A) Port 53
B) Port 67
C) Port 123
D) Port 161
E) Port 443

Correct Answer: C) Port 123

Rationale: NTP (Network Time Protocol) uses UDP port 123 to synchronize computer clocks over
networks. Accurate time synchronization is critical for security logging, certificate validation, and
authentication protocols.

Question 10
What service is associated with port 3389?

A) SSH
B) Telnet
C) RDP
D) VNC
E) FTP

Correct Answer: C) RDP

Rationale: RDP (Remote Desktop Protocol) uses TCP port 3389 for remote desktop connections
to Windows systems. SSH uses port 22, Telnet port 23, VNC typically uses port 5900, and FTP
uses port 21.

Question 11
Which port is used by Kerberos authentication?

A) Port 53
B) Port 88
C) Port 389
D) Port 443
E) Port 636

Correct Answer: B) Port 88

Rationale: Kerberos uses both TCP and UDP port 88 as a network authentication protocol that
allows secure communication over non-secure networks using ticket-based authentication.

Question 12
DHCP servers listen on which UDP ports?