Browsing SEN I noticed that Lanth and I (but only at work) are the only 2 people on SEN that show an IP address that literally reads "unknown". This is obviously not possible or we would never receive an answer from SEN.

So what's going on? Is it an IPv6 address that SENs forum software can't interpret (but SENs server can)?

My work uses Ipv6, so I'd say yes.

My network is set up for IPv6 (test-ipv6.com does give a passing grade and I can indeed open IPv6 sites), and I don't get an IPv6 address from a DNS lookup for staredit.net or www.staredit.net, so I'd say that probably isn't what is going on.

I think you got Nude's hypothesis a little backwards, he seemed to say:


Rather than:

The point about staredit.net not having an IPv6 address is that you would still need to access it from an IPv4 address and it would know nothing about the existence of your IPv6 address. You cannot directly access IPv4 addresses from IPv6 addresses; you need to also have an IPv4 address to send it through, whether it is directly assigned, on a proxy used for your web access, or located at a tunnel endpoint.

Of course, if it is being accessed through a proxy that is accessed by using its IPv6 address and if the forum software is looking at an extra HTTP header value sent by the proxy to indicate the address of the computer accessing the proxy, then it could possibly be receiving an IPv6 address that way. However, considering that local IPv4 addresses aren't useful for identifying the computer or connection, it is unlikely it would be looking at such an HTTP header value sent by the proxy even if one existed.

So IPv4 and IPv6 are basically separate nets that can only communicate via a proxy or something that translates the addresses? Furthermore this architecture would be transparent for the IPv4 net?

Anyways, when I visit IP checker websites I always get the same IPv4 address, and no IPv6 address. So it's apparently not that. And why can't SEN register the IP when other sites can?

Pretty much. Hosts (ie, computers, tablets, phones, etc) can be dual-stack, that is they support both IPv4 and IPv6 natively, or they can use some sort of tunnelling service, so that an IPv4 host can talk to an ISP that only supports IPv6 and still communicate with the rest of the IPv4 internet through their IPv6 ISP. I presume you can also tunnel IPv6 over an IPv4 network as well - since about 2006 or so people have gotten serious about IPv6 and are creating lots of different migration technologies to solve every conceivable need. Then there are methods of mapping IPv4 addresses into IPv6 addresses, and again I presume there would be proxies and other methods to map IPv6 back to IPv4 as well.

Windows Vista and later actually default to using IPv6 within a LAN were possible.

Beats me. There's nothing really special about my IP addresses (apart from having IPv6 at work), as far as I know. I do access SEN from home and from work, but I expect other people do that as well, so it seems strange that it'd only affect me and you.