NAT Port Forwarding with rinetd - A Simple Guide

Introduction

In this guide, I will introduce you to rinetd, a powerful tool for NAT port forwarding. NAT port forwarding allows you to redirect incoming network traffic from one port to another, making it useful for various scenarios, such as accessing services behind a firewall or sharing resources across different networks. We will cover the installation, configuration, and restarting process of rinetd.

Installation

To install rinetd, open your terminal and enter the following command:

sudo apt install rinetd

Configuration

Once the installation is complete, we need to configure rinetd to specify the port forwarding rules. Open the rinetd configuration file using your preferred text editor:

sudo vim /etc/rinetd.conf

In the configuration file, you will see a sample rule commented out. Let's use it as an example and modify it to suit our needs. Each line in the configuration file represents a port forwarding rule and follows this format:

#source_address source_port destination_address destination_port

For instance, if we want to forward incoming traffic from port 3306 on all network interfaces to port 3306 on the destination address 172.17.16.29, we would add the following line to the configuration file:

0.0.0.0 3306 172.17.16.29 3306

Feel free to add more rules if needed, each on a separate line.

Restarting

After configuring rinetd, we need to restart the service for the changes to take effect. Execute the following command:

sudo systemctl restart rinetd

Now, any incoming traffic on the specified source port will be automatically redirected to the corresponding destination port. This can be extremely useful for scenarios where you need to expose services behind a firewall or share resources across different networks. Experiment with different configurations to suit your specific needs.