How to forward a port with iptables

How to forward a port with iptables

Forward incoming traffic from one port to another host or port using iptables DNAT and PREROUTING rules.

Prerequisites

• Root access on a Linux system with iptables.
• IP forwarding enabled ( net.ipv4.ip_forward = 1).

Step-by-Step: Forward a Port with iptables

1. Enable IP forwarding:

   sudo sysctl -w net.ipv4.ip_forward=1

2. Add a DNAT rule to the PREROUTING chain. iptables redirects incoming TCP traffic on port 8080 to an internal host on port 80:

   sudo iptables -t nat -A PREROUTING -p tcp --dport 8080 -j DNAT --to-destination 192.168.1.100:80

3. Add a FORWARD rule to allow the forwarded traffic:

   sudo iptables -A FORWARD -p tcp -d 192.168.1.100 --dport 80 -j ACCEPT

4. Add a MASQUERADE rule so return traffic routes correctly:

   sudo iptables -t nat -A POSTROUTING -j MASQUERADE

How to Verify Port Forwarding with iptables

List the NAT rules to confirm the DNAT entry:

sudo iptables -t nat -L -n -v

Test from an external client:

curl http://{SERVER_PUBLIC_IP}:8080