NodnGroup ports by job
- Remote access: 22 SSH, 23 Telnet, 3389 RDP
- Email: 25 SMTP sends; 110 POP3 and 143 IMAP retrieve
- Web: 80 HTTP, 443 HTTPS
- Network services: 53 DNS, 67/68 DHCP
- Files and directories: 20/21 FTP, 137–139 NetBIOS, 389 LDAP, 445 SMB
Study guide · Flashcards & memory notes
CompTIA A+ Flashcards & Memory Notes
40 recall cards for the facts CompTIA A+ questions depend on: port numbers, addressing, RAID, hypervisors, Windows and Linux commands, malware removal, and security basics. Study one card at a time or browse every answer below.
How to use these cards: Say the answer out loud before you flip the card, and mark it honestly. Revisit the cards you missed tomorrow rather than rereading them right away. Progress is kept only while this page is open. For the full explanations behind each card, see the core notes.
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Deck 1 · Core 1: Networking ports and protocols
Port numbers, transport protocols, and what each service does.
1.1Which port does SSH use, and which insecure protocol did it replace?
TCP port 22, SSH (Secure Shell). It replaced Telnet (port 23), which sends everything, including passwords, in plain text.
Memory note: SSH has two S's, so think 2-2. Telnet is the very next port, 23.
1.2Which ports and transport protocol does DHCP use?
UDP 67 (server) and UDP 68 (client).
Memory note: A new client has no IP address yet, so it broadcasts a DHCP Discover message. TCP cannot broadcast, so DHCP must use UDP. The server gets the lower number.
1.3What is the difference between POP3 (port 110) and IMAP (port 143)?
- POP3 (110): downloads mail to a single device and usually removes it from the server.
- IMAP (143): keeps mail on the server and synchronizes folders across multiple devices.
Memory note: Use IMAP for a user with a phone, a laptop, and a desktop. The TLS versions are POP3S on 995 and IMAPS on 993.
1.4Which protocol uses TCP port 445 for Windows file and printer sharing?
SMB (Server Message Block), also called CIFS.
Memory note: NetBIOS over TCP/IP (ports 137–139) is the legacy way Windows shared files; modern SMB runs directly on 445.
1.5What port does RDP use, and what does it provide?
Port 3389 (TCP and UDP). It provides a full graphical remote desktop session to a Windows computer.
Memory note: Windows Home editions can connect to other computers but cannot host incoming RDP sessions. Pro or higher is required.
1.6Which protocol and port send email between mail servers?
SMTP on TCP port 25.
Memory note: SMTP sends; POP3 and IMAP retrieve.
1.7Which port does DNS use, and when does it use TCP instead of UDP?
Port 53. Most lookups use UDP. DNS uses TCP for zone transfers between servers and for responses too large for UDP.
1.8What is the difference between FTP ports 20 and 21?
Port 21 carries control commands, and port 20 carries the data transfer.
Memory note: FTP is unencrypted. For secure transfers, use SFTP, which runs over SSH on port 22.
1.9Which port does LDAP use, and what is it for?
Port 389. LDAP queries and updates directory services such as Active Directory.
Memory note: LDAP over TLS (LDAPS) uses port 636.
1.10What is the difference between ports 80 and 443?
Port 80 is unencrypted HTTP. Port 443 is HTTPS, which encrypts web traffic with TLS.
Memory note: Do not confuse 443 (HTTPS) with 445 (SMB file sharing).
Deck 2 · Core 1: Hardware, networking, and cloud
Addressing, storage, memory, wireless, power, and virtualization.
2.1What is the IPv4 APIPA range, and when is an APIPA address assigned?
169.254.0.1 to 169.254.255.254 (169.254.0.0/16). The operating system assigns one automatically when the client cannot get a response from a DHCP server.
Memory note: A 169.254.x.x address points to a DHCP problem: check the cable, the switch port, and the DHCP server or scope.
2.2What is the IPv6 equivalent of an IPv4 APIPA address?
A link-local address, which uses the prefix fe80::/10.
Memory note: Every IPv6 interface has a link-local address, even when a global address is also assigned.
2.3Compare RAID 0, 1, 5, 6, and 10: minimum drives and fault tolerance.
- RAID 0: minimum 2 drives; no fault tolerance (striping for speed).
- RAID 1: minimum 2 drives; survives one failure in a two-drive mirror.
- RAID 5: minimum 3 drives; survives one failure (distributed parity).
- RAID 6: minimum 4 drives; survives two failures (dual parity).
