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. 3389Correct 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. 587Correct 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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