Are you concerned about the security of your Linux system? As a system administrator, securing your system against potential threats is a top priority. One crucial component of security is SSH (Secure Shell), which provides a secure way to access your Linux system remotely. By default, SSH uses port 22 for incoming connections, but this default setting can pose a security risk. Hackers and malicious bots often target port 22 to gain unauthorized access. In this article, we will explore how to change the default SSH port to a specific port number to enhance the security of your Linux system.

Reasons to Change the Default SSH Port

The default SSH port is a well-known port (port 22) that is commonly targeted by hackers and malicious bots. Changing the default SSH port can help prevent these attacks, making it harder for attackers to find the port used for SSH. By changing the port, you add an extra layer of security to your system.

Choosing a Specific Port Number

When choosing a specific port number for SSH, it’s best to select a high port number that is not already in use. High port numbers are those above 1024 and are less likely to be used by other applications. However, you should avoid using a well-known port or a port number that is already in use.

Another advantage of using high port numbers is that they are less likely to be blocked by firewalls. Some network administrators block traffic to low port numbers to prevent certain types of attacks. By using a high port number, you can avoid being caught by these restrictions.

It’s crucial to follow best practices when selecting a specific port number. For example, you should avoid using sequential port numbers since attackers can easily guess the next port number in sequence. Instead, use a random number generator to select a unique port number.

Configuring SSH to Listen on the Specific Port

Once you have selected a specific port number, the next step is to configure SSH to listen on that port. The SSH daemon configuration file is located at /etc/ssh/sshd_config. To make changes to this file, you need to have root access to the system.

To begin the configuration process, open the sshd_config file using a text editor. Look for the line that says “# Port 22” and remove the “#” symbol. Then, change the number “22” to the specific port number you have chosen. Save the changes and close the file.

After making changes to the configuration file, restart the SSH daemon to apply the changes. You can do this by running the following command:

sudo service ssh restart

Testing the SSH Connection on the New Port

Once you have configured SSH to listen on the new port, it’s time to test the connection. To test the SSH connection, use the ssh command followed by the username and hostname of the remote system. Specify the port number using the -p option. For example:

ssh -p 2222 username@hostname

If the connection is successful, you will be prompted for your password or passphrase if you are using key-based authentication. If the connection fails, you may need to troubleshoot common connection issues.

Updating Firewall Rules

Changing the SSH port will require updating firewall rules that allow SSH traffic. If you are using a firewall tool such as iptables or firewalld, you will need to update the rules to allow traffic on the new port.

To update firewall rules, you need to know the syntax of the firewall tool you are using. For example, to allow incoming traffic on port 2222 using iptables, you can use the following command:

sudo iptables -A INPUT -p tcp --dport 2222 -j ACCEPT

Make sure to save the changes to the firewall rules to apply the changes.

Additional Security Measures

In addition to changing the default SSH port, there are other security measures you can take to further secure your SSH connections.

One of the most effective measures is to use key-based authentication instead of passwords. Key-based authentication is more secure than password authentication since it uses public and private key pairs to authenticate users. This method is also more convenient since you don’t need to remember a password.

Another security measure is to disable root login and create a new administrative user. This prevents attackers from using the root account to gain access to your system. By creating a new administrative user, you can provide access to the system without granting root privileges.

Finally, you can use tools such as fail2ban to detect and block malicious login attempts. Fail2ban monitors log files for failed login attempts and blocks IP addresses that exceed a certain threshold.

Best Practices for SSH Security

To maintain a secure SSH configuration, it’s important to follow best practices for SSH security. Some tips for maintaining a secure SSH configuration include:

• Regularly updating your SSH software to ensure that you have the latest security patches
• Using strong passwords or key-based authentication
• Disabling root login and creating a new administrative user
• Limiting the number of users who have access to SSH
• Configuring SSH to use only the most secure algorithms
• Using additional security measures such as fail2ban to detect and block malicious login attempts

Case Study: The Importance of Changing the Default SSH Port

As a system administrator for a small company, John was tasked with securing their Linux server. One of the first steps he took was changing the default SSH port from 22 to a high port number.

After making the change, John noticed a significant drop in the number of failed login attempts in the server logs. Prior to changing the port, the logs were filled with failed login attempts from various IP addresses. The majority of these attempts were from bots and scripts attempting to brute force their way into the server via the default SSH port.

John also implemented additional security measures such as key-based authentication, disabling root login, and using fail2ban to block malicious login attempts. However, he found that changing the default SSH port was one of the most effective measures he could take to enhance the server’s security.

By changing the port, John was able to effectively block most automated attacks while still allowing legitimate users to access the server via SSH. He noted that while it is still important to implement other security measures, changing the default SSH port is a simple and effective way to safeguard a Linux system.

Conclusion

Changing the default SSH port to a specific port number is an essential step in securing your Linux system against potential threats. By using a high port number that is not already in use and following best practices for SSH security, you can add an extra layer of security to your system. Remember to update firewall rules and test the SSH connection on the new port, and consider implementing additional security measures such as key-based authentication and fail2ban. By taking these steps, you can safeguard your Linux system and provide secure remote access for system administrators.

Questions and Answers

Question: What is SSH?

Answer: SSH is a secure protocol used for remote access to Linux servers.

Question: How do I enable SSH on a specific port?

Answer: Edit the /etc/ssh/sshd_config file and change the Port setting.

Question: Who can use SSH on a specific port?

Answer: Anyone with valid credentials and the correct port number can access the server.

Question: What if I can’t connect to the server after changing the port?

Answer: Ensure that the firewall allows traffic on the new port and that the client is using the correct port number.

Question: How can I test if SSH is working on the new port?

Answer: Use the command “ssh -p [port number] [username]@[server IP]” to connect to the server on the new port.

Question: What if I forget the new SSH port number?

Answer: Use a console or terminal to access the server and check the /etc/ssh/sshd_config file for the Port setting.