Think: apartment building
The IP address gets traffic to the correct building/device. The port number helps deliver it to the correct apartment/service on that device.
A+ networking study lab
Ports, Protocols & Memory Tricks
A port number helps a computer direct network traffic to the correct service. Do not memorize a number by itself—connect the port + protocol + purpose + security clue.
A+ quick links
A+ Home
Mission 01
Mission 02
Mission 03
Test Readiness
Ports
OSI / TCP-IP
Practice
A+ Terms
Notebook
First, understand the idea
IP address = which device. Port = which service.
TCP vs. UDP
TCP emphasizes reliable, ordered delivery with a connection. UDP has less connection overhead and is useful where speed/low latency or simple request-response behavior matters. A protocol may use TCP, UDP, or both.
Exam habit: Ask, “What is the scenario trying to do?” Secure website → HTTPS → 443. Resolve a name → DNS → 53. Automatically receive IPv4 settings → DHCP → 67/68. Remote Windows desktop → RDP → 3389.
| Port | Service | Transport | What it does | Memory hook |
|---|---|---|---|---|
| 20 | FTP data | TCP | File Transfer Protocol data channel (traditional active FTP). | 20 = the data suitcase; 21 = the control desk. |
| 21 | FTP control | TCP | FTP commands/control connection. | FTP lives in the 20s: 20 data, 21 control. |
| 22 | SSH / SFTP | TCP | Secure remote shell; SFTP transfers files through SSH. | 22 = two secure shoes: SSH walks in securely. |
| 23 | Telnet | TCP | Legacy unencrypted remote terminal. | 23 follows secure 22, but Telnet is the unsafe neighbor. |
| 25 | SMTP | TCP | Mail transfer between mail systems; submission commonly uses other ports too. | 25 = SMTP sends mail out. |
| 53 | DNS | UDP/TCP | Name-to-IP resolution; commonly UDP, with TCP also used for some DNS operations. | DNS has 53 letters? No—memorize: 'DNS = 53' as a fixed pair. |
| 67 | DHCP server | UDP | Server side of automatic IPv4 address configuration. | Server serves first: 67. |
| 68 | DHCP client | UDP | Client side of automatic IPv4 address configuration. | Client receives next: 68. |
| 80 | HTTP | TCP | Unencrypted web traffic. | 80 = ordinary web. |
| 110 | POP3 | TCP | Downloads/retrieves email from a mailbox. | POP = 110. |
| 123 | NTP | UDP | Synchronizes time across networked systems. | 1-2-3 = time/counting = NTP. |
| 143 | IMAP | TCP | Accesses and synchronizes email while keeping mail on the server. | IMAP = 143. |
| 161 | SNMP queries | UDP | Network monitoring/management queries. | 161 asks; 162 alerts. |
| 162 | SNMP traps | UDP | SNMP notifications/traps sent to a manager. | 161 asks; 162 alerts. |
| 389 | LDAP | TCP/UDP | Directory service queries, commonly associated with directory authentication environments. | LDAP = 389. |
| 443 | HTTPS | TCP | Encrypted web traffic using TLS. | 443 = secure web; think 'locked 443'. |
| 445 | SMB | TCP | Windows-style file/printer sharing and related network services. | 445 = sharing files. |
| 3389 | RDP | TCP/UDP | Remote Desktop Protocol. | 3389 = the big remote-desktop number. |
Chunk, don't cram
Memorize in families.
20 / 21 / 22 / 23 / 25
The early service neighborhood
FTP data 20 → FTP control 21 → secure remote SSH 22 → insecure remote Telnet 23 → mail transfer SMTP 25.
53 → 67/68 → 80
Get online
DNS finds the address (53), DHCP gives network settings (67/68), HTTP opens the ordinary web (80).
110 / 143
Mailbox pair
POP3 = 110. IMAP = 143. Remember both as email retrieval/access protocols, then learn how their behavior differs.
161 / 162
SNMP pair
161 asks for management information; 162 alerts with traps/notifications.
80 → 443
Web pair
HTTP 80 is ordinary web traffic. HTTPS 443 adds TLS encryption. On an exam, “secure website” should immediately suggest 443.
445 / 3389
Windows environment clues
SMB 445 → shared files/printers. RDP 3389 → remote desktop.
Do not trust the memory trick more than the concept. The trick gets you to the number; understanding the service gets you through scenario questions.
Notebook
Build a port-number foldable or two-column recall page.
Front / left side
Write only the number: 22, 53, 80, 443, 3389… Try to recall the service before opening the flap or looking right.
Back / right side
Add name → TCP/UDP → purpose → secure/insecure clue → memory hook. Star the ports you repeatedly miss instead of rewriting every definition.