- RAID 10: minimum 4 drives; survives one failure per mirrored pair.
Memory note: Minimum drives 2-2-3-4-4. RAID is not a backup.
2.4Which memory technology detects and corrects single-bit RAM errors in real time?
ECC (error-correcting code) RAM. It requires a compatible motherboard and CPU and is common in servers and workstations.
Memory note: DDR5 on-die ECC works only inside each memory chip. A standard DDR5 module is not ECC RAM.
2.5What is the main structural difference between a Type 1 and a Type 2 hypervisor?
- Type 1 (bare metal): installs directly on the hardware with no host operating system, such as VMware ESXi, Microsoft Hyper-V, or Proxmox VE.
- Type 2 (hosted): runs as an application inside an existing operating system, such as Oracle VirtualBox or VMware Workstation.
Memory note: Type 1 is first on the hardware. Type 2 sits on top of a second layer, the host OS.
2.6Which Wi-Fi standard introduced OFDMA, and what does Wi-Fi 6E add?
802.11ax (Wi-Fi 6) introduced OFDMA for dense environments. Wi-Fi 6E extends it to the 6 GHz band.
Memory note: The 6 GHz band requires WPA3.
2.7Which 2.4 GHz Wi-Fi channels do not overlap in North America?
Channels 1, 6, and 11.
Memory note: Assign neighboring access points to different channels from this set to reduce interference.
2.8In IaaS, PaaS, and SaaS, who manages the operating system?
- IaaS: the customer manages the OS, runtime, and applications (for example, AWS EC2).
- PaaS: the provider manages the OS and runtime; the customer deploys code (for example, Heroku).
- SaaS: the provider manages everything; the customer manages settings and data (for example, Microsoft 365).
Memory note: Moving from IaaS to SaaS, the customer manages less at each step.
2.9Does an M.2 slot guarantee NVMe speeds?
No. M.2 is a physical form factor. A slot can support SATA, NVMe, or both, so check the motherboard manual before buying a drive.
2.10What are the main DC output voltages of a PC power supply?
3.3 V, 5 V, and 12 V. The motherboard uses a 20+4-pin main connector.
Memory note: The 12 V rail powers the most demanding components, such as the CPU and graphics card.
Deck 3 · Core 2: Command-line utilities and OS tools
Windows and Linux commands, and when to use each one.
3.1Which command repairs corrupted Windows system files?
sfc /scannow (System File Checker).
Memory note: If sfc cannot repair files, run DISM /Online /Cleanup-Image /RestoreHealth to fix the component store, then run sfc again. DISM is not named in the V15 objectives.
3.2Which Windows command reapplies Group Policy immediately?
gpupdate /force
Memory note: Use gpresult /r to confirm which Group Policy Objects were applied.
3.3What do the chkdsk /f and /r switches do?
- /f: fixes file system errors on the disk.
- /r: locates bad sectors and recovers readable data. It includes /f.
3.4Which Linux command changes file permissions, and what does 755 mean?
chmod. In 755:
- 7 for the owner: read + write + execute (4 + 2 + 1)
- 5 for the group: read + execute (4 + 1)
- 5 for others: read + execute (4 + 1)
Memory note: Read = 4, write = 2, execute = 1. Add them for each position.
3.5Which command shows active connections, listening ports, and the process IDs that own them?
netstat -ano
Memory note: -a shows all connections, -n shows numeric addresses, and -o adds the PID. Match the PID in Task Manager to find the program.
3.6A Windows client has a 169.254.x.x address. Which commands request a new address from DHCP?
ipconfig /release followed by ipconfig /renew.
Memory note: Use ipconfig /all to check the DHCP server, DNS servers, and lease details.
3.7What is the difference between tracert and pathping?
tracert lists each hop to a destination with its latency. pathping also measures packet loss at each hop over a period of time.
3.8Which Windows command maps a network share to a drive letter?
net use Z: \\server\share
3.9What is the difference between sudo and su in Linux?
sudo runs a single command with root privileges, using your own password and the permissions in the sudoers file. su switches to another user account, root by default, and requires that account's password.
3.10Which Windows tool should you check first for crash and startup error logs?
Event Viewer (eventvwr.msc). Review the System and Application logs.
Deck 4 · Core 2: Security and operational procedures
Malware removal, social engineering, authentication, safety, and policies.
4.1What are the seven steps of CompTIA's malware removal procedure, in order?
- Investigate and verify malware symptoms.
- Quarantine the infected system.
