Universal ip4/ip6
<?php
function encode_ip ($ip)
{
    $d = explode('.', $ip);
    if (count($d) == 4) return sprintf('%02x%02x%02x%02x', $d[0], $d[1], $d[2], $d[3]);
 
    $d = explode(':', preg_replace('/(^:)|(:$)/', '', $ip));
    $res = '';
    foreach ($d as $x)
        $res .= sprintf('%0'. ($x == '' ? (9 - count($d)) * 4 : 4) .'s', $x);
    return $res;
}
function decode_ip($int_ip)
{
    function hexhex($value) { return dechex(hexdec($value)); };
 
    if (strlen($int_ip) == 32) {
        $int_ip = substr(chunk_split($int_ip, 4, ':'), 0, 39);
        $int_ip = ':'. implode(':', array_map("hexhex", explode(':',$int_ip))) .':';
        preg_match_all("/(:0)+/", $int_ip, $zeros);
        if (count($zeros[0]) > 0) {
            $match = '';
            foreach($zeros[0] as $zero)
                if (strlen($zero) > strlen($match))
                    $match = $zero;
            $int_ip = preg_replace('/'. $match .'/', ':', $int_ip, 1);
        }
        return preg_replace('/(^:([^:]))|(([^:]):$)/', '$2$4', $int_ip);
    }
    $hexipbang = explode('.', chunk_split($int_ip, 2, '.'));
    return hexdec($hexipbang[0]). '.' . hexdec($hexipbang[1]) . '.' . hexdec($hexipbang[2]) . '.' . hexdec($hexipbang[3]);
}
?>
DB:
`user_ip` varchar(32) DEFAULT NULL