<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script type="text/javascript">

function IPv4Validate(myfield, e)
{
	if (!e)
		var e = window.event
	if (e.keyCode)
		code = e.keyCode;
	else if (e.which)
		code = e.which;

	var character = String.fromCharCode(code);

	// if they pressed esc... remove focus from field...
	if (code==27)
	{
		this.blur();
		return false;
	}

	if ( e.ctrlKey
		|| code == 8
		|| code == 9
		|| code == 36
		|| code == 37
		|| code == 38
		|| (code == 39 && (code != 39 || character != "'") )
		|| code == 40)
		return false;

	var integerOnly  = /[0-9\.]/g;
	if ( ! character.match(integerOnly))
		return false;

	var str = myfield.value + character;
	var pattern = /\d{1,3}\.?/g;

	var result = str.match(pattern);

	if ( ! result )
		return false;
	if ( result.length > 4 )
		return false;

	for (var i = 0; i < result.length; i++ )
	{
		var pp = /\d{1,3}\./g;
		if ( (i != result.length - 1) && ! result[i].match(pp) )
			return false;
		else if ( i == 3 )
		{
			pp = /\./g;
			if ( result[3].match(pp) )
				return false;
		}

		var str = result[i];
		str.replace(".", "");
		if ( parseInt(str) > 255 )
			return false;
	}

	return true;
}
</script>
</head>

<body>
<p><label for="inputIPv4">IPv4 address only</label> <input type="text" id="inputIPv4" onkeypress="return IPv4Validate(this, event);" /></p>
</body>
</html>