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I have installed OpenVPN on other VPS providers, and wanted to try out Google's. I like Googles price/performance, and especially because I can spin up the machines from my phone without logging in every time.

I've got it to the point where the client connects but can't get out to the internet.

I have opened up the firewall to the OpenVPN port.
I have enable IP forwarding on the virtual machine.
The client gets an IP, Gateway, DNS - all the right stuff - when connected.

I suspect I have to build a router and/or a route in order for the packets to get from the OpenVPN instance to the world. I have read the documentation very well, but I'm stuck - I'm not a network guru yet, still learning as I go. Through reading it looks like I can transform the network into what they call the "legacy" structure, but I'd like to be able to overcome this challenge and understand what's going on. I think it's because the network is broken into many different subnets; compared to just 1 network behind the firewall (ie Legacy).

Looking at a map in my mind, my OpenVPN is sending the data to it's subnet's Gateway, but from there I think the packets get dropped. I must need a route from the subnet gateway to the internet? Or even a full router between subnet and internet?

Like I said, I've used OpenVPN Virtual machines before, no problem. So I'm very confident that the issue lies within configuring the Google Cloud network.

Thanks for any tips.

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This fixed it:

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

Still not sure why I had to do it, maybe Google's Debian image is more locked-down than the standard Diebian instance.

No other Google Cloud network changes were needed.

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You need to checkout few things.

  1. Check whether you have following directive in /etc/sysctl.conf

    net.ipv4.ip_forward = 1

  2. Make sure firewall is forwarding the traffic received from clients on VPN interface

    #OpenVPN interface=tun0 iptables -A FORWARD -i tun0 -j ACCEPT

  3. Make sure you are masquerading the outgoing traffic

#WAN Interface on OpenVPN server is eth1 iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

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  • Thanks. net.ipv4.ip_forward=1, is uncommented by default. 2/3 Didn't make a difference. I added "~ # iptables -t nat -I POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE" and I THINK that made it work. Not sure why, but I've never had to do that with other Debian instances. – Greg Jan 21 '17 at 17:51

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