// Server 1
<form action="http://192.168.1.6/post_cross_site.php" method="post">
    <input type="text" name="vstup" />
    <input type="submit" value="OK" />
</form>

// Server 2 - IP 192.168.1.6 a soubor post_cross_site.php
<?php
    echo $_POST['vstup'];
?>