Simple PHP IPv6 detection script (http://wp.me/pnbL6-6a)

v6.php

<?php
header('Content-type: application/json');

if ( array_key_exists('addr', $_GET) )
    $ip = $_GET['addr'];
else
    $ip = $_SERVER['REMOTE_ADDR'];

$v6 = preg_match("/^[0-9a-f]{1,4}:([0-9a-f]{0,4}:){1,6}[0-9a-f]{1,4}$/", $ip);
$v4 = preg_match("/^([0-9]{1,3}\.){3}[0-9]{1,3}$/", $ip);

if ( $v6 != 0 )
    $type = "IPv6";
elseif ( $v4 != 0 )
    $type = "IPv4";
else
    $type = "unknown";

echo json_encode(array("ip" => $ip, "type" => $type));
?>

v6_ajax.js

$(function() {
  $.get("http://pub.jbhannah.net/v6.php", function(d) {
    if( d.type != "unknown" )
      $("#remote_ip").html("Connected via " + d.type + " from " + d.ip);
  }, "json");
});