Remote Access Behind Firewalls and Routers
Accessing a device remotely behind a router can be challenging, especially when dealing with SSH connections. Whether you're trying to connect to a device from outside your LAN, understanding how to set up remote SSH behind router is essential for system administrators, developers, and IoT enthusiasts.
This guide will walk you through methods to enable remote SSH behind firewall, secure the connection, and troubleshoot common issues—without compromising security.
What Blocks Remote SSH Access?
Most routers and firewalls are configured by default to block incoming connections from the internet to internal devices. This is good for security but creates obstacles when you need to:
Access a Raspberry Pi at home from work
Manage internal devices from the outside
Monitor home IoT devices
Firewalls and NAT (Network Address Translation) obscure the internal network, making remote access behind firewall seem impossible—yet there are solutions.
Use Port Forwarding to Enable Remote Access
Port forwarding is the most common method to allow remote access behind router.
✅ How It Works:
Log in to your router’s admin interface
Go to Port Forwarding or Virtual Server settings
Forward an external port (e.g., 2222) to your internal device’s port 22 (SSH)
Example:
Router WAN IP: 203.0.113.15
Forward external port 2222 → internal IP 192.168.1.100:22
Then, from outside the network:
bash
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ssh [email protected] -p 2222
⚠️ Considerations:
Use a non-standard external port for better security (e.g., 2222 instead of 22)
Ensure firewall rules allow traffic on the forwarded port
Dynamic IP? Use Dynamic DNS (DDNS) for easier access
Method 2: Reverse SSH Tunnel
When you can't control the router or firewall (e.g., at a client site), use a reverse SSH tunnel.
✅ How It Works:
Your internal device initiates the SSH connection to a public server (you control)
This opens a reverse port tunnel from the server back to your internal device
On the internal device (behind NAT/firewall):
bash
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ssh -R 2222:localhost:22 [email protected]
From your remote PC:
bash
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ssh -p 2222 [email protected]
???? Advantages:
Works without modifying the firewall or router
Keeps connection outbound-only (more secure)
Ideal for remote support or hard-to-reach devices
Connect Securely with a VPN
Another reliable method for remote access behind firewall is setting up a VPN (Virtual Private Network).
✅ Options:
OpenVPN
WireGuard
IPSec
Commercial VPN services with port forwarding
Once connected to the VPN, your device becomes part of the internal network, allowing direct SSH access like this:
bash
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ssh [email protected]
????️ Benefits:
End-to-end encryption
No need to expose ports
Access multiple devices over LAN
Setting up your own VPN server (e.g., on a VPS or cloud) gives full control and flexibility.
Use Cloud-Based SSH Access Services
Several tools and platforms simplify SSH tunneling using encrypted, cloud-managed connections.
Popular Options:
Tailscale – Easy-to-use VPN based on WireGuard
ZeroTier – Mesh VPN with virtual LAN
Ngrok – Tunnels local ports to the internet
Remote.it – SSH proxy via cloud without port forwarding
These tools work by creating secure relay tunnels, meaning:
No need to configure router
No static IP required
Great for developers, small teams, and temporary access
Protecting Your Network While Enabling Access
???? Best Practices:
Disable root SSH login
Use SSH key authentication, not passwords
Change default port from 22 to a higher port (e.g., 2222)
Enable firewall rules to limit SSH access by IP
Use Fail2Ban or similar to prevent brute-force attacks
Keep SSH and server software up to date
Whether you use port forwarding, VPN, or tunneling, always prioritize security when setting up remote SSH behind firewall.
What to Do Without a Static IP
If your home or office uses dynamic IP addresses, it becomes difficult to connect from outside. Dynamic DNS (DDNS) solves this.
How It Works:
Sign up with DDNS provider (e.g., No-IP, DynDNS)
Link your WAN IP to a hostname like yourname.ddns.net
Set your router to auto-update the IP
Now, instead of typing your IP, connect like this:
bash
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ssh [email protected] -p 2222
Fixing Remote SSH Problems
Can’t connect to SSH?
Is the port forwarding active?
Is firewall allowing incoming connections?
Is the internal IP static or dynamic?
Is SSH service running remote access behind router on the target device?
Tools for Debugging:
nmap to scan open ports
ping to check connectivity
ssh -v for verbose connection output
Check logs (/var/log/auth.log) on the target system for authentication errors.
Who Needs Remote Access?
???? System Administrators
Manage Linux servers, IoT devices, routers, or remote installations from anywhere.
Developers
Deploy code, debug errors, and access test environments without physical presence.
Home Users
Access Raspberry Pi, NAS, or home automation tools when away.
Remote Workers
Secure access to internal company infrastructure using VPN or secure tunnels.
Best Tools and Software for SSH Remote Access
Tool Description Use Case
OpenSSH Built-in SSH client/server Universal, default tool
Ngrok Secure tunnel to local port Temporary access, development
Tailscale Easy mesh VPN with ACL control Team networks, BYOD
ZeroTier Virtual LAN for any device IoT, global access
Remote.it SSH proxy without static IP No port forwarding needed
Each tool fits different needs based on complexity, security, and budget.
Conclusion
Setting up remote access behind firewall doesn’t have to be overwhelming. Whether you choose port forwarding, reverse SSH tunneling, VPN, or cloud-based tools, there’s a solution to match your skill level and security requirements.
Always remember to:
Secure SSH connections
Limit access to trusted IPs
Regularly update software and keys
With the right setup, you can safely manage devices across networks—without opening your infrastructure to unnecessary risks.