Setting Up Libreswan IPSec VPN Tunnel for Inter-Regional VPC on AWS EC2 Instances

Introduction

Establishing a secure site-to-site VPN tunnel between two Amazon Web Services (AWS) Virtual Private Clouds (VPCs) located in different regions is a critical task for many organizations. This article outlines the process of setting up such a tunnel using Libreswan IPSec on EC2 instances running a RHEL-based Linux distribution.

Prerequisites

Before starting, ensure you have:

• Two EC2 instances, one in each VPC.
• Public Elastic IPs (EIPs) assigned to each instance.
• Subnet details of the instances.
• Basic understanding of Linux command-line operations.

Script Overview

The provided script automates the installation and configuration of Libreswan IPSec to establish the VPN tunnel. The key components and steps are explained below.

Step-by-Step Setup

1. Initial Setup

1. Environment Variables: Define the necessary variables either by passing them as environment variables or directly replacing them in the script:

• PSK: Pre-shared key for IPSec.