How to Implement Virtual Private Network (VPN) Split Tunneling with Policy-Based Routing on Your Dedicated Server

Setting up VPN split tunneling with policy-based routing on a dedicated server can be a complex task and requires careful configuration. Below are general steps to guide you through the process. Keep in mind that the specific steps may vary depending on the operating system and VPN software you are using.

Prerequisites:

1. Access to a Dedicated Server: You should have access to a dedicated server with administrative privileges.
2. Installed VPN Software: Make sure you have a VPN server software installed on your dedicated server. OpenVPN or WireGuard are popular choices.
3. Basic Networking Knowledge: Understanding of networking concepts and familiarity with the command line interface (CLI) is beneficial.

Steps:

1. Connect to Your Server:Use SSH or any other remote access method to log in to your dedicated server with administrative privileges.
2. Install Necessary Software:If you haven't already, install the VPN server software of your choice. Follow the specific installation instructions for your chosen VPN software.
3. Configure VPN Server:Set up your VPN server as you normally would, including generating keys, certificates, and configuring the server's IP addresses.
4. Enable IP Forwarding:To allow traffic to pass through your server, you need to enable IP forwarding. This can be done by modifying a kernel parameter. Run the following command:bashCopy codesysctl -w net.ipv4.ip_forward=1
   To make this change permanent, edit /etc/sysctl.conf and add the line net.ipv4.ip_forward=1.
5. Configure Policy-Based Routing:This step involves setting up rules to route specific traffic through the VPN tunnel.
   • Identify the Subnet or IP Ranges:Determine which subnets or IP ranges should go through the VPN and which should use the regular internet connection. For example, you might want all traffic from 192.168.0.0/24 to use the VPN.
   • Create Routing Tables:Use the ip command to create additional routing tables. For example:bashCopy codeip rule add from 192.168.0.0/24 table 100
     This command adds a rule that routes traffic from the specified subnet through table 100.
   • Add Default Routes:In each routing table, add a default route that points to the VPN interface. For example:bashCopy codeip route add default via <VPN_GATEWAY_IP> dev <VPN_INTERFACE> table 100
     
6. Set Up NAT (Network Address Translation):If you want traffic leaving the server to appear as if it's coming from the server itself, you'll need to set up NAT. Use iptables or a similar tool to configure NAT rules.
7. Testing:Test your setup by connecting to the VPN from a client and verify if traffic is being split correctly based on your routing rules.
8. Automate on Boot:Make sure your routing and NAT configurations are applied on system startup. You can do this by adding the necessary commands to your startup scripts or using a tool like iptables-persistent.

Remember to consult the documentation of your specific VPN software and operating system for any additional steps or considerations. Always make backups and proceed with caution, as incorrect network configurations can potentially disrupt connectivity to your server.