How to Redirect Ports on a Linux Server

Port redirection allows traffic coming to one port to be forwarded to another. This is commonly used for running services on non-standard ports, Docker containers, Node.js apps, or game servers on a VPS.

Step 1: Check the Current Listening Port

Before redirecting, confirm which port your service is listening on.

ss -tulnp

Example: your app is listening on port 3000 and you want users to access it via port 80.

Step 2: Enable IP Forwarding (Required)

Port redirection requires IP forwarding to be enabled.

sudo sysctl -w net.ipv4.ip_forward=1

To make it permanent:

echo "net.ipv4.ip_forward=1" | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

Step 3: Redirect Port Using iptables

Redirect incoming traffic from port 80 to port 3000.

sudo iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 3000

This works instantly without restarting any service.

Step 4: Allow Traffic Through the Firewall

If UFW is enabled, allow both ports.

sudo ufw allow 80/tcp
sudo ufw allow 3000/tcp

Reload firewall rules if needed:

sudo ufw reload

Step 5: Verify Port Redirection

Check active NAT rules:

sudo iptables -t nat -L -n -v

Test from the server:

curl http://localhost

If configured correctly, traffic to port 80 will be served by port 3000.

Step 6: Make iptables Rules Persistent

iptables rules reset after reboot unless saved.

sudo apt install iptables-persistent -y
sudo netfilter-persistent save

This ensures port redirection survives server restarts.

Optional Step: Redirect a Different Port

Example: redirect port 443 to 8443.

sudo iptables -t nat -A PREROUTING -p tcp --dport 443 -j REDIRECT --to-port 8443

Useful for SSL apps, control panels, or Docker-based services.