Reference Sheet
Common Ports & Protocols
A+ Exam · Networking fundamentals
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File Transfer & Remote Access
| Port | Protocol | Service | Purpose | Memory Hook |
|---|---|---|---|---|
| 20-21 | TCP | FTP — File Transfer Protocol | Transfers files between a client and server; 20 moves data, 21 handles commands. | 21 is the boss — commands and control; 20 does the work |
| 22 | TCP | SSH — Secure Shell | Encrypted remote command-line access to a device. | "22 = two locks" — Secure Shell, everything encrypted |
| 23 | TCP | Telnet | Unencrypted remote command-line access — insecure, largely replaced by SSH. | 23 = old, plaintext, insecure — replaced by SSH (22) |
| 3389 | TCP | RDP — Remote Desktop Protocol | Remote graphical desktop access to a Windows computer. | "33-89 = Remote Desktop" — Windows remote GUI access |
| Port | Protocol | Service | Purpose | Memory Hook |
|---|---|---|---|---|
| 25 | TCP | SMTP — Simple Mail Transfer Protocol | Sends outbound email from a client to a server, or between mail servers. | "Send Mail To People" — 25 letters in the alphabet (minus 1) |
| 110 | TCP | POP3 — Post Office Protocol 3 | Downloads email to a single device, typically removing it from the server. | POP3 = 110; "Point Of Pickup" — grabs mail and removes it from server |
| 143 | TCP | IMAP — Internet Mail Access Protocol | Synchronizes email across multiple devices; messages stay on the server. | "I MAP 143" — syncs across devices, mail lives on server |
Web
| Port | Protocol | Service | Purpose | Memory Hook |
|---|---|---|---|---|
| 80 | TCP | HTTP — Hypertext Transfer Protocol | Transfers unencrypted web page content between browser and server. | "80 = HTTP" — standard web, no padlock |
| 443 | TCP/UDP | HTTPS — HTTP Secure | Transfers encrypted web page content between browser and server (HTTP over TLS). | "443 = padlock" — HTTPS, the secure web |
Network Services
| Port | Protocol | Service | Purpose | Memory Hook |
|---|---|---|---|---|
| 53 | TCP/UDP | DNS — Domain Name System | Resolves domain names to IP addresses. | "53 = DNS" — UDP for queries, TCP for zone transfers |
| 67-68 | UDP | DHCP — Dynamic Host Configuration Protocol | Automatically assigns IP addresses and network settings to clients; 67 = server, 68 = client. | 67 server, 68 client — one apart, always together |
File Sharing & Directory Services
| Port | Protocol | Service | Purpose | Memory Hook |
|---|---|---|---|---|
| 137-139 | TCP/UDP | NetBIOS / NetBT | Legacy name resolution and session services for Windows file/print sharing over TCP/IP. | 137-139 = old-school Windows networking, pre-dates SMB direct-hosting on 445 |
| 389 | TCP/UDP | LDAP — Lightweight Directory Access Protocol | Queries and authenticates against a directory service, e.g. Active Directory. | "389 = LDAP" — 3-8-9 = find the user |
| 445 | TCP | SMB / CIFS — Server Message Block / Common Internet File System | Shares files and printers on a Windows network. | "445 = Samba" — Windows networking; 4 + 4 + 5 = shared drives |