function checkIP2(sIPAddress)
{
    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 = sIPAddress.match(exp);
    var ErrMsg="你輸入的是一個非法的IP地址段！\nIP段為：:xxx.xxx.xxx.xxx（xxx為0-255)！"    
    var Msg="你輸入的是一個合法的IP地址段！"    
    if(reg==null)
    {
        alert(ErrMsg);
    }
    else
    {
        alert(reg);
    }
}（出處：Viphot）