新手一个问题请大家帮忙看看，关于onblur的问题函数老是调用不进去

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title></head><body>
<script type="text/javascript">
//校验IP地址格式 
function test()
{
   //alert("haha");
    window.alert(document.form3.ipaddress.value);
}function checkip()
{
var scount=0; 
var ip = document.form3.ipaddress.value; 
var iplength = ip.length; 
var Letters = "1234567890.";
//window.alert(iplength); 
//window.alert(document.form3.ipaddress.value)；

//window.alert(CheckChar);
for (i=0; i < document.form3.ipaddress.value.length; i++) 
        { 
      var CheckChar = document.form3.ipaddress.value.charAt(i); 
window.alert(CheckChar);
    if (Letters.indexOf(CheckChar) == -1) 
        { 
            alert ("IP地址格式不对!!，只能输入数字和“.”,格式为XXX.XXX.XXX.XXX 例如：192.168.0.1"); 
            document.form3.ipaddress.value=""; 
           document.form3.ipaddress.focus(); 
           return false; 
       } 
    } 
}
</script><table width="97%" height="120%" valign="top">
  <tr>
    <td width="45%" height="100%" valign="top">
<fieldset>
      <legend>IP配置</legend>
      <p>
      <fieldset>
       <legend>IP设置方式</legend>
       <form id="form1" name="form1" method="post" action="">
         <p>
  <label>
<input type="radio" name="RadioGroup1" value="单选" />
固定IP</label>
  <br />
  <label>
<input type="radio" name="RadioGroup1" value="单选" />
PPPOE连接</label>
  <br />
</p>
        </form>
  </fieldset>
      <fieldset>
<legend>PPPOE</legend>
   <form id="form2" name="form2" method="post" action="">
     <table width="100%">
                        <tr>
                          <td width="23%"><div align="right">用户名</div></td>
                          <td width="77%"><input type="text" name="textfield" /></td>
                        </tr>
                        <tr>
                          <td><div align="right">密码</div></td>
                          <td><input type="text" name="textfield2" /></td>
                        </tr>
                      </table>

</form>
  </fieldset>
  <fieldset>
<legend>IP地址</legend>
  <form id="form3" name="form3" method="post" action="">
<table width="100%">
                      <tr>
                        <td width="37%"><div align="right">IP地址</div></td>
                        <td width="63%"><input type="text" name="ipaddress" id="ipaddress" onblur="checkip()" /></td>
                      </tr>
                      <tr>
                        <td><div align="right">子网掩码</div></td>
                        <td><input type="text" name="mask" /></td>
                      </tr>
                      <tr>
                        <td><div align="right">网关</div></td>
                        <td><input type="text" name="gate" /></td>
                      </tr>
                      <tr>
                        <td><div align="right">域名服务器一</div></td>
                        <td><input type="text" name="dns1" /></td>
                      </tr>
                      <tr>
                        <td><div align="right">域名服务器二</div></td>
                        <td><input type="text" name="dns2" /></td>
                      </tr>
                    </table>
  </form>
  </fieldset>
</p>
  <input type="submit" name="Submit" value="提交" onclick="checkip()"/>
  </fieldset>
</td>
    
<td width="45%" valign="top">
  <p>
  <fieldset>
  <legend>连接控制中心</legend>
  <p>
  <fieldset>
<legend>控制中心IP设置</legend>
<form id="form4" name="form4" method="post" action="">
  <table width="100%">
<tr>
  <td width="37%"><div align="right">控制中心IP地址</div></td>
  <td width="63%"><input type="text" name="textfield4" /></td>
</tr>
<tr>
  <td><div align="right">控制中心端口</div></td>
  <td><input type="text" name="textfield42" /></td>
</tr>
  </table>

</form>
<form id="form5" name="form5" method="post" action="">
</form>
  </fieldset>
    </p>
            <form id="form6" name="form6" method="post" action="">
              <input type="submit" name="Submit3" value="连接测试" />
      </form>
      <p>
        <input type="submit" name="Submit2" value="提交" />
      </p>
      </fieldset>
  </p>
  <p>&nbsp;</p>
  <p>&nbsp;</p>
    <p>&nbsp;</p>
    <p>&nbsp;</p>
    <p>&nbsp;</p>
    <p>&nbsp;</p>
    <p>&nbsp;</p></td>
  </tr>
</table>
</body></html>onblur里面的老