Common Ports & Protocols
Key Takeaways
- Port numbers range from 0 to 65,535 and are divided into well-known (0-1023), registered (1024-49151), and dynamic/ephemeral (49152-65535) ranges.
- You must memorize key port numbers for the exam: HTTP (80), HTTPS (443), FTP (20/21), SSH (22), Telnet (23), SMTP (25), DNS (53), DHCP (67/68), POP3 (110), IMAP (143), RDP (3389), and SMB (445).
- Secure versions of protocols typically use different ports: HTTPS uses 443 instead of 80, SFTP uses 22, IMAPS uses 993, POP3S uses 995, and SMTPS uses 465 or 587.
- DNS translates domain names to IP addresses and is essential for all internet browsing — DNS failure makes it appear as if the internet is down even when connectivity exists.
- DHCP automatically assigns IP addresses, subnet masks, default gateways, and DNS server addresses to network devices, eliminating the need for manual configuration.
Last updated: March 2026
Common Ports & Protocols
Port Number Ranges
| Range | Category | Description |
|---|---|---|
| 0–1,023 | Well-Known Ports | Reserved for standard services (HTTP, FTP, DNS, etc.) |
| 1,024–49,151 | Registered Ports | Assigned to specific applications (RDP, SQL, etc.) |
| 49,152–65,535 | Dynamic/Ephemeral | Temporarily assigned for client-side connections |
Essential Ports to Memorize
Web & File Transfer
| Port | Protocol | Description | TCP/UDP |
|---|---|---|---|
| 20 | FTP Data | File Transfer Protocol — data channel | TCP |
| 21 | FTP Control | File Transfer Protocol — command channel | TCP |
| 22 | SSH/SFTP/SCP | Secure Shell, Secure FTP, Secure Copy | TCP |
| 23 | Telnet | Unsecured remote terminal access | TCP |
| 80 | HTTP | Hypertext Transfer Protocol (unencrypted web) | TCP |
| 443 | HTTPS | HTTP Secure (encrypted with TLS) | TCP |
| Port | Protocol | Description | TCP/UDP |
|---|---|---|---|
| 25 | SMTP | Simple Mail Transfer Protocol (sending email) | TCP |
| 110 | POP3 | Post Office Protocol v3 (receiving email) | TCP |
| 143 | IMAP | Internet Message Access Protocol (receiving email) | TCP |
| 465 | SMTPS | SMTP over SSL (legacy secure sending) | TCP |
| 587 | SMTP (STARTTLS) | SMTP with STARTTLS encryption (modern secure sending) | TCP |
| 993 | IMAPS | IMAP over SSL/TLS (secure receiving) | TCP |
| 995 | POP3S | POP3 over SSL/TLS (secure receiving) | TCP |
Network Services
| Port | Protocol | Description | TCP/UDP |
|---|---|---|---|
| 53 | DNS | Domain Name System (name resolution) | TCP & UDP |
| 67 | DHCP Server | Dynamic Host Configuration Protocol (server) | UDP |
| 68 | DHCP Client | Dynamic Host Configuration Protocol (client) | UDP |
| 69 | TFTP | Trivial File Transfer Protocol (simple, no auth) | UDP |
| 161 | SNMP | Simple Network Management Protocol (monitoring) | UDP |
| 162 | SNMP Trap | SNMP alerts/notifications | UDP |
| 389 | LDAP | Lightweight Directory Access Protocol | TCP |
| 636 | LDAPS | LDAP over SSL/TLS (secure) | TCP |
Remote Access & File Sharing
| Port | Protocol | Description | TCP/UDP |
|---|---|---|---|
| 445 | SMB/CIFS | Server Message Block (Windows file sharing) | TCP |
| 3389 | RDP | Remote Desktop Protocol (Windows remote access) | TCP |
| 5900 | VNC | Virtual Network Computing (remote desktop) | TCP |
Key Protocol Details
DNS (Domain Name System) — Port 53
DNS translates human-readable domain names (www.example.com) into IP addresses (93.184.216.34):
| Record Type | Purpose | Example |
|---|---|---|
| A | Maps hostname to IPv4 address | example.com → 93.184.216.34 |
| AAAA | Maps hostname to IPv6 address | example.com → 2606:2800:220:1:... |
| MX | Mail exchanger for the domain | example.com → mail.example.com |
| CNAME | Alias for another domain name | www.example.com → example.com |
| TXT | Text records (SPF, DKIM, verification) | example.com → "v=spf1 ..." |
| NS | Authoritative name servers | example.com → ns1.example.com |
| PTR | Reverse DNS (IP to hostname) | 93.184.216.34 → example.com |
DHCP (Dynamic Host Configuration Protocol) — Ports 67/68
DHCP automatically assigns network configuration to devices using the DORA process:
- Discover — Client broadcasts "I need an IP address" (UDP 67)
- Offer — DHCP server responds with an available IP address offer
- Request — Client requests the offered IP address
- Acknowledge — Server confirms and assigns the IP address
DHCP assigns:
- IP address
- Subnet mask
- Default gateway
- DNS server addresses
- Lease duration (how long the assignment is valid)
FTP (File Transfer Protocol) — Ports 20/21
FTP uses two separate connections:
- Port 21 — Control channel (commands, authentication)
- Port 20 — Data channel (actual file transfers)
FTP Modes:
- Active Mode: Server initiates data connection back to client (may be blocked by client firewalls)
- Passive Mode: Client initiates both connections (firewall-friendly)
Security Note: FTP transmits credentials in plaintext. Use SFTP (port 22) or FTPS (port 990) for encrypted file transfer.
Test Your Knowledge
Which port number is used by HTTPS?
A
B
C
D
Test Your Knowledge
What does the DHCP "DORA" process stand for?
A
B
C
D
Test Your KnowledgeMatching
Match each port number to its protocol:
Match each item on the left with the correct item on the right
1
Port 22
2
Port 53
3
Port 3389
4
Port 445
Test Your Knowledge
A DNS record that maps a domain name to an IPv4 address is called:
A
B
C
D