Hello,

I'm trying to setup a VPN(using OpenVPN) between 2 machines:
Computer A: a Raspberry Pi used as a lowcost surveillance system running Raspbian connected to internet via a 3G link,behind CGN and IPv4 only.
Computer B: my home laptop running Archlinux connected via a fiberlink, also behind CGN but is IPv6 capable.

My first trial was to setup the openvpn server on A but 3G networks don't allow incoming connections...

The only option left is to run the openvpn server on B but I can get only an IPv6 public address from the second ISP.

I found similar issues on this forum with suggestions to use a tunnel broker.There was a free hosted vpn called Hamachi, but the free part is gone.

The 'surveillance system' is just an Ip cam streaming at 4FPS grandma's house in a remote village, so the live stream will be used rarely on motion triggered events.I also need SSH and FTP access to the remote machine.

So how do I get a link between A and B?
Is there a way to make the setup more simple ?
What other options are there ?

Thanks in advance !

I'm still using hamachi for free; however there is a 5 client limit per network. Additionally I'm still using version 2.1.0.86 as it does not give me installation/service-start issues. Also i recommend using the LogMeIn dashboard for creating your networks ("My Networks"). If you create them via commandline, you risk losing your creator account.

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If I'm reading the question correctly, you're basically saying that there is no way to connect directly from A to B (since B has an IPv6 public address), or from B to A (since A blocks incoming connections), using any protocol. Is that correct?

Then I think the only option is a 3rd party IPv4 server that can act as a middle man. I don't see why you need a full hosted VPN server, just basic ssh access should do, and then you can have A autonomously set up reverse ssh tunnels to the 3rd party server on the necessary ports. Is there a reason you need (or think you need) a full VPN? That seems beyond overkill to me.

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I try to avoid Hamachi because all traffic goes through their servers and when I last used this service(7-8 years ago) it had low connection speed. There are still serveral things I need to try, but if everything else fails then I will give hamachi another try.

Not quite, B is IPv6 capable, but right now it has an IPv4 address. I tried to setup dynamic dns(http://www.dynu.com) for it and I had the option to ping my IP after setup. The ping failed and still fails from sites such as http://ping.eu/ping/, so I assumed that the vpn client(on A) won't be able to reach the server(on B). My assuption is wrong because I talked to my ISP and they said that they don't filter any ports except SMTP and recomended me to use their own dyndns service. I tried it on port 80 with httpd (hosting a test webpage) and it works ! I wanted to adopt IPv6 for the sake of 'internet health' ...

Well, besides the IP cam I want to control other devices such as a relay board for irrigation or read a temperature/humidity sensor, all of these having a simple web interface. I may give access to this interface to a selected few so multiple clients is a plus.

I'm not very good at ssh and only used it to install software on the Pi, so the openvpn aproach seemed more simple and general for using client-server applications that require different open ports.

cross-platform Hamachi alternatives:

n2n - a Layer Two Peer-to-Peer VPN
SoftEther VPN Project
tinc vpn
freelan (no redhat, et al?)
NeoRouter Free (as opposed to the Mesh and Pro versions)

i have no experience with any of them, but tried to maintain a list for when i was ready to move-on.