Routing WAN Traffic with IPSEC Tunnel on OpenVPN Server (Debian)

Routing WAN Traffic over an IPsec Tunnel on an OpenVPN Server (Debian)

In this article, we will discuss the process of routing WAN traffic over an IPsec tunnel on a Debian server used as a WAN router. By the end of this article, you will have a good understanding of the reasons for and the process of configuring such a setup.

Why Route WAN Traffic over an IPsec Tunnel on a Debian Server?

There are various reasons for routing WAN traffic over an IPsec tunnel on a Debian server. One of the primary reasons is to enhance security by encrypting all WAN traffic. By using an IPsec tunnel, you can ensure that your data is protected from unauthorized access and eavesdropping. Additionally, IPsec tunnels can help you to meet compliance requirements for data security and privacy.

Prerequisites

Before we begin, it is assumed that you have a Debian server installed and configured as a WAN router. You should also have a basic understanding of networking concepts and be familiar with the command line interface of Debian. Finally, you should have an IPsec tunnel established between your Debian server and the remote network.

Configuring the Debian Server as a WAN Router

To route WAN traffic over an IPsec tunnel, you need to configure your Debian server as a WAN router. Here are the steps you need to follow:

1. First, you need to configure the network interfaces on your Debian server. You can do this by editing the /etc/network/interfaces file. Here is an example configuration:

   # This file describes the network interfaces available on your system
   # and how to activate them. For more information, see interfaces(5).
   
   # The loopback network interface
   auto lo
   iface lo inet loopback
   
   # The primary network interface
   auto eth0
   iface eth0 inet dhcp
   
   # The WAN interface
   auto eth1
   iface eth1 inet static
       address 192.168.1.1
       netmask 255.255.255.0
       gateway 192.168.1.10

2. Next, you need to configure the firewall rules on your Debian server. You can do this by editing the /etc/iptables/rules.v4 and /etc/iptables/rules.v6 files. Here is an example configuration:

   # This file contains the iptables rules for the IPv4 network
   
   *filter
   
   # Allow all traffic on the loopback interface
   -A INPUT -i lo -j ACCEPT
   -A OUTPUT -o lo -j ACCEPT
   
   # Allow all traffic on the WAN interface
   -A INPUT -i eth1 -j ACCEPT
   -A OUTPUT -o eth1 -j ACCEPT
   
   # Allow established connections
   -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
   
   # Allow traffic on the IPsec tunnel
   -A INPUT -i tun0 -j ACCEPT
   -A OUTPUT -o tun0 -j ACCEPT
   
   # Drop all other traffic
   -A INPUT -j DROP
   -A FORWARD -j DROP
   -A OUTPUT -j DROP

   # This file contains the iptables rules for the IPv6 network
   
   *filter
   
   # Allow all traffic on the loopback interface
   -A INPUT -i lo -j ACCEPT
   -A OUTPUT -o lo -j ACCEPT
   
   # Allow all traffic on the WAN interface
   -A INPUT -i eth1 -j ACCEPT
   -A OUTPUT -o eth1 -j ACCEPT
   
   # Allow established connections
   -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
   
   # Allow traffic on the IPsec tunnel
   -A INPUT -i tun0 -j ACCEPT
   -A OUTPUT -o tun0 -j ACCEPT
   
   # Drop all other traffic
   -A INPUT -j DROP
   -A FORWARD -j DROP
   -A OUTPUT -j DROP

3. Finally, you need to enable IP ```