You don’t have a valid submit button in your html code.
Remove your link and