OPENVPN - Multiple Server Processes to Combine Link Speeds

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Multiple_Server_Processes_to_Combine_Link_Speeds

Create Multiple OpenVPN Configuration Files

The first step is to create two separate OpenVPN server configurations, each bound to a different internet link. This will allow the OpenVPN process to listen on different interfaces for each connection.

Example `server1.conf`: 

port 1194
proto udp
dev tun
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt
push "route 10.8.0.0 255.255.255.0"
push "redirect-gateway def1"
ca /etc/openvpn/ca.crt
cert /etc/openvpn/server1.crt
key /etc/openvpn/server1.key
dh /etc/openvpn/dh2048.pem
server-bridge
push "dhcp-option DNS 8.8.8.8"
;bind to the first internet link's IP address
local 192.168.1.100

Example `server2.conf`: 

port 1195
proto udp
dev tun
server 10.8.1.0 255.255.255.0
ifconfig-pool-persist ipp.txt
push "route 10.8.1.0 255.255.255.0"
push "redirect-gateway def1"
ca /etc/openvpn/ca.crt
cert /etc/openvpn/server2.crt
key /etc/openvpn/server2.key
dh /etc/openvpn/dh2048.pem
server-bridge
push "dhcp-option DNS 8.8.8.8"
;bind to the second internet link's IP address
local 192.168.2.100

Enable Multi-Path TCP (MPTCP)

MPTCP is an extension of TCP that allows multiple paths to be used simultaneously. This feature is crucial for combining the bandwidth of two internet connections. You will need to enable MPTCP on your server.

To enable MPTCP, add the following kernel parameters to your system configuration:

- Edit the sysctl file `/etc/sysctl.conf` and add: 

net.mptcp.enabled=1
net.mptcp.mptcp_enabled=1

- Apply the changes: 

sysctl -p

- Confirm MPTCP is enabled with: 

sysctl net.mptcp.enabled

Configure Load Balancing Between the OpenVPN Instances

Use a load balancer or routing policy to combine the traffic across the two OpenVPN server processes. This will ensure that the incoming and outgoing VPN traffic is distributed evenly between both internet links.

A simple example using iproute2 for load balancing: 

ip route add default via 192.168.1.1 table 1
ip route add default via 192.168.2.1 table 2
ip rule add from 192.168.1.100 table 1
ip rule add from 192.168.2.100 table 2

In this example, packets from the first link (192.168.1.100) will be routed through `table 1`, and packets from the second link (192.168.2.100) will be routed through `table 2`. You can further optimize the load balancing rules based on your use case.

Verify and Test the Setup

Once you have set up the configuration files and load balancing, it's time to test the system.

- Start the OpenVPN server processes with: 

openvpn --config /etc/openvpn/server1.conf
openvpn --config /etc/openvpn/server2.conf

- Ensure that both VPN connections are active and routing traffic correctly. - You can verify the bandwidth aggregation by running tests like `iperf` or checking the speed of the outgoing and incoming VPN traffic.

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