* @return {@link Inet4Address} of embedded IPv4 in 6to4 address
   * @throws IllegalArgumentException if the argument is not a valid IPv6 6to4 address
   */
  public static Inet4Address get6to4IPv4Address(Inet6Address ip) {
    checkArgument(is6to4Address(ip), "Address '%s' is not a 6to4 address.", toAddrString(ip));

    return getInet4Address(Arrays.copyOfRange(ip.getAddress(), 2, 6));
  }

  /**

      assertThrows(
          "IllegalArgumentException expected for '" + non6to4Address + "'",
          IllegalArgumentException.class,
          () -> InetAddresses.get6to4IPv4Address((Inet6Address) ip));
    }

    String valid6to4Address = "2002:0102:0304::1";
    String ipv4Str = "1.2.3.4";

    InetAddress ipv4 = InetAddresses.forString(ipv4Str);