If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

But it has to look, swim, and quack like a duck. If it only does one or two, it might be something else entirely.

Almost two years ago I opened a ticket on GitHub because I couldn’t (and still can’t) install packages via pip on an IPv6-only host with an IPv6-only resolver. Fastly is used as a CDN, and the authoritative DNS servers involved simply don’t have AAAA records. It’s just a matter of switching to a different set of DNS servers.

But that’s not what this article is about. Yes, I have an IPv6 problem. You may also have a problem involving IPv6. Are they the same problem? Probably not.

In my case, I can’t connect because of a name-resolution issue. That’s completely different from:

  • performance issues caused by broken IPv6 connectivity at your provider,
  • certificate warnings caused by other configuration problems, or
  • anything else that only seems IPv6-related.

Before adding a comment, please read the ticket you’re replying to and check whether your issue is actually related. Similar symptoms don’t always mean the same cause.