Question 1

What are network ports and why do they matter?

Accepted Answer

Network ports are logical endpoints in TCP/IP networking, numbered 0-65535, that enable multiple services to operate on a single IP address. Ports direct traffic to specific applications: web servers use 80/443, email uses 25/587/993, SSH uses 22. Understanding ports is essential for firewall configuration, troubleshooting connectivity, and securing network services properly.

Question 2

What is the difference between TCP and UDP ports?

Accepted Answer

TCP (Transmission Control Protocol) provides reliable, connection-oriented communication with error checking and guaranteed delivery. UDP (User Datagram Protocol) offers connectionless, faster communication without delivery guarantees. TCP suits applications needing reliability (HTTP, SSH, email); UDP suits speed-critical services (DNS, streaming, gaming). Many services support both protocols on the same port.

Question 3

What are well-known ports vs registered ports?

Accepted Answer

Well-known ports (0-1023) are reserved for common services by IANA and require administrator privileges. Examples: 22 (SSH), 80 (HTTP), 443 (HTTPS). Registered ports (1024-49151) are assigned to specific applications by IANA but don't require privileges. Dynamic/private ports (49152-65535) are temporary ports for client connections. Always verify port assignments before deployment.

Question 4

Which ports should I block on my firewall?

Accepted Answer

Block inbound connections on all ports except those explicitly required for services. High-risk ports include: 23 (Telnet), 135-139/445 (SMB/NetBIOS), 3389 (RDP), 5900 (VNC). Allow only: 80/443 for web, 22 for SSH (change default), required application ports. Implement egress filtering too, blocking unexpected outbound connections to prevent data exfiltration and command-and-control communication.

Question 5

What are common ports used by attackers?

Accepted Answer

Attackers frequently target: 22 (SSH brute force), 23 (Telnet default credentials), 80/443 (web vulnerabilities), 3389 (RDP attacks), 445 (SMB exploits like WannaCry), 21 (FTP), 1433/3306 (databases). They also scan high ports for backdoors and use non-standard ports to evade detection. Monitor all open ports, not just common targets, with intrusion detection systems.

Question 6

How do I find what ports are open on my system?

Accepted Answer

Windows: Run "netstat -ano" or "Get-NetTCPConnection" in PowerShell. Linux/Mac: Run "netstat -tuln", "ss -tuln", or "lsof -i". External scanning: Use nmap ("nmap -sT [IP]") or online port scanners. Always scan from both internal and external perspectives to understand exposure. Document all open ports and their purposes for security baseline and compliance.

Question 7

Should I change default ports for security?

Accepted Answer

Changing default ports provides minimal security through obscurity. It reduces automated scanning but determined attackers will discover services regardless. Better strategies: disable unnecessary services, use strong authentication, keep software updated, implement network segmentation, and monitor traffic. If changing ports, document changes carefully and ensure monitoring tools reflect new configurations to avoid blind spots.

Question 8

What is port forwarding and when should I use it?

Accepted Answer

Port forwarding redirects external traffic to internal network devices, enabling services like remote desktop, web servers, or game servers behind NAT. Configure on routers to map external ports to internal IP:port combinations. Use cautiously: each forwarded port increases attack surface. Prefer VPN access over port forwarding. If necessary, use non-standard ports, strong authentication, and monitor logs regularly.

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