- Disable System Restore in Windows Home.
- Remediate: update anti-malware software, scan and remove (safe mode or a preinstallation environment), and reimage or reinstall if needed.
- Schedule scans and run updates.
- Enable System Restore and create a restore point in Windows Home.
- Educate the end user.
Memory note: Steps 3 and 6 mirror each other: disable System Restore, then enable it again. Updating definitions happens in step 4, not first.
4.2Which social engineering attack targets senior executives such as CEOs or CFOs?
Whaling, a form of spear phishing aimed at high-value targets.
Memory note: Phishing is a wide net, spear phishing is aimed at one target, and whaling goes after the biggest fish.
4.3What is the difference between phishing and pharming?
- Phishing: uses deceptive emails or messages to lure users to fake sites or to reveal information.
- Pharming: uses technical tampering, such as DNS poisoning or a modified hosts file, to redirect users silently, even when they type the correct address.
Memory note: Pharming is not named in the V15 objectives, but the hosts file and DNS settings are.
4.4What are the three main authentication factor categories used in MFA?
- Something you know: passwords, PINs, security questions.
- Something you have: smart cards, hardware tokens, authenticator apps.
- Something you are: biometrics such as fingerprints and facial recognition.
Memory note: Two passwords are still a single factor. MFA requires factors from different categories. Some references add somewhere you are (location) and something you do.
4.5What prevents electrostatic discharge (ESD) damage when working inside a PC?
An ESD wrist strap clipped to unpainted metal on the computer chassis, used with an ESD mat. Store components in antistatic bags.
Memory note: Disconnect the power cord before opening the case.
4.6What does WPA3 use instead of WPA2's pre-shared key handshake?
SAE (Simultaneous Authentication of Equals). It resists offline password-guessing attacks and provides forward secrecy.
4.7What is the 3-2-1 backup rule?
Keep 3 copies of data, on 2 different types of media, with 1 copy offsite.
Memory note: Test restores regularly. A backup that has never been restored is unproven.
4.8What is the difference between a surge suppressor and a UPS?
A surge suppressor protects against voltage spikes. A UPS supplies battery power during brownouts and blackouts so equipment can keep running or shut down safely, and most models also suppress surges.
4.9In AI tools, what is a hallucination?
A confident-sounding response that is false or fabricated. Verify AI output against trusted sources before acting on it.
Memory note: AI concepts are new in the V15 Core 2 objectives, along with bias, accuracy, data privacy, and appropriate-use policies.
4.10What does chain of custody document during an incident?
Who handled the evidence, when, and what was done with it, from collection onward, so its integrity can be proven.
Memory notes
Groupings and patterns that make the most-tested facts easier to recall.
Spot the look-alikes
- 443 vs. 445: 443 is the secure web; 445 is Windows shares.
- 22 vs. 23: the secure protocol (SSH) comes first; Telnet is one port later.
- 67 vs. 68: the DHCP server gets the lower number, and the client the higher.
- 110 vs. 143: POP3 pulls mail down; IMAP keeps it in sync.
Troubleshooting steps in order
Identify, Theory, Test, Plan, Verify, Document. Our mnemonic: "I Think Tech People Verify Details."
Back up data before making changes, and escalate at the test step if the problem is outside your scope.
Malware removal in order
Investigate, Quarantine, Disable System Restore, Remediate, Schedule scans and updates, Enable System Restore, Educate.
Disable comes before remediation, and Enable comes after, so infected restore points are never kept.
RAID at a glance
- Minimum drives: RAID 0 and 1 need 2; RAID 5 needs 3; RAID 6 and 10 need 4.
- Failures survived: RAID 0 none, RAID 5 one, RAID 6 two.
- Usable capacity: RAID 5 loses one drive to parity; RAID 6 loses two; RAID 1 and 10 keep half.
Linux permission math
Read = 4, Write = 2, Execute = 1. Add them for owner, group, and others.
755: rwx r-x r-x (typical for programs and directories)644: rw- r-- r-- (typical for regular files)700: rwx --- --- (private to the owner)
Continue the CompTIA A+ study path
Practice exams are still being prepared.
Overview
Exam format, scoring, domain weights, V15 changes, and exam strategy.
Core Notes
Technical reference notes for networking, hardware, cloud, operating systems, and security.
Flashcards & Memory Notes
40 recall cards in four decks, plus memory notes for the most-tested facts.
Practice Exams
Original practice questions with explanations and a clearly stated scope. No release date is promised.
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