<script language="javascript"> 
<!--
function checkIP() 
{ 
obj=document.check.ip.value      
var exp=/^(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])$/;
var reg = obj.match(exp); 
if(reg==null) 
{ 
alert("IP地址不合法!"); 
} 
else 
{ 
alert("IP地址合法!"); 
} 
} 
//-->
</script> 
<form name=check>
<input type=text id="ip"> 
<input type=button onclick="checkIP()" value="检测IP"> 
</form>