How To: SSH Raspberry Pi Through A Firewall (Easy Steps)

vanessa

26 Apr, 2025

Are you struggling to remotely access your Raspberry Pi, tucked safely behind your home or office firewall? The ability to securely connect to your Raspberry Pi from anywhere in the world, even when shielded by a firewall, is not just a desirable feature; it's a critical necessity for many modern projects and applications, enabling remote monitoring, control, and data access.

For anyone working with embedded systems, home automation, or even just experimenting with the Internet of Things, the Raspberry Pi has become a cornerstone. Its versatility and affordability make it perfect for a multitude of tasks. However, its usefulness is significantly hampered if you cant access it remotely. Firewalls, designed to protect networks from unauthorized access, often pose a challenge to this very accessibility. This article delves into the techniques and technologies you can employ to successfully and securely SSH into your Raspberry Pi, bypassing the common hurdles that firewalls present. From understanding the fundamentals of network address translation (NAT) to employing sophisticated solutions like reverse SSH tunnels and VPNs, we'll explore a range of practical approaches that will empower you to maintain seamless remote access to your Pi.

Subject	Details
Project Name:	Securing Raspberry Pi Access Through Firewalls
Date:	October 26, 2023
Location:	Global (Applicable anywhere with internet access)
Objective:	To provide a comprehensive guide to establish and maintain secure SSH connections to a Raspberry Pi device, even when it's behind a firewall.
Target Audience:	Hobbyists, System Administrators, IoT developers, and anyone who needs to remotely access their Raspberry Pi.
Key Technologies:	SSH, Firewall Rules, Port Forwarding, NAT, Reverse SSH Tunnels, VPNs, Dynamic DNS, SSH Key Authentication.
Challenges Addressed:	Network Address Translation (NAT), Firewall Restrictions, Dynamic IP Addresses, Security vulnerabilities.
Reference:	Raspberry Pi Official Website

The first, and often simplest, method for accessing your Raspberry Pi is by using port forwarding. Most home routers utilize Network Address Translation (NAT). NAT allows multiple devices on your internal network to share a single public IP address. When you connect to the internet, your router translates the internal IP address of your Raspberry Pi (e.g., 192.168.1.100) into its public IP address. Port forwarding involves configuring your router to direct incoming traffic on a specific port (usually port 22 for SSH) to the internal IP address of your Raspberry Pi. Essentially, this creates a direct path through the firewall for SSH connections. This approach is often the easiest to implement, however, it also comes with some security considerations that must be addressed.

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To set up port forwarding, youll need to access your routers configuration page. This is typically done by entering the router's IP address (often 192.168.1.1 or 192.168.0.1) into a web browser. You'll then need to log in with your router's username and password. Once logged in, you should look for a section labeled "Port Forwarding," "Virtual Servers," or something similar. Within this section, you'll need to create a new rule, specifying the following information:

Service Name: This is just a label for the rule, like "SSH Raspberry Pi."
Protocol: Select "TCP" (SSH uses the TCP protocol).
External Port: This is the port you want to use to access your Pi from the outside. It's common to use port 22, but for security reasons, you might choose a different, less common port (e.g., 2222).
Internal Port: This should be set to 22 (the standard SSH port on the Raspberry Pi).
Internal IP Address: Enter the internal IP address of your Raspberry Pi (e.g., 192.168.1.100).

After saving the rule, you should be able to SSH into your Raspberry Pi from outside your network using the external port you configured. For instance, if you chose port 2222, you would connect using the command: `ssh pi@your_public_ip_address -p 2222`. Replace `your_public_ip_address` with your router's public IP address. You can find your public IP address by searching on the internet for "what is my IP address".

However, the dynamic nature of IP addresses poses a significant challenge. Most internet service providers (ISPs) assign dynamic IP addresses, meaning your public IP address can change periodically. This makes it difficult to consistently connect to your Raspberry Pi using port forwarding. To overcome this, you can use a Dynamic DNS (DDNS) service. DDNS services provide a hostname that always points to your current public IP address. You configure the DDNS service on your router or directly on your Raspberry Pi using a client that updates the hostname whenever your IP address changes.

