Home > Networking Fundamentals > Common Port Numbers
Common Port Numbers for the CompTIA A+ Exam
Port numbers are one of the most tested networking topics on the CompTIA A+ exam.
You don’t need to memorize every port — but you MUST know the common ones.
What Is a Port Number?
A port number is a logical communication endpoint used by network services.
Think of an IP address as an apartment building, and the port number as the apartment number.
IP address = the building
Port number = the specific service inside the building
Most Important A+ Port Numbers
| Port |
Protocol |
Service |
| 20 / 21 |
TCP |
FTP (File Transfer Protocol) |
| 22 |
TCP |
SSH (Secure Shell) |
| 23 |
TCP |
Telnet |
| 25 |
TCP |
SMTP (Email Sending) |
| 53 |
UDP / TCP |
DNS |
| 80 |
TCP |
HTTP |
| 110 |
TCP |
POP3 |
| 143 |
TCP |
IMAP |
| 443 |
TCP |
HTTPS |
| 3389 |
TCP |
RDP (Remote Desktop) |
Memory Tricks
- 80 → Web (HTTP)
- 443 → Secure Web (HTTPS)
- 22 → SSH (two 2’s = secure)
- 3389 → Remote Desktop
- 53 → DNS (short number = fast lookup)
If you see a question mentioning secure web traffic, think: Port 443.
Why Port Numbers Matter on the A+ Exam
You may see questions like:
- “A user cannot access a website using HTTPS. Which port should be checked?”
- “Which port does RDP use?”
- “Which protocol uses port 53?”
These are straightforward points if you memorize the common ports.
Troubleshooting Example
A user can access HTTP websites but not HTTPS websites.
What should you check?
Check if port 443 is blocked by the firewall.
Related Networking Articles
Recommended A+ Study Tools
Lock in these port numbers with practice exams and structured review:
Final Summary
- Port numbers identify specific services
- HTTP = 80
- HTTPS = 443
- DNS = 53
- RDP = 3389
- These are high-yield exam topics