The Ultimate Guide to the Top 20 Common Network Ports and Their Functions

Introduction

Understanding network ports is fundamental in cybersecurity and IT. Ports act as communication gateways, enabling data exchange between devices and services. Attackers frequently target open or misconfigured ports, making port knowledge essential for defenders and penetration testers alike. This guide explores key ports, their functions, and security implications.

Learning Objectives

• Identify the most commonly used network ports and their purposes.
• Learn how to secure critical ports against exploitation.
• Understand the role of ports in network communication and attacks.

1. Port 20/21 (TCP) – FTP (File Transfer Protocol)

Command:

ftp <IP_ADDRESS> 

What It Does:

FTP transfers files between systems. Port 20 handles data transfer, while Port 21 manages control signals.

Security Risk:

• Transmits credentials in plaintext.
• Use SFTP (Port 22) or FTPS (Port 990) instead.
  1. Port 22 (TCP) – SSH (Secure Shell)

Command:

ssh username@<IP_ADDRESS> 

What It Does:

SSH provides encrypted remote access to systems, replacing insecure protocols like Telnet.

Security Tip:

• Disable root login and enforce key-based authentication:

  sudo nano /etc/ssh/sshd_config 
  Set: PermitRootLogin no 
  Set: PasswordAuthentication no 
  

  1. Port 53 (UDP/TCP) – DNS (Domain Name System)

Command:

nslookup example.com 

What It Does:

DNS translates domain names (e.g., google.com) to IP addresses.

Security Risk:

• DNS poisoning and spoofing attacks.
• Use DNSSEC for validation.
  1. Port 80 (TCP) – HTTP (Hypertext Transfer Protocol)

Command:

curl http://example.com 

What It Does:

HTTP facilitates unencrypted web traffic.

Security Risk:

• Data interception.
• Always enforce HTTPS (Port 443).
  1. Port 443 (TCP) – HTTPS (HTTP Secure)

Command:

openssl s_client -connect example.com:443 

What It Does:

HTTPS encrypts web traffic using TLS/SSL.

Security Tip:

• Check certificate validity:

  openssl x509 -noout -text -in certificate.crt 
  

  1. Port 445 (TCP) – SMB (Server Message Block)

Command (Windows):

net use \<IP_ADDRESS>\<SHARE> 

What It Does:

SMB enables file sharing in Windows networks.

Security Risk:

• Exploited by ransomware (e.g., WannaCry).
• Disable SMBv1 and enforce SMB signing.
  1. Port 3389 (TCP) – RDP (Remote Desktop Protocol)

Command (Windows):

mstsc /v:<IP_ADDRESS> 

What It Does:

RDP allows remote GUI access to Windows systems.

Security Tip:

• Restrict RDP access via firewall rules.
• Use VPNs or RD Gateway for secure remote access.

What Undercode Say

• Key Takeaway 1: Misconfigured ports are low-hanging fruit for attackers—always disable unused services.
• Key Takeaway 2: Encryption (SSH, HTTPS) is non-negotiable for secure communications.

Analysis:

Network security hinges on port management. Attackers scan for open ports (e.g., 445, 3389) to exploit weak configurations. Defenders must adopt a zero-trust approach, regularly auditing ports and enforcing least-privilege access. As cloud adoption grows, securing API endpoints (often on Ports 80/443) becomes equally critical. Future threats will likely target IoT devices with exposed ports, making continuous monitoring essential.

Proactive Measures:

• Use `nmap` for port scanning:

  nmap -sV <IP_ADDRESS> 
  

• Implement IDS/IPS to detect port-based attacks.

By mastering port functions and hardening configurations, security teams can drastically reduce attack surfaces.

🔗 Enhance Your Skills: Ethical Hackers Academy (Use code LEARNCYBER for $100 off).

Final Thought:

“A closed port is a safe port—unless it’s supposed to be open, in which case, guard it fiercely.”

IT/Security Reporter URL:

Reported By: Kaaviya Balaji – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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