button inside form should not submit form

in my form tag i have two buttons named SIGNIN and SIGNUP and form should be submit if SIGNIN button press. and if SIGNUP button press it should redirect to url given in anchor tag below but it always submitting the form. please help me.

<form action="controllers/user/vauth.php" method="post" role="form" class="userLogin" style="padding:20px;">
    <div class='alert alert-danger' id='errorLabel' style="display:none;"></div>
        <?php
        if(isset($_SESSION['error'])) {
        echo "<div class='alert alert-danger' id='errorLabel'>";
        foreach($_SESSION['error'] as $error) echo "<p><b>".$error."</b></p>";
        echo "</div>";
        unset($_SESSION['error']);
        }
        if(isset($_SESSION['message'])) {
        echo "<div class='alert alert-success'>".$_SESSION['message']."</div>";
        unset($_SESSION['message']);
        }
        ?>
        <div class="form-group">
        <label for="email">Email</label>
        <input type="text" name="vemail" id="vemail" class="form-control" placeholder="Enter Email" value="<?php if(isset($_SESSION['values'])) echo $_SESSION['values']['email']; ?>">
        </div>
        <div class="form-group">
        <label for="password">Password</label>
        <input type="password" name="vpassword" id="vpassword" class="form-control" placeholder="Enter Password">
        </div>
        <div class="form-group">
        <a href="user/vfpass.php">Forgot Password ?</a>
    </div>
    <button type="submit" class="btn btn-default" name="vsubmit">LOG IN</button><a href="../signup"><button class="btn btn-success" name="signup" style="float:right;">SIGN UP</button></a>
</form>