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Several DDNS services are available, such as No-IP, DuckDNS, and DynDNS (paid service). To use a DDNS service, you typically need to:

Sign up for an account: Choose a DDNS provider and create an account.
Configure a hostname: Create a hostname (e.g., myraspberrypi.ddns.net) that you will use to access your Pi.
Configure your router or Raspberry Pi: Most routers have built-in DDNS client support. If your router doesn't, you can install a DDNS client on your Raspberry Pi. The client will automatically update your hostname with your current public IP address.

With a DDNS service in place, you can now use your hostname instead of your public IP address when SSHing into your Pi. For example: `ssh pi@myraspberrypi.ddns.net -p 2222`. This ensures that you can always connect to your Pi, even if your public IP address changes. This combination of port forwarding and Dynamic DNS provides a robust and accessible solution for many users.

While port forwarding with DDNS offers a relatively straightforward solution, it does have security implications. By opening a port on your firewall, you're potentially exposing your Raspberry Pi to the wider internet. This makes it crucial to implement strong security measures.

One of the most fundamental security measures is to change the default password for the `pi` user. The default password is `raspberry`, and leaving it unchanged is a major security risk. To change the password, SSH into your Pi (either directly or through port forwarding) and use the command: `passwd`. You'll be prompted to enter the current password (if applicable) and then a new password twice. Choose a strong, unique password, and make sure you can remember it.

Beyond changing the password, consider disabling password authentication altogether and using SSH key-based authentication. This is a much more secure method of authentication. With key-based authentication, you generate a public/private key pair. You then copy the public key to your Raspberry Pi. When you connect via SSH, your client uses your private key to authenticate. This is much more secure than relying on a password, as it prevents brute-force attacks.

To set up key-based authentication:

Generate an SSH key pair on your local machine: If you're using Linux or macOS, you can open a terminal and run `ssh-keygen`. For Windows, you can use a tool like PuTTYgen (which comes with PuTTY). Follow the prompts, choosing a strong passphrase for your private key.
Copy the public key to your Raspberry Pi: Use the command `ssh-copy-id pi@your_raspberry_pi_ip_address` (replace `your_raspberry_pi_ip_address` with your Pi's IP address or hostname). You will be prompted for the `pi` user's password. This command copies your public key to the `~/.ssh/authorized_keys` file on the Pi.
Disable password authentication (optional but recommended): After successfully setting up key-based authentication, you can disable password authentication to further enhance security. Edit the SSH configuration file on your Pi: `sudo nano /etc/ssh/sshd_config`. Find the line `PasswordAuthentication yes` and change it to `PasswordAuthentication no`. Also, consider changing `PermitRootLogin yes` to `PermitRootLogin no` (if you don't require root login over SSH) and set a `Port` number other than 22 (example 2222). Then, restart the SSH service: `sudo systemctl restart ssh`.

Furthermore, always keep your Raspberry Pi's operating system and software up to date. Regularly run `sudo apt update` and `sudo apt upgrade` to install security patches and updates. Regularly audit logs for any suspicious activity.

Another powerful method for accessing your Raspberry Pi is through reverse SSH tunnels. This is particularly useful if you can't directly configure your router for port forwarding (e.g., if you're behind a very restrictive firewall or in a network where you don't have administrative access). With a reverse SSH tunnel, your Raspberry Pi initiates the SSH connection to a server that you control (or have access to). Then, you can connect to that server, which will forward the connection to your Raspberry Pi, essentially tunneling the SSH connection through the firewall.

To set up a reverse SSH tunnel, you'll need a server with a public IP address. This could be a cloud server (like an AWS EC2 instance, a Google Compute Engine instance, or a DigitalOcean droplet) or a server you already have access to. The server must have SSH enabled. The process involves setting up the tunnel on your Pi.

The general steps involve:

Set up a server: Have a server with a public IP address and SSH access.
SSH into your server from the Raspberry Pi: From your Raspberry Pi, establish an SSH connection to your server, including the `-R` flag to specify a reverse tunnel. The basic command looks like this: `ssh -R 2222:localhost:22 user@your_server_ip_address`. Replace `2222` with the port you want to use on the server (this is the port you'll connect to on the server to access your Pi), `user` with your username on the server, and `your_server_ip_address` with the server's IP address. The `localhost:22` part specifies that the tunnel should forward traffic to port 22 (the SSH port) on your Raspberry Pi. If you are using key-based authentication with the server, the command will run even more smoothly.
Connect to your Raspberry Pi through the tunnel: From your local machine (not your Pi), connect to your server using SSH, but this time specifying the port you chose for the reverse tunnel. The command will be something like: `ssh user@your_server_ip_address -p 2222`. This will connect you to your Raspberry Pi. You can then log into your Raspberry Pi as you would normally.

The `-R` flag in the SSH command tells SSH to create a reverse tunnel. This tunnel is created from the Raspberry Pi to the server, allowing connections initiated on the server to be forwarded to the Pi. This avoids the need to open ports on your home router, as the Pi is initiating the connection to the outside. This is extremely useful when the Raspberry Pi is in a network that doesn't allow inbound connections.

There are a number of advanced configurations that can be used with reverse SSH tunnels. You can, for example, use multiple tunnels for different services running on the Raspberry Pi. Moreover, you can configure the tunnel to automatically reconnect if the connection is lost by using tools like `autossh`. `autossh` will continually monitor the SSH connection and reopen it automatically if it drops. This makes reverse SSH tunnels far more reliable for production environments.

A third option for accessing your Raspberry Pi is through a Virtual Private Network (VPN). A VPN creates an encrypted tunnel between your device and a VPN server. When you connect to the VPN, your device appears to be on the same network as the VPN server. This allows you to access your Raspberry Pi as if you were directly connected to its network. This is a very secure method that encapsulates all traffic.

Setting up a VPN for your Raspberry Pi involves several steps, including selecting a VPN server, configuring the server, and configuring the client on both the Raspberry Pi and your local device.

There are various VPN protocols available, including OpenVPN, WireGuard, and IPsec. OpenVPN is a popular choice due to its versatility and wide support. WireGuard, a newer protocol, offers better performance and enhanced security, but requires a more modern kernel. Choosing between these depends on your specific needs and the capabilities of your devices.

Here's a simplified guide for setting up a VPN using OpenVPN:

Choose a VPN Server: You can either use a commercial VPN provider or set up your own VPN server on another machine (e.g., a cloud server). If you choose a commercial provider, you'll usually need to subscribe to their service. If setting up your own, you'll need a server with a public IP address.
Install OpenVPN on your Raspberry Pi: Connect to your Raspberry Pi via SSH and install OpenVPN and the necessary configuration tools using: `sudo apt update` followed by `sudo apt install openvpn easy-rsa`.
Generate VPN Server Certificates and Keys (if setting up your own server): This is a crucial step for securing your VPN connection. You'll need to use Easy-RSA (or a similar tool) to generate the certificates and keys for your VPN server and your client (your Raspberry Pi).
Configure the OpenVPN Server (if applicable): Configure the OpenVPN server on your Raspberry Pi. This involves editing the server configuration file (`/etc/openvpn/server.conf` or similar), specifying the network settings, the certificates to use, and other options.
Configure the OpenVPN Client on your Raspberry Pi: Create a client configuration file (`.ovpn` file) that contains the necessary settings to connect to your OpenVPN server. This typically includes the server's IP address or hostname, the port number, and the client certificate.
Configure the client on your local machine: Install an OpenVPN client application (like OpenVPN Connect or Tunnelblick) on your local machine. Import the `.ovpn` configuration file you created, and connect to the VPN.
Test the Connection: Once the VPN connection is established, you should be able to access your Raspberry Pi through its internal IP address (e.g., 192.168.1.100), as if you were on the same network.

With a VPN in place, you can connect to your Raspberry Pi securely, regardless of where you are. All traffic between your device and your Raspberry Pi is encrypted, providing an extra layer of security. Setting up a VPN is generally more complex than port forwarding, but it offers the best level of security and flexibility.

When considering the best approach for accessing your Raspberry Pi through a firewall, there is no single "best" solution. The ideal method depends on your specific needs, technical expertise, and security requirements. Port forwarding with DDNS is often the easiest to set up but is less secure. Reverse SSH tunnels provide a more secure option when you can't directly configure your router. VPNs offer the most robust security but are more complex to configure. Remember that security is paramount. Always prioritize secure configuration, strong passwords, and keeping your system up-to-date. By understanding these options and following the guidelines provided, you can choose the method that best fits your needs and ensure secure remote access to your Raspberry Pi.