How to Check if My RDP is Using Port 25

How to Check if My RDP is Using Port 25? Step-by-Step Guide

/ Knowledgebase, Remote Desktop Protocol (RDP)

Remote Desktop Protocol (RDP) is a powerful tool that permits users to access a computer remotely. By default, RDP uses port 3389, but there might be instances where you need to check if RDP is using another port, such as port 25. This blog will guide you through how to check if my RDP is using port 25, why this is important, and what to do if you need to change it.

Why Check if RDP is Using Port 25?

Port 25 is traditionally used for SMTP (Simple Mail Transfer Protocol), which is responsible for sending emails. Many internet service providers (ISPs) block port 25 to prevent spam. If your RDP is configured to use port 25, it may cause connectivity issues, or your ISP may block it altogether.

Methods to Check if Your RDP is Using Port 25

There are several ways to determine which port your RDP is using. Below are the most effective methods:

1. Check the RDP Port in the Windows Registry

One of the simplest ways to check the port used by RDP is through the Windows Registry.

Steps to Check RDP Port in the Registry:

  1. Press the Windows button + R to open the Start dialog box.
  2. Write regedit & press Submit to open the Registry Editor.
  3. Navigate to the following key:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp
  4. Look for the entry named PortNumber.
  5. If the value of PortNumber is 25, then your RDP is using port 25.

If the port number is different (such as 3389), your RDP is not using port 25.

2. Use PowerShell to Check RDP Port

PowerShell is a powerful tool for checking network configurations.

Steps to Check RDP Port Using PowerShell:

  1. Open PowerShell as Administrator.
  2. Run the following command:
    Get-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp' -Name PortNumber
  3. The output will show the current RDP port. If it displays 25, then your RDP is using port 25.

3. Check RDP Port Using Command Prompt (Netstat)

You can also use Netstat to check which port RDP is using.

Steps to Check RDP Port Using Netstat:

  1. Open Command Prompt as Administrator.
  2. Run the command:
    netstat -an | find "LISTEN"
  3. Look for an entry that includes 0.0.0.0:25 or ::25. If you see this, RDP is using port 25.

4. Use Nmap or Online Port Scanner

If you have access to another device, you can use Nmap or an online port scanner to check if RDP is running on port 25.

Using Nmap (Requires Installation):

  1. Install Nmap if you haven’t already.
  2. Open a terminal or command prompt.
  3. Run the command:
    nmap -p 25 <Your-IP-Address>
  4. If port 25 is open and associated with RDP, the output will indicate this.

Using an Online Port Scanner:

  1. Go to a website like https://www.yougetsignal.com/tools/open-ports/.
  2. Enter your IP address.
  3. Type 25 as the port number and scan.
  4. If port 25 is open, your RDP might be using it.

What to Do If RDP Is Using Port 25?

If you find that RDP is using port 25, you may want to change it to avoid conflicts with email servers and ISP restrictions.

How to Change RDP Port to a Different Port

Modify the Windows Registry to Change RDP Port:

  1. Open Registry Editor (regedit).
  2. Navigate to:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp
  3. Double-click PortNumber.
  4. Select Decimal and enter a new port number (e.g., 3389 or any port above 1024).
  5. Click OK and restart your computer.

Allow the New Port in Windows Firewall:

  1. Open Windows Defender Firewall.
  2. Go to Advanced Settings.
  3. Click Inbound Rules > New Rule.
  4. Select Port, click Next.
  5. Enter the new port number and allow the connection.
  6. Apply the rule and restart the system.

Security Considerations When Changing RDP Ports

If you decide to change your RDP port, consider these security best practices:

  • Use Strong Passwords: Ensure that your RDP login credentials are secure.
  • Enable/On Network Level Authentication (NLA): This adds an extra layer of security.
  • Use a VPN: Avoid exposing RDP directly to the internet.
  • Limit RDP Access: Configure firewall rules to allow access only from trusted IP addresses.
  • Monitor RDP Activity: Use Windows Event Viewer or third-party tools to track RDP logins.

Conclusion

Checking if your RDP is using port 25 is important, as this port is generally reserved for email traffic and may be blocked by ISPs. You can check your RDP port through the Windows Registry, PowerShell, Command Prompt, or third-party tools like Nmap. If your RDP is using port 25, it is recommended to change it to avoid connectivity issues and security vulnerabilities.

By following the steps outlined in this guide, you can ensure that your Remote Desktop connection is configured correctly and securely. If you are still facing issues, consider consulting your network administrator or IT support for assistance.

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