How to Find the Port Number of an IP Address

When working with networking or server-side applications, you may often need to identify the port number associated with a specific IP address. Port numbers are part of the address used to route data to the correct process or service on a machine. They serve as communication endpoints for network services like web servers, FTP servers, and databases.

Finding the port number of an IP address typically involves identifying which services or applications are running on that IP. This can be done using several tools and techniques.

In this article, we’ll explore different methods for finding the port number of an IP address.

What Are Port Numbers?

Port numbers are used in networking to specify particular processes or services on a machine. For example:

• HTTP (Web Servers) commonly uses port 80.
• HTTPS (Secure Web Servers) uses port 443.
• FTP (File Transfer Protocol) uses port 21.

Port numbers range from 0 to 65535, and they are divided into three categories:

• Well-known ports (0-1023): Reserved for common protocols like HTTP, FTP, and SSH.
• Registered ports (1024-49151): Used by specific applications or services that aren’t widely known.
• Dynamic/Private ports (49152-65535): Typically used for client-side communication and ephemeral connections.

Method 1: Using Netstat (Network Statistics)

The netstat command provides detailed information about active connections and open ports on your system. You can use this tool to find the local ports and their associated IP addresses.

Steps to find port number using netstat:

1. Open Command Prompt or Terminal:
   • On Windows, press Win + R, type cmd, and hit Enter to open Command Prompt.
   • On Linux/macOS, open the Terminal.
2. Run the netstat Command:
   • Type the following command and press Enter:
     bash

     netstat -an | findstr <IP_address>


     Replace <IP_address> with the IP address you’re interested in. For example:

     bash

     netstat -an | findstr 192.168.1.100

3. Analyze the Output:
   • The output will list active connections and open ports associated with that IP address. It will display entries in the following format:
     TCP 192.168.1.100:80 0.0.0.0:0 LISTENING
TCP 192.168.1.100:443 0.0.0.0:0 LISTENING


     Here, the port numbers 80 and 443 are being used by the IP 192.168.1.100.

Note: On some systems, you might need to use the sudo command on Linux/macOS to run netstat.

Method 2: Using Nmap (Network Mapper)

Nmap is a powerful open-source tool used for network discovery and security auditing. It can be used to scan an IP address for open ports and services.

Steps to find port numbers using Nmap:

1. Install Nmap:
   • On Windows, download and install Nmap from nmap.org.
   • On Linux/macOS, you can install Nmap via package managers like apt or brew.
2. Run the Nmap Command:
   • Open the terminal or command prompt.
   • Use the following command to scan a specific IP address for open ports:
     bash

     nmap <IP_address>


     Replace <IP_address> with the target IP you want to scan. For example:

     bash

     nmap 192.168.1.100

3. Analyze the Output:
   • Nmap will provide a list of open ports and the services associated with them. Example output:
     kotlin

     Starting Nmap 7.80 ( https://nmap.org ) at 2022-01-01 12:00 PST
Nmap scan report for 192.168.1.100
Host is up (0.0010s latency).
Not shown: 997 filtered ports
PORT STATE SERVICE
22/tcp open ssh
80/tcp open http
443/tcp open https
3306/tcp open mysql


Note: Nmap allows more advanced scanning options, such as scanning specific port ranges or using different scanning techniques. Use the nmap --help command for more details.

Method 3: Using Online Port Scanners

There are many online tools available that can scan an IP address and return a list of open ports. These tools are easy to use and don’t require installing anything on your local machine.

Steps to use an online port scanner:

1. Choose an Online Port Scanning Tool:
   • Some popular tools include:
     • YouGetSignal
     • Pingdom
     • Canyouseeme
2. Enter the IP Address:
   • Visit one of the port scanner websites and enter the IP address you want to check.
3. Start the Scan:
   • Click the “Check” or “Scan” button to start the process.
4. Review the Results:
   • The scanner will show you which ports are open and what services are running on them.

Note: Online tools may only be able to scan external (public) IP addresses. If you’re trying to scan a private IP or an internal network, you’ll need to use tools like Nmap or netstat.

Method 4: Using Telnet (Manual Connection Test)

If you know the port number but need to verify if a particular service is running on that port, you can use Telnet to manually connect to the port.

Steps to check a port with Telnet:

1. Open Command Prompt or Terminal:
   • On Windows, press Win + R, type cmd, and hit Enter.
   • On Linux/macOS, open the Terminal.
2. Run Telnet Command:
   • To test connectivity to a specific port on an IP address, use the following syntax:
     bash

     telnet <IP_address> <port_number>


     For example, to test if port 80 is open on IP 192.168.1.100, use:

     bash

     telnet 192.168.1.100 80

3. Analyze the Result:
   • If the port is open, you will see a successful connection message.
   • If the port is closed, you will receive a connection error.

Note: Telnet is not always installed by default. On Windows, you may need to enable it via “Turn Windows features on or off.”

Finding the port number of an IP address depends on the specific context (whether you control the IP or are scanning it remotely). Here are the main methods to determine open ports:

1. Use netstat on your local machine to find open ports.
2. Use Nmap to scan for open ports on an IP address.
3. Use online port scanners for a quick, external check.
4. Use Telnet to manually verify a connection to a specific port.

Port scanning and network exploration tools like Nmap and Telnet are invaluable for network administrators, security professionals, and developers working with network services.