I'm trying to connect to my home network using OpenVPN. My router is behind the ISP's router so I'm having a double NAT problem (IP address on WAN port of my router is 10.x.x.x). ISP cannot provide me with public IP address directly as they don't have such an option so incoming connections are not possible.

My network configuration

I want to have access to the computers on my home network from the Internet.

What I think to do is to create ssh tunnel from my home server that runs OpenVPN server to my VPS that has public IP with something like

autossh -M 10984 -i /root/.ssh/pubkey -R 1194:localhost:1194 me@myvps

Then configure OpenVPN server/clients to use tcp over udp and connect to myvps:1194

So my questions are:

  1. Is there a better way to do this?
  2. What are the security/performance implications of such a solution?

What are the security/performance implications of such a solution?

You have two layers of encryption (SSH and OpenVPN), which might reduce performance – higher CPU usage and lower throughput, especially if one of your three involved devices doesn't have hardware crypto acceleration. (Even then, the SSH software rarely provides top performance.)

You also have three layers of nested TCP flow control (your regular traffic, inside the OpenVPN layer, inside the SSH layer). This might not work well.

Finally, throughput will be reduced by the tunnel overhead alone (SSH and OpenVPN packet headers eating into the available baseline 1500-byte MTU). Of course, one layer is unavoidable for a VPN, but doubling it might be noticeable.

direct: IPv4 <20> |                                                    | TCP <20> | application
vpn:    IPv4 <20> | UDP <8>                 | OpenVPN <41> | IPv4 <20> | TCP <20> | application
yours:  IPv4 <20> | TCP <20> | SSH <~20–40> | OpenVPN <41> | IPv4 <20> | TCP <20> | application

Is there a better way to do this?

As you already have a VPS, put the OpenVPN server there – and have your home system connect "out" to the VPS instead of the reverse. (Yes, the OpenVPN server will forward data between your 'home' and 'roaming' clients with no problems.)

This way you'll even be able to use UDP without any NAT-related problems, as long as you enable periodic ping in the client or otherwise maintain frequent traffic over the tunnel.

If you're using tun-mode VPN, the server just needs a kernel route for your LAN subnet through tun0, and then an OpenVPN iroute for the same subnet through the home VPN client's address. (With tap-mode VPN it's just a single kernel route combining both.)

  • Thanks for your answer! If I configure my home router (it has OpenVPN support) to connect to my VPS and then connect to the same VPS from outside my home network (eg using my phone with 3g) will I be able to access my home server by its dns name configured on the router (using dnsmasq) or I would need to do some additional routing? – hurlenko Jan 18 at 12:34

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