A solid grasp of networking is fundamental for any cyber or infrastructure engineer. This page provides a quick reference to the most commonly used IP ports (including secure variants), a breakdown of TCP/UDP usage, and the key internal IP ranges — including the lesser-known APIPA.

🔌 Common IP Ports (with TCP/UDP and Protocol Reasoning)

🔒 Secure Versions of Common Ports

🧠 Database Ports Reference Guide

🗄️ Relational Database Ports (SQL)

📦 NoSQL & Search Engine Ports

☁️ Cloud SQL Service Ports (Typically Encapsulated)

🔐 Note: Cloud SQL services often use TLS by default and restrict access using IAM, firewalls, or client certificates rather than exposing raw database ports publicly.

🏠 Internal IP Address Ranges (RFC1918 & APIPA)

These IP ranges are not routable on the public internet and are used for internal networking:

🔹 Private IP Ranges

10.0.0.0 – 10.255.255.255       (Class A, /8)
172.16.0.0 – 172.31.255.255     (Class B, /12)
192.168.0.0 – 192.168.255.255   (Class C, /16)

These are often used in home networks, enterprise LANs, and VPNs. NAT (Network Address Translation) allows these private IPs to communicate externally.

🔹 APIPA (Automatic Private IP Addressing)

169.254.0.0 – 169.254.255.255

If a device cannot contact a DHCP server and has APIPA enabled, it assigns itself an IP in this range. This allows basic communication between devices on the same subnet but does not allow internet access.

🧭 Why This Matters

Understanding ports and addressing is critical for:

• Configuring firewalls and ACLs
• Diagnosing connectivity issues
• Monitoring network traffic for threats
• Securing services by enforcing encrypted communication

🔥 Top Exploited Ports (Attack Surface Awareness)

Ports commonly targeted by attackers:

🛡️ Hardening Tips

Include basic best practices for port/service security:

• Close unused ports.
• Use firewalls to restrict external access.
• Prefer secure alternatives (SSH over Telnet, HTTPS over HTTP).
• Monitor open ports with tools like nmap, netstat, or ss.
• Use port knocking or VPNs for sensitive services like SSH and RDP.
• Enforce 2FA where possible for remote access services.

🧰 Troubleshooting & Discovery Tools

Quick CLI examples to discover or check open ports:

# Discover open ports on a target
nmap -sS -Pn 192.168.0.10

# List listening ports on a Linux host
ss -tuln

# Find which process is using a port
lsof -i :3306

# Discover open ports on a target
nmap -sS -Pn 192.168.0.10

# List listening ports on a Linux host
ss -tuln

# Find which process is using a port
lsof -i :3306

🧱 OSI Model with Protocol Examples