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A reverse SSH tunnel lets you access a machine behind NAT or a restrictive firewall — one that can't normally accept inbound connections — by having that machine initiate an outbound connection to a publicly reachable server instead.

The Problem This Solves

A machine on a home network or behind a corporate firewall typically can't be reached directly from the internet. A reverse tunnel flips the direction: the hard-to-reach machine connects out to your VPS, which then acts as a relay point you can connect through.

Basic Concept

[Hard-to-reach machine] —(outbound SSH connection)→ [Your VPS] —(you connect here)→ [access relayed back to the machine]

Prerequisites

• A VPS with a public IP, reachable from both ends
• SSH access from the hard-to-reach machine to the VPS

Step 1 — Establish the Reverse Tunnel (Run on the Hard-to-Reach Machine)

ssh -R 2222:localhost:22 tunnel-user@YOUR_VPS_IP -N

This forwards port 2222 on the VPS to port 22 (SSH) on the local machine running this command. -N means don't execute a remote command, just establish the tunnel.

Step 2 — Configure the VPS to Accept the Tunnel

sudo nano /etc/ssh/sshd_config

GatewayPorts yes

sudo systemctl restart sshd

GatewayPorts yes allows the forwarded port to be reachable from outside the VPS itself, not just from localhost on the VPS — needed if you'll be connecting from a third machine, not the VPS itself.

Step 3 — Connect Through the Tunnel

From anywhere, connect to the VPS on the forwarded port to reach the remote machine:

ssh -p 2222 user@YOUR_VPS_IP

Making the Tunnel Persistent (autossh)

A manually-run tunnel drops if the connection is interrupted. Use autossh to automatically reconnect:

sudo apt install autossh -y

autossh -M 0 -R 2222:localhost:22 tunnel-user@YOUR_VPS_IP -N -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3"

Running the Tunnel as a systemd Service (On the Remote Machine)

sudo nano /etc/systemd/system/reverse-tunnel.service

[Unit]
Description=Reverse SSH Tunnel
After=network.target

[Service]
ExecStart=/usr/bin/autossh -M 0 -R 2222:localhost:22 tunnel-user@YOUR_VPS_IP -N -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3"
Restart=always
User=tunneluser

[Install]
WantedBy=multi-user.target

sudo systemctl enable --now reverse-tunnel

Securing the Tunnel User Account

Create a dedicated, restricted account on the VPS specifically for accepting this tunnel connection — see How to Set Up a Deployment User with Restricted SSH Access for the general pattern of a minimal-privilege account, applied here to the tunnel user rather than a deployment context.

Forwarding Other Services (Not Just SSH)

ssh -R 8080:localhost:80 tunnel-user@YOUR_VPS_IP -N

Forwards a web service running on port 80 of the remote machine, reachable via port 8080 on the VPS.

Common Errors

Tunnel connects but the forwarded port isn't reachable externally — verify GatewayPorts yes is set and sshd was restarted.

Tunnel drops periodically — use autossh with keepalive options rather than a plain ssh command, which doesn't automatically reconnect after a drop.

Best Practices

• Use a dedicated, restricted account for the tunnel connection, not a general-purpose one
• Use autossh with keepalive settings for reliability rather than a manually-run tunnel
• Restrict which ports/services are forwarded to only what's genuinely needed

Continue Reading

• How to Set Up a Deployment User with Restricted SSH Access
• How to Secure SSH: Key-Based Authentication & Disabling Root Login
• How to Set Up a VPN Server with WireGuard

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