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Networking — A+ Core 1 practice questions

Domain 2 of the CompTIA A+ Core 1 (220-1101) exam. 187 questions on this domain in the full bank — here are four free samples with answers and explanations.

Question 1 · Difficulty 2/5

Which port number does the Trivial File Transfer Protocol (TFTP) use by default? (Select the best answer.)
  1. UDP 69
  2. TCP 21
  3. UDP 67
  4. TCP 20
Show answer & explanation

Correct answer: A

UDP 69
TFTP uses UDP port 69 by default. It relies on UDP because it is a lightweight protocol with no connection establishment, authentication, or error recovery beyond basic retransmission. TCP 21 is the FTP control port, TCP 20 is the FTP data port, and UDP 67 is the DHCP server port; none of these are associated with TFTP.

Question 2 · Difficulty 3/5

A mail server administrator is configuring a client mail application to submit outbound email from authenticated end users to the company's mail server. The administrator wants to use the port designated specifically for authenticated message submission rather than the traditional unauthenticated relay port. Which port should the administrator configure the client to use? (Select the best answer.)
  1. TCP 25
  2. TCP 587
  3. UDP 53
  4. TCP 110
Show answer & explanation

Correct answer: B

TCP 587
TCP 587 is the SMTP submission port defined in RFC 6409, intended for authenticated end-user mail clients submitting messages to their outbound mail server. TCP 25 is the traditional SMTP relay port used for server-to-server mail transfer; it does not enforce authentication and is commonly blocked by ISPs to prevent spam. UDP 53 is the DNS query port, unrelated to mail delivery. TCP 110 is the POP3 port used for mail retrieval, not submission.

Question 3 · Difficulty 2/5

Which port does the File Transfer Protocol (FTP) use by default for its control connection? (Select the best answer.)
  1. TCP 20
  2. TCP 21
  3. TCP 22
  4. UDP 69
Show answer & explanation

Correct answer: B

TCP 21
FTP uses TCP 21 for the control connection, which carries commands and responses between the client and server. TCP 20 is the data connection port used during active-mode FTP file transfers, not the control channel. TCP 22 is the default port for SSH, a separate protocol. UDP 69 is the port for TFTP, which is an entirely different file transfer protocol that uses no control channel.

Question 4 · Difficulty 3/5

A newly provisioned workstation powers on and has no IP address configuration. The workstation broadcasts a DHCPDISCOVER message to obtain an address. Which source and destination UDP port numbers are used in that initial broadcast packet? (Select the best answer.)
  1. Source UDP 67, destination UDP 68
  2. Source UDP 68, destination UDP 67
  3. Source UDP 69, destination UDP 67
  4. Source UDP 68, destination UDP 69
Show answer & explanation

Correct answer: B

Source UDP 68, destination UDP 67
In the DHCP exchange defined by RFC 2131, the client sends from its own port UDP 68 and addresses the server at UDP 67. The roles are asymmetric: UDP 67 is the server-side (listening) port and UDP 68 is the client-side (source) port. Reversing these (source 67, destination 68) describes traffic flowing from a DHCP server back to the client, not the initial DHCPDISCOVER. UDP 69 is the TFTP port and is unrelated to DHCP address assignment.

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