Port Lookup Tool

Intro

Look up a TCP or UDP port number and see the service it is commonly associated with.

A port number helps identify which service or application is listening on a host. This tool is useful when you need a quick reference for common ports used by web servers, SSH, email, databases, remote access, and other network services.

It is especially useful when you want to:

• identify what a port is commonly used for
• understand firewall or security group rules
• troubleshoot blocked connections
• review server exposure
• verify service mappings during setup
• learn common port assignments faster

What Is a Port Number?

A port number identifies a specific network service running on a server or device.

IP addresses tell traffic which host to reach. Port numbers help determine which service on that host should receive the traffic.

This allows a single server to run multiple services at the same time, such as:

• a website on port 80 or 443
• SSH on port 22
• a database on port 3306
• email services on mail-related ports
• remote desktop on port 3389

Why Ports Matter

Ports matter because they let multiple services share one system without conflict.

They are important for:

• firewall rules
• router forwarding
• cloud security groups
• service troubleshooting
• exposure reviews
• application connectivity
• network documentation
• In practice, when a connection fails, one of the first things to check is whether:
• the right port is open
• the right service is listening
• the firewall allows traffic
• the client is targeting the expected port

Common Port Numbers

This tool is most useful when paired with quick context around the most common port assignments.

21 — FTP

Commonly used for:

• traditional file transfer
• legacy hosting environments
• some older automation workflows

FTP is widely known, but it is generally less secure than modern encrypted alternatives.

22 — SSH

Commonly used for:

• secure shell access
• remote Linux administration
• SCP and SFTP transfers
• automation and remote commands

This is one of the most important ports for Linux server management.

25 — SMTP

Commonly used for:

• mail transfer between servers
• outbound mail relay in some environments

Port 25 is often restricted by cloud providers and ISPs because of spam abuse concerns.

53 — DNS

Commonly used for:

• domain name resolution
• DNS queries
• authoritative or recursive DNS services

DNS can use both UDP and TCP depending on the query type and size.

80 — HTTP

Commonly used for:

• unencrypted web traffic
• website redirects
• legacy web access

Many sites now redirect port 80 traffic to HTTPS.

110 — POP3

Commonly used for:

• older email retrieval workflows
• mail client downloads from a server

143 — IMAP

Commonly used for:

• email access
• mailbox synchronization across devices

443 — HTTPS

Commonly used for:

• encrypted website traffic
• secure APIs
• web applications
• admin panels behind TLS

This is one of the most common public-facing ports on the internet.

3306 — MySQL

Commonly used for:

• MySQL and MariaDB database access

This port should usually be restricted rather than exposed publicly.

3389 — RDP

Commonly used for:

• Remote Desktop Protocol access to Windows systems

Because RDP is a high-value target, it should be protected carefully and not exposed unnecessarily.

Well-Known vs Registered vs Dynamic Ports

Port numbers are often grouped into general ranges.

Well-Known Ports

These are ports from:

• 0 to 1023

They are commonly associated with major services such as:

• SSH
• HTTP
• HTTPS
• DNS
• SMTP

Registered Ports

These are ports from:

• 1024 to 49151

They are often used by:

• application services
• databases
• vendor-assigned software
• custom server apps

Dynamic or Ephemeral Ports

These are ports from:

• 49152 to 65535

They are often used temporarily by client systems for outbound connections.

Understanding these ranges helps when reviewing firewall behavior or service bindings.

TCP vs UDP Ports

A port number alone does not tell the whole story. You also need to know the transport protocol.

TCP

TCP is commonly used when:

• reliable delivery matters
• web traffic is involved
• SSH sessions are used
• database connections require ordered delivery

Examples:

• 22/TCP
• 80/TCP
• 443/TCP
• 3306/TCP

UDP

UDP is commonly used when:

• low overhead matters
• small queries are common
• speed is more important than guaranteed delivery

Examples:

• 53/UDP for many DNS queries

Some services can use both TCP and UDP depending on the situation.

Common Port Lookup Use Cases

Firewall Troubleshooting

A port lookup helps you understand whether a blocked connection involves:

• SSH
• web traffic
• mail delivery
• database access
• remote desktop

This is useful when reviewing:

• ufw
• firewalld
• security groups
• router forwarding
• hosting firewall rules

Server Hardening

When reviewing exposed services, a port reference helps you identify what is actually reachable from the network.

This is useful for spotting:

• unnecessary exposure
• forgotten services
• risky admin ports
• database ports left open publicly

Network Documentation

A port lookup helps when documenting:

• what each service uses
• why a firewall rule exists
• which applications need access
• how systems communicate

Learning and Training

For Linux users, junior admins, and self-hosters, a port lookup tool is a quick way to learn what common services run on which ports.

How to Check Open Ports on Linux

The live page already includes these Linux commands:

ss -tulpn

and:

netstat -tulpn

These commands help you see:

• which ports are listening
• which protocols are in use
• which processes own the sockets

This is useful when you want to compare:

• what a service should be using
• what is actually listening
• what the firewall allows

Common Port-Related Problems

Service Not Listening

The firewall may be open, but the service itself is not running or not bound to the expected port.

Wrong Port in Client Configuration

A client may be trying to connect to the wrong port for the service.

Examples include:

• using HTTP on a TLS-only service
• using the wrong database port
• connecting to the wrong admin port

Firewall Blocking the Port

The service may be running, but a host firewall, cloud firewall, or upstream network rule blocks the traffic.

Public Exposure of Sensitive Ports

Some ports should not usually be open to the public internet.

Examples include:

• database ports
• admin interfaces
• RDP
• SSH without proper restrictions

Confusing Port With Service Health

A known port number only tells you what a service is commonly associated with. It does not guarantee that the service is healthy, secure, or configured correctly.

Best Practices for Port Reviews

When reviewing ports, it helps to:

• confirm both the port number and protocol
• check whether the service is actually listening
• verify firewall rules match the intended service
• minimize public exposure of admin ports
• avoid exposing databases directly unless required
• document why each open port is needed
• review external exposure regularly

For production systems, the safest rule is usually to expose only the ports that are truly necessary.

Frequently Asked Questions

What is a port number?

A port number is a numeric identifier used to direct network traffic to a specific service on a host.

What is port 22 used for?

Port 22 is commonly used for SSH and secure remote administration.

What is port 443 used for?

Port 443 is commonly used for HTTPS and encrypted web traffic.

Is port 3306 safe to expose publicly?

Usually no. Database ports are typically safer when restricted to trusted hosts or private networks.

What is the difference between TCP and UDP ports?

The same numeric port can be used with different transport protocols. TCP emphasizes reliable delivery, while UDP emphasizes lower overhead and speed.

How do I see what ports are open on Linux?

Common commands include:

ss -tulpn

or:

netstat -tulpn

Related Tools

You may also find these tools useful:

• TCP Port Tester
• DNS Lookup Tool
• HTTP Header Checker
• Nginx Config Generator
• CIDR / Subnet Calculator

Final Note

This Port Lookup Tool is useful for quickly identifying what a port is commonly used for and adding context to firewall, server, and networking decisions.

Use it as a quick reference, then pair it with service checks, firewall reviews, and socket inspection so you can troubleshoot connectivity more accurately.