2.1 - Common ports and protocols

CompTIA A+ Core 1 objective 2.1 is about memorising common network ports and the protocols that use them. HTTPS uses port 443 to serve encrypted web traffic, while plain HTTP uses 80. DNS uses port 53 for standard name-resolution queries. SMTP sends email on port 25. Other exam favourites include FTP (20/21), SSH (22), Telnet (23), DHCP (67/68), RDP (3389) and SMB (445). This objective rewards pure recall - you either know the number or you don't - so flashcards and memory hooks help most. Expect direct questions that give a protocol and ask its port, or give a port and ask which service runs there, sometimes wrapped in a short scenario about a blocked or misconfigured service. There is no shortcut here beyond memorisation, so drill the numbers until they are automatic.

Memory hook
HTTPS 443, HTTP 80, DNS 53, SMTP 25, FTP 20/21, SSH 22, Telnet 23, DHCP 67/68, RDP 3389, SMB 445. Pure recall - drill these with flashcards.

Practice questions

1. Which transport protocol is connection-oriented and guarantees delivery?

  • UDP
  • TCP (correct answer)
  • ICMP
  • ARP

TCP establishes a connection (3-way handshake) and retransmits lost data. UDP is connectionless/best-effort.

2. Which port does RDP use for remote desktop sessions?

  • Port 22
  • Port 443
  • Port 3389 (correct answer)
  • Port 161

RDP uses TCP 3389. SSH=22, HTTPS=443, SNMP=161.

3. Which TCP port does HTTPS use by default?

  • Port 80
  • Port 443 (correct answer)
  • Port 22
  • Port 53

HTTPS (HTTP secured with TLS) uses TCP port 443. HTTP uses 80, SSH 22, and DNS 53.

4. Which port does the SMTP protocol use to SEND email?

  • 110
  • 25 (correct answer)
  • 143
  • 53

SMTP uses port 25 to send mail. POP3 (110) and IMAP (143) retrieve mail; DNS uses 53.

5. Which protocol provides a secure, encrypted command-line connection to a remote device?

  • Telnet (23)
  • SSH (22) (correct answer)
  • FTP (21)
  • HTTP (80)

SSH (port 22) encrypts remote CLI sessions. Telnet (23) is the insecure, cleartext equivalent.

6. Which ports does SMB/CIFS use for Windows file and printer sharing?

  • TCP port 22 (SSH)
  • TCP port 53 (DNS)
  • TCP 445 (and 137-139) (correct answer)
  • TCP port 3389 (RDP)

SMB uses TCP 445 (legacy NetBIOS 137-139). It's how Windows shares files/printers.

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