* @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));
  }

  /**

   * @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));
  }

  /**