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In-Reply-To: <db86fa40-991c-4977-9bff-668cb28fff93@Shaw.ca>
Date: Mon, 20 Nov 2023 23:36:29 -0800
Message-ID: <CAKwdsS8XKPOtnpTTHO5AqqL2F-FsxoifXM7FixG0HnO8pn+qGw@mail.gmail.com>
Subject: Re: Please support download setup-x86_64.exe on IPv6-only network
To: cygwin AT cygwin DOT com
From: Backwoods BC via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Backwoods BC <completely DOT and DOT totally DOT trash AT gmail DOT com>
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Sender: "Cygwin" <cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com>
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On Mon, Nov 20, 2023 at 9:36 PM Brian Inglis via Cygwin
<cygwin AT cygwin DOT com> wrote:
>
> On 2023-11-20 17:45, Lee via Cygwin wrote:
> > On Mon, Nov 20, 2023 at 7:13 PM Backwoods BC via Cygwin wrote:
> >>
> >> On Thu, Nov 16, 2023 at 12:41 PM Brian Inglis via Cygwin wrote:
> >>> The whole IP v4 internet is available as a compatibility subnet ::ffff:0:a.b.c.d
> >>> on IP v6, so there is no excuse for not supporting interconnection, as it will
> >>> be required until the last backbone routers drop IP v4 support.
> >>
> >> Just a small correction for the mail archives as this appears solved.
> >> The correct IPV6 address for the IPV4 address range is
> >> ::ffff:a.b.c.d  (no '0')
> >
> > If you're going for correcting the record, let's make it correct.
> > ::ffff:a.b.c.d is not a solution for IPv6 => IPv4 interconnection over
> > the Internet.
> >
> > from:  https://www.rfc-editor.org/rfc/rfc5156
> >
> > 2.2.  IPv4-Mapped Addresses
> >
> >     ::FFFF:0:0/96 are the IPv4-mapped addresses [RFC4291].  Addresses
> >     within this block should not appear on the public Internet.
>
> These internal addresses are used by dual stack hosts to allow clients or
> servers to handle connections to IPv4 hosts the same as IPv6 hosts.
>
> Whereas ::ffff:0:0:0/96 == ::ffff:0:a.b.c.d allows IPv6 only hosts without
> assigned IPv4 addresses to connect to IPv4 only hosts via SIIT see:
>
>         https://www.rfc-editor.org/rfc/rfc7915 Stateless IP/ICMP Translation.

Sorry I got this wrong. I admit to knowing only enough about IP v4 to
be dangerous (and design hardware for it), but I was relying on  this
site for IP v6 info:

<https://findipv6.com/ipv4-to-ipv6>

In my defence, I also saw this in RFC 4291:

2.5.5.2.  IPv4-Mapped IPv6 Address
   A second type of IPv6 address that holds an embedded IPv4 address is
   defined.  This address type is used to represent the addresses of
   IPv4 nodes as IPv6 addresses.  The format of the "IPv4-mapped IPv6
   address" is as follows:
   |                80 bits               | 16 |      32 bits        |
   +--------------------------------------+--------------------------+
   |0000..............................0000|FFFF|    IPv4 address     |
   +--------------------------------------+----+---------------------+

I hope you can see why I was confused and thought your comment was a
type. I apologize for doubting you.

There are far too many RFCs for someone who has never used IP v6 for
real. I'll just acknowledge that I don't know what I'm talking about
and slink back into the darkness.

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