Openvpn – How to force all traffic through VPN

openvpn

I have a openVPN set up on the server and I am using openVPN connect for my client. I have some internal websites that I need to access and some of them don't work. I want to make sure that when the traffic is going through the VPN and not though the normal internet connection. The gateway ip for my network is 192.168.0.1 and the gateway for openVPN is 10.8.0.1. I have done trace route and it shows that the websites that don't work access 192.168.0.1 and not 10.8.0.1. How would I force all of the traffic through the vpn? I am running windows 7 as the client and ubuntu 10.04 for the server.

Best Answer

From the OpenVPN HowTo Documentation

Implementation

Add the following directive to the server configuration file:

push "redirect-gateway def1"

If your VPN setup is over a wireless network, where all clients and the server are on the same wireless subnet, add the local flag:

push "redirect-gateway local def1"

Pushing the redirect-gateway option to clients will cause all IP network traffic originating on client machines to pass through the OpenVPN server. The server will need to be configured to deal with this traffic somehow, such as by NATing it to the internet, or routing it through the server site's HTTP proxy.

On Linux, you could use a command such as this to NAT the VPN client traffic to the internet:

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

This command assumes that the VPN subnet is 10.8.0.0/24 (taken from the server directive in the OpenVPN server configuration) and that the local ethernet interface is eth0.

When redirect-gateway is used, OpenVPN clients will route DNS queries through the VPN, and the VPN server will need handle them. This can be accomplished by pushing a DNS server address to connecting clients which will replace their normal DNS server settings during the time that the VPN is active. For example:

push "dhcp-option DNS 10.8.0.1" will configure Windows clients (or non-Windows clients with some extra server-side scripting) to use 10.8.0.1 as their DNS server. Any address which is reachable from clients may be used as the DNS server address.

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