[johncolanduoni]

You can do this quite easily on all the major OSes by opening a single dual-stack socket. On most Linux distributions that is the default, and then mapped addresses will work fine if the machine has a v4 address or a 464XLAT configuration. This has been the case for about 20 years.

[hackthemack]

Opening a dual stack ipv4 and ipv6 does allow the service to accept both ipv4 and ipv6 connections. But I do not think that is what zadikian is getting at?

It does not address the network level identity and reachability. There is no default, globally routable mapping where owning a ipv4 automatically gives you an equivalent identity in ipv6 that others can reach without translation infrastructure. The transition mechanisms are not uniform or canonical, and that increases complexity.

6to4 was an attempt at that kind of embedding and I do not think it succeeded?

The original specification of ipv6 did not directly address a translation mechanism? It seemed to rely on, well, everyone will go dual stack and we will shut down the old ipv4 stack. I think it should have addressed that in the beginning and provided the one canonical way of doing it, perhaps with guides on timelines to get the ISP and backbone providers to get on board.

[johncolanduoni]

I’m not clear on who is supposed to do the translating that isn’t doing it today, or why the mapped IPv4 addresses don’t qualify. Virtually all ISPs either give you an IPv4 address or do the translation for you, and the software you write doesn’t have to care exactly how it’s set up for the most part (there’s some subtlety about stuff like MTUs, but if you’re just doing unencapsulated TCP it usually doesn’t matter). It can just use whatever comes back from DNS (including using the official mapped addresses if only an IPv4 record exists) and expect the network stack to figure it out.

None of this stuff works perfectly, but it’s powering almost every mobile internet connection in the world so I don’t understand what is missing.

[hackthemack]

You wrote "I don't understand what is missing"

ipv6 was standardized in 1995 6to4 was standardized in 2001

6to4 is not used in any meaningful way today.

What was missing was ipv6 should have had 6to4 (but better) in it, in 1995.

Now, I could go on about what is wrong with 6to4, but every new topic is just another surface area for ipv6 proponents to launch another question (I sometimes suspect in bad faith).

[zadikian]

If you look at the reasons GitHub for instance doesn't support ipv6, it's a different set of problems from what cell carriers had to deal with.

[zadikian]

Yeah we're talking about the same thing. So my v4 is 70.94.201.31. My ISP didn't also give me 2002:70.94.201.31 or whatever.

[throw0101a]

> My ISP didn't also give me 2002:70.94.201.31 or whatever.

Traffic to 2002:70.94.201.31/48 is tunnelled via 70.94.201.31 with-in an IPv4 packet (encapsulation):

* https://en.wikipedia.org/wiki/6to4

[zadikian]

I mentioned 6to4 in the original comment. It doesn't fulfill this use case, it still relies on v4 packets.

[tardedmeme]

They're allowed to do that if they want to. Most find there's no practical reason to ensure the addresses are related. It wouldn't help them support v6 faster.

[zadikian]

Do they own such an address, as in, a packet sent by someone on another ISP to that address will actually reach my ISP's router over v6? Not talking about translations that use v4. If they do, I've never seen them actually give it to me.

[tardedmeme]

Yes, they can just put your 32-bit IPv4 address after their 32-bit prefix, and that gives you a /64 as is standard. If they want to. But what's the advantage?