NAT Traversal

As I briefly mentioned in my previous post, the next release will have some NAT Traversal (abbreviated NAT-T) technology built-in.

The only visible impact this will have on your experience, is that OCTGN now uses IPv6. So instead of the familiar IPv4 addresses (, you’ll see some longer numbers separated by colons:


The green address is a special one, which should be able to do NAT-T. So even if you can’t serve today, you should be able to with that one.

Here’s a quick FAQ for you – what you should really know:

I think that my computer/modem/ISP only supports IPv4, not IPv6. Does that mean that I can’t play anymore?
Windows provides 6-to-4 translation. That means that even if your network only supports IPv4, Windows will provide a ‘fake’ IPv6 for you and do some dirty work to make it work over IPv4. So you will be able to play!

What’s the deal with the other non-green IP addresses?
The green IP is a tunnel called ‘Teredo’. It’s the technology, which enables NAT-T. The other IP addresses are ‘regular’ network interfaces.
If you aren’t behind a NAT (i.e. if you can host games today), you don’t need to use a Teredo tunnel. You can simply use a white IP.

Does that mean that everyone is now able to host?
Unfortunately no. Firewalls can still block incoming connections, it is possible to disable Teredo if your network administrator really wants to, and a few NAT configurations can’t be passed through by Teredo.
But hopefully those are now exceptions rather than the rule.

How well does this thing work?
Honestly, I don’t know! I am not behind a NAT myself, so please post a comment after the next upgrade! Let me know if your are NAT’ed or not, what your OS is, and if you can host or not!
Teredo is enabled by default on Windows Vista and 7. It also works on Windows XP SP2 (or SP1 with Advanced Networking Pack), but Teredo may be disabled (you wouldn’t see any green IP). In that case, you can try to run these commands on a prompt:
1. Make sure IPv6 is activated:
netsh interface ipv6 install
2. Activate Teredo:
netsh interface ipv6 set teredo client
Again, I don’t have Win XP anymore, so please let me know if these commands are required or not!

I’m a geek! Tell me how can you traverse NAT?
A good starting point with basic explanations is reading what wikipedia has to say about IPv4, IPv6, 6-to-4, and Teredo. You’ll find plenty of links starting there.

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12 Comments on “NAT Traversal”

  1. Mauro Says:

    I know it’s an OT, but can you suggest me how to build a new game definition (o8g) and core set (o8s) for OCTGN 2? What is the best tool to use?

  2. jods Says:

    You should ask in the forums, it’s a much better place for that:

  3. Kurt Says:

    Looking forward to this. Any estimate on when this will be available?

  4. jods Says:

    Next week. I have tested this today and everything seems to work fine.

  5. Thronner Says:

    Hey Jods, there’s a problem with the IPGlobalProperties.GetUnicastAddresses method, I’ve already run the netsh interface ipv6 install and the
    netsh interface ipv6 set teredo client on cmd and it doesnt help in this method, I always get this exception:

  6. Thronner Says:

    Btw, I have windows xp home edition, .net 4 installed and nothing else I see as important

  7. jods Says:

    I am so glad you built from SVN and discovered that problem! I don’t have an XP box myself, so this platform is seldom tested.

    This would be a major problem as it makes OCTGN unusable on XP. I’ll have to look into it and it may delay the next update!

    Can you check the stacktrace and tell me which instruction is throwing the exception? The yellow highlight includes .GetIPGlobalProperties, .GetUnicastAddresses, .IsIPv6Teredo.
    [EDIT: quick follow-up: the official documentation states that all these methods are available on WinXP SP3. So I wonder: is is another method that throws? Is the documentation wrong? Don’t you have SP3?]

    I’ll double check the documentation, but from what I read in blogs this should work in XP SP2 SP3 (which SP have you?). Of course, the error message clearly says otherwise.

    BTW: how many of you are using XP? Vista/7? (Maybe I should grab statistics inside OCTGN… but that would probably be evil.)

  8. brian Says:

    did you take out IPv4 out? no one in my group can now connect to anyone, and all of our IPv6 connections show up red

  9. brian Says:

    If i run a “Netsh int ipv6 show Teredo” It’s state=OFFLINE…

    unless i turn on Windows Firewall (vista ult) then it shows State=Dorment and when i do an IPCONFIG /ALL i then resolve a ipv6 address on my teredo adapter.

    also now i resolve an ipv6 address in OCTGN.

    hope this info helps.

    • fantsu Says:

      Thank you brian, that helped me a lot, I have XP pro with SP2 and it does work now. 😀

      Just run:

  10. DEMIGOD Says:

    i cant connect even though i tried typing those netsh in command prompt im using window xp service pack 3 hope you can give some idea to work with it

    • jods Says:

      Sorry, I’m really out of ideas. Everything known so far is written in the forum thread.

      IPv4 support will be back this week-end, so wait for it and forget about IPv6 if it doesn’t work on your computer.

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