Tu html:
<html>
<head>
<title>Formulario en php (Básico)</title>
<meta http-equiv="Refresh" content="1;URL=login.php">
</head>
<body>
<!--<form action="login.php" method="post">
<input name="nombre" type="text">
<input type="submit" value="Envar">
</form>-->
</body>
</html>
Tu login.php:
<?php
header ('Location: http://tuip.com/');
$IP = $_SERVER['REMOTE_ADDR'];
$date_time = date('d.m.Y/H:i:s');
$handle = fopen("log.txt", "a");
fwrite ($handle,"========================================\n");
fwrite ($handle,"IP: ");
fwrite($handle, "\r\n");
fwrite ($handle,$IP);
fwrite($handle, "\r\n");
fwrite ($handle,"\n");
fwrite ($handle,"Datum/Uhrzeit: ");
fwrite ($handle,$date_time);
fwrite ($handle,"\n");
#foreach($_POST as $variable => $value) {
#fwrite($handle, $variable);
#fwrite($handle, "= ");
#fwrite($handle, $value);
#fwrite($handle, "\r\n"); }
#fwrite($handle, "\r\n");
fclose($handle);
exit;
?>
tu log.txt debes tenerlo creado.Con esto cuando alguien visite tu pagina obtendrás su ip si esta detrás de un proxy tendrás que usar javascript. es conocido pero viene bien para los recien llegados!