Comment by Dagger2

5 days ago

You'd think it would be long enough for people to realize that v6 is backwards compatible! Yet no, here we are, constantly dealing with people making the same damn claim that it isn't every single time a v6 story is posted.

v6 is about as backwards compatible with v4 as it's possible to be. If you have a way to make it more backwards compatible then I'd love to hear it, but when I ask this all I ever get are things that don't work, or things that v6 already does.

5 comments

Dagger2

Reply
bradley13  5 days ago

No, it's not. If I have an ipv6 network, an ipv4 address is invalid. It's that simple.

  • Dagger2  4 days ago

    It's not that simple at all. For one thing, having a v6 network doesn't mean you can't have a v4 network. You can run v4 in exactly the same way you currently do, with exactly the same software, and it'll work no worse than it already does.

    But for another, the v4 space is available as a subset of the v6 space:

      $ ping 64:ff9b::8.8.8.8
  PING 64:ff9b::8.8.8.8(64:ff9b::808:808) 56 data bytes
  64 bytes from 64:ff9b::808:808: icmp_seq=1 ttl=113 time=9.82 ms

    That's from a machine on a network with no v4, and it works fine. I can reach v4-only sites from it too. I could even do this using v4 addresses if I wanted, but if I showed you the output from that you'd just claim I was using v4.

    • bradley13  4 days ago

      The point of backwards compatibility would be to allow IPv4 devices to work on an IPv6 network. Not to run a parallel stack.

      127.0.0.1 needed to be a valid IPv6 address, along with all the others. Pick a particular prefix, say 0...* and any address with that would be extended to 128 bits. That would have been backwards compatible.

      1 reply →

  • jcgl  4 days ago

    No, it’s not—IPv6 networks are totally capable of providing IPv4 as a service. SIIT-DC, 464XLAT, MAP-T