CompTIA A+ Port Numbers: The Complete Quick-Reference Cheat Sheet (Core 1 220-1101)

Moznu — Mon, 05 Oct 2026 04:47:15 +0000

Every candidate sitting for the CompTIA A+ Core 1 (220-1101) exam encounters port questions—either directly ("Which port does LDAPS operate on?") or embedded inside performance-based firewall troubleshooting questions.

Knowing your ports by heart is free points on test day. Here is the authoritative breakdown of every required port, categorized by service type, along with memory hooks to lock them in.

1. Quick-Reference Master Table

Port	Protocol / Service	Transport	Description	Secure Alternative
20/21	FTP (File Transfer Protocol)	TCP	Unencrypted file transfer (20: Data, 21: Control)	SFTP (Port 22) / FTPS (Port 990/989)
22	SSH (Secure Shell) / SFTP	TCP	Encrypted terminal access & secure file transfer	N/A (Standard secure protocol)
23	Telnet	TCP	Unencrypted remote command-line terminal	SSH (Port 22)
25	SMTP (Simple Mail Transfer)	TCP	Sending outbound mail between mail servers	SMTPS (Port 465 or 587)
53	DNS (Domain Name System)	UDP/TCP	Resolves FQDN hostnames to IP addresses	DNS over HTTPS (Port 443)
67/68	DHCP (Dynamic Host Config)	UDP	Assigns dynamic IP configurations (67: Server, 68: Client)	N/A
69	TFTP (Trivial FTP)	UDP	Lightweight, connectionless file transfer (PXE booting)	SFTP / SCP
80	HTTP (HyperText Transfer)	TCP	Unencrypted web traffic	HTTPS (Port 443)
110	POP3 (Post Office Protocol 3)	TCP	Downloads mail to a local client and deletes from server	POP3S (Port 995)
123	NTP (Network Time Protocol)	UDP	Synchronizes clock time across network hosts	N/A
137-139	NetBIOS	UDP/TCP	Legacy Windows LAN name resolution & file sharing	Direct SMB (Port 445)
143	IMAP (Internet Message Access)	TCP	Synchronizes mail folders across multiple clients	IMAPS (Port 993)
161/162	SNMP (Simple Network Mgmt)	UDP	Network monitoring & device traps (161: Queries, 162: Traps)	SNMPv3 (encrypted)
389	LDAP (Lightweight Directory Access)	TCP/UDP	Queries Active Directory / directory services	LDAPS (Port 636)
443	HTTPS (HTTP Secure)	TCP	TLS/SSL encrypted web traffic	N/A (Gold standard)
445	SMB (Server Message Block)	TCP	Modern Windows network file & print sharing	N/A
636	LDAPS (LDAP Secure)	TCP	TLS-encrypted Active Directory queries	N/A
3389	RDP (Remote Desktop Protocol)	TCP/UDP	Microsoft graphical remote desktop session	N/A

2. Web & Mail Protocols: The Insecure vs. Secure Pairs

CompTIA loves asking which secure protocol replaces an obsolete legacy protocol in a hardened environment:

Web Traffic

HTTP (80) ➔ Replaced by HTTPS (443). Uses TLS to encrypt session data.

Email Protocols

Outbound Sending:
- Unencrypted: SMTP (Port 25)
- Secure Submission: Port 587 (STARTTLS) or Port 465 (SMTPS).
Inbound Retrieval:
- POP3: Insecure on Port 110, Secure on Port 995. Downloads and stores locally.
- IMAP: Insecure on Port 143, Secure on Port 993. Keeps mail on the server and synchronizes across phone/laptop.

3. Remote Management: Telnet vs. SSH vs. RDP

Telnet (Port 23): Transmits commands and passwords in plaintext. Never use over an untrusted network.
SSH (Port 22): Uses public-key cryptography to provide an encrypted CLI session. Also powers SFTP.
RDP (Port 3389): Microsoft's graphical remote desktop connection tool.

4. 4 Memory Hooks for Exam Day

"DNS = Half a Dollar + 3": DNS is Port 53. (Also remember it uses UDP for standard queries and TCP for large zone transfers).
"SSH is 22, Telnet is 23": Telnet is one step after SSH, but SSH is encrypted while Telnet is exposed.
"RDP has 4 digits: 3-3-8-9": Remind yourself of the 3389 cadence—3, 3, then (8, 9).
"POP3S (995) & IMAPS (993)": Notice how both secure mail retrieval ports are in the 990s.

5. Sample CompTIA Practice Questions

Question 1:

A network administrator needs to securely query an Active Directory server across an external branch link. Which port must be opened on the edge firewall?

A. 389

B. 445

C. 636

D. 3389

Correct Answer: C (Port 636 - LDAPS)

Explanation: Standard LDAP operates on port 389 in cleartext. Over an untrusted link, secure LDAP over TLS (LDAPS) running on port 636 is strictly required.

Question 2:

A technician setting up a local mail server notices outgoing client mail is blocked by the upstream ISP on port 25. Which alternative port should the clients configure for authenticated submission?

A. 110

B. 143

C. 443

D. 587

Correct Answer: D (Port 587)

Explanation: ISPs frequently block port 25 to prevent spam bots. Modern email clients submit outbound messages via SMTP submission on port 587 using TLS.

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DEV Community: Moznu