I recently changed from an ADSL 10 MB to a GPON 40 MB and since then I'm having a bad headache.

My old ISP (ADSL) gave me always a valid public IPv4. Sometimes it changed but there was no problem since I used dynamic dns to reassign my hostname and access my home Open VPN installed in a Raspberry Pi. That was sweet.

But now, my actual ISP (GPON) uses something I never heard of: my public IP is this and according to their technical support, this same IPv4 address is used by more than one customer.

They installed a "Zhone ZNID-GPON-2426A-EU: S3.1.229" as the "router" for the fiber connection at my home. I tried to create DMZ and Port Forward (Remap) rules and they didn't worked so far...

Then... they told me that this public IPv4 address encapsulates (or sort of) my IPv6. They already enabled IPv6 with Prefix Delegation and IPv6 DHCP Server in the "router" (I really don't know if it is because it have a lot of functions). I can access my Raspberry Pi from outside with its IPv6 address (and tested VPN and SSH port in IPv6 online scanner page with positive results) but no no IPv4 access is possible (no Port Forward, no DMZ).

Since the place I work does not support IPv6 (just IPv4) is there something I can do to access my Home VPN through IPv4? It is possible using 6in4?

  • I have a service which is aiming to help in that kind of situation. It supports HTTP, HTTPS, and SMTP. If you are willing to apply a small patch to the client, it can also do SSH.
    – kasperd
    Jul 19 '15 at 7:44
  • You mention that you primarily want to use VPN. The service I mentioned above is not tested with any VPN protocols. But you are welcome to ping me on chat if you want to give it a try. Then we can find out if it is possible to get that working.
    – kasperd
    Jul 19 '15 at 8:01

Yeah, though most of the methods for doing it are janky as heck.

You're using Carrier Grade Nat for IPv4 and properish IPv6. To access IPv6 from IPv4 you need to set up a tunnel to a system that supports IPv4.

The jankiest way to do this is to use Teredo/Miredo. It's available on Windows and doesn't need much configuration but in my experience its horribly unreliable.

If you want to do it better use a tunnel.

I used to use gogo6/freenet for it, but there's other providers with variable levels of ease of use. You will need root/admin access and depending on your tunnel protocol possibly open ports.

If you don't mind spending a small amount of money, a cheap VPS that supports both would likely do many of the things your raspi do, and work pretty well as an intermediate. SSH into it, and ssh from there to the rpi, and you're cooking with gas.

  • 1
    The reliability of Teredo will depend on the ISP he is using at home. If that ISP has deployed Teredo relays with sufficient capacity, it will be reliable. If that ISP have not deployed any Teredo relays and instead forward the traffic to public third party relays, it will be unreliable. If Teredo sometimes works but is very unreliable, he need to contact the ISP he is using at home since they can make it reliable, if they want to.
    – kasperd
    Jul 19 '15 at 7:57
  • Well, my ISP was terrible about that - now I have native ipv6 ;p
    – Journeyman Geek
    Jul 19 '15 at 8:12
  • Maybe my comment wasn't clear enough. If one end of the connection is using native IPv6 and the other end of the connection is using Teredo, then the ISP providing native IPv6 decides how reliable the connection will be.
    – kasperd
    Jul 19 '15 at 8:16
  • @kasperd Thank you for your advice regarding VPS. I'm planning to use a Digital Ocean VPS to use VPN access. However you said that Teredo/Miredo are unreliable by your expericence. What do you mean? It is unsecure or have to many failures?
    – adamitj
    Jul 19 '15 at 17:31
  • @adamitj The answer to why Teredo is unreliable and what can be done about it is too long for a comment. If it hasn't been asked before it would be very suitable as a separate question. The answer in your case is however going to be, that if you use Teredo at work and want to connect directly to your home, then reliability will fully depend on Teredo relays deployed by your ISP at home, and they might not have any Teredo relays at all.
    – kasperd
    Jul 19 '15 at 18:35

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