👈

• 🚪 What is a Port?
  • 📦 Why Ports are Needed
  • 🔢 Port Range (Very Important)
    • Categories:
    • 1️⃣ Well-Known Ports (0–1023)
    • 2️⃣ Registered Ports (1024–49151)
    • 3️⃣ Dynamic / Ephemeral Ports (49152–65535)
  • ⭐ Common Ports You MUST Remember (AWS + Interviews)
  • 🧠 How Ports Work (Simple Flow)
  • 🔐 TCP vs UDP Ports
    • 🧱 TCP (Reliable)
    • ⚡ UDP (Fast)
  • ☁️ Ports in AWS (Very Important)
    • Security Group = Firewall
  • 🧪 Real AWS Example
  • 🛑 Important AWS Exam Traps
  • 🔍 Check Open Ports (Linux)
    • Check listening ports:
  • 🧠 One-Line Exam Definition
  • 📝 Quick Memory Trick

🚪 What is a Port?

A port is like a door on a computer or server.

• IP address → identifies the machine
• Port number → identifies the application/service on that machine

👉 IP = building address 👉 Port = flat/room number

📦 Why Ports are Needed

One server runs many services at the same time:

Without ports: ❌ Computer wouldn’t know which service should receive the data.

🔢 Port Range (Very Important)

Ports range from:

0 – 65535

Categories:

1️⃣ Well-Known Ports (0–1023)

Reserved for common services.

2️⃣ Registered Ports (1024–49151)

Used by applications.

3️⃣ Dynamic / Ephemeral Ports (49152–65535)

Temporary ports used by clients.

⭐ Common Ports You MUST Remember (AWS + Interviews)

🧠 How Ports Work (Simple Flow)

Example: You open a website.

1️⃣ Your browser uses a random client port

Example: 52344

2️⃣ It connects to server:

Server IP : 443

3️⃣ Server replies back to:

Your IP : 52344

✔ Server port is fixed ✔ Client port is temporary

🔐 TCP vs UDP Ports

Ports work with protocols.

🧱 TCP (Reliable)

• Connection-oriented
• Slower but safe

Used for:

• HTTP (80)
• HTTPS (443)
• SSH (22)

⚡ UDP (Fast)

• No connection
• Faster but not guaranteed

Used for:

• DNS (53)
• Video streaming
• Gaming

☁️ Ports in AWS (Very Important)

Security Group = Firewall

Security Groups control:

• Which ports are allowed
• From which IP

Example:

Allow inbound:
Port 22 → My IP
Port 80 → 0.0.0.0/0

If port is closed: ❌ Service is running ❌ But cannot be accessed

🧪 Real AWS Example

You launch EC2 and install Apache.

Apache listens on:

Port 80

But you forget to open port 80 in Security Group.

Result: ❌ Website not accessible

👉 Security Group must allow the port

🛑 Important AWS Exam Traps

❗ EC2 not accessible? Check:

1. Security Group
2. NACL
3. Correct port
4. Correct protocol (TCP/UDP)

🔍 Check Open Ports (Linux)

Check listening ports:

ss -tuln

or

netstat -tuln

🧠 One-Line Exam Definition

A port is a logical communication endpoint that allows multiple services to run on the same IP address.

📝 Quick Memory Trick

• 22 → SSH
• 80 → Web
• 443 → Secure Web
• 3306 → MySQL
• 5432 → PostgreSQL