Top 20 Common Network Ports and Their Functions | Complete Guide for Beginners

Table of Contents

• What Is a Network Port?
• Top 20 Network Ports, Protocols, and Uses
• Why Are Network Ports Important?
•  Deep Dive into Key Ports
•  Real-World Example
• Security Tip: Monitor and Limit Open Ports
• Conclusion
•  Frequently Asked Questions (FAQs)

Understanding network ports is essential for anyone involved in cybersecurity, networking, IT support, or ethical hacking. Every time you browse a website, send an email, or connect to a remote server, you're using specific network ports. These ports help identify services on devices, ensuring data is delivered to the correct application.

In this blog, we’ll explain the top 20 most commonly used network ports, what they do, and why they’re important for security and network operations.

What Is a Network Port?

A network port is a virtual point where network connections start and end. When devices communicate, data travels through ports, identified by port numbers ranging from 0 to 65535. Each port is associated with a specific service, like HTTP, FTP, SSH, etc.

 Top 20 Network Ports, Protocols, and Uses

Why Are Network Ports Important?

• Security Monitoring: Intrusion detection systems monitor these ports for unauthorized activity.

• Firewall Configuration: Firewalls allow/block traffic based on port numbers.

• Troubleshooting: Understanding open/closed ports helps diagnose network issues.

• Attack Surface Awareness: Ports expose services that could be exploited if not properly secured.

Deep Dive into Key Ports

Port 22 (SSH)

Used to securely access remote servers using encryption. Widely used in system administration.

Port 80 (HTTP) and 443 (HTTPS)

These power most web applications. Port 443 encrypts traffic, making it secure for banking and login sites.

Port 21 & 20 (FTP)

Used for file transfers. Not secure by default, often replaced with SFTP or SCP.

Port 53 (DNS)

Resolves domain names like google.com to IP addresses. Crucial for internet functionality.

Port 445 (SMB)

Supports file and printer sharing in Windows environments. Often targeted in ransomware attacks.

Real-World Example

Let’s say you open a browser and go to http://example.com:

• Your computer sends a request to port 80 of the example.com server using the HTTP protocol.

• If it’s https, it uses port 443.

• If you connect to a server using Remote Desktop, it uses port 3389.

• When syncing your system clock, it talks to port 123 (NTP) servers.

Security Tip: Monitor and Limit Open Ports

Unnecessary open ports can become entry points for attackers. Always:

• Close unused ports

• Use a firewall to control port access

• Regularly scan your network with tools like Nmap, Wireshark, or Netcat

✅ Conclusion

Learning about network ports is a foundational skill in network administration and cybersecurity. Knowing which ports are open, why they're used, and how to secure them can protect systems from a wide range of attacks.

Whether you're a network engineer, ethical hacker, or just curious about how the internet works, this knowledge helps you understand the backbone of digital communication.

FAQs 

What is a network port in computer networking?

A network port is a communication endpoint used to identify specific processes or services on a device for data transmission.

How many network ports exist?

There are 65,535 ports available, divided into well-known (0–1023), registered (1024–49151), and dynamic/private (49152–65535) ranges.

What is the purpose of port 80?

Port 80 is used by the HTTP protocol for unencrypted web browsing over the internet.

What is port 443 used for?

Port 443 is used for HTTPS, which enables secure encrypted communication over the web.

What is the difference between TCP and UDP?

TCP is a connection-oriented protocol ensuring reliable data transfer, while UDP is faster but connectionless and does not guarantee delivery.

Why is port 22 important?

Port 22 is used for SSH (Secure Shell), allowing encrypted remote access to servers and systems.

Which port is used for DNS?

Port 53 is used by DNS (Domain Name System) for resolving domain names into IP addresses.

What is port 110 used for?

Port 110 is used for receiving emails using the POP3 protocol.

What port does FTP use?

FTP uses port 21 for control commands and port 20 for data transfer.

Is port 23 still used?

Port 23 is used for Telnet, but it's mostly obsolete and insecure due to lack of encryption.

What is port 25 used for?

Port 25 is commonly used for sending email using the SMTP protocol.

What port does RDP use?

RDP (Remote Desktop Protocol) uses port 3389 for remote access to Windows machines.

What is the function of port 143?

Port 143 is used by the IMAP protocol for receiving emails with server-side storage and synchronization.

What port does DHCP use?

DHCP uses port 67 (server to client) and port 68 (client to server) for assigning IP addresses dynamically.

Why is port 445 considered risky?

Port 445 supports SMB for file sharing in Windows, often exploited by ransomware like WannaCry.

What is port 69 used for?

Port 69 is used by TFTP (Trivial File Transfer Protocol) for basic file transfer operations.

What service runs on port 123?

Port 123 is used by NTP (Network Time Protocol) to synchronize clocks across systems.

What port is used by SNMP?

SNMP (Simple Network Management Protocol) typically runs on port 161 for network device management.

What is port 138 and 139 used for?

These ports are used for NetBIOS services in Windows environments, related to file and printer sharing.

What is the difference between POP3 and IMAP ports?

POP3 (port 110) downloads emails to a single device, while IMAP (port 143) allows access from multiple devices by storing emails on the server.

Can I block ports on a firewall?

Yes, firewalls can block specific ports to restrict unauthorized services or potential threats.

How do I check open ports on my network?

You can use tools like Nmap, Netstat, or online scanners to identify open ports on your system or network.

Are all ports safe to use?

No, unused or vulnerable ports can be exploited by hackers. Only open the ports you absolutely need and monitor them regularly.

What is the use of port 161?

Port 161 is used by SNMP to manage and monitor network devices like routers and switches.

How do hackers exploit open ports?

Hackers scan networks for open ports and exploit vulnerable services running on those ports to gain unauthorized access.

Why should you secure common network ports?

Securing ports reduces your network’s attack surface and helps prevent cyberattacks such as data breaches and malware infections.

What port does HTTPS use?

HTTPS, which provides encrypted and secure web access, uses port 443.

Can ports be changed manually?

Yes, administrators can configure services to run on non-default ports to obscure them from attackers.

What is a closed vs open port?

An open port is listening for incoming traffic; a closed port is not active or accepting connections.

What is the best tool to scan open ports?

Nmap is one of the most powerful and widely used tools for scanning open ports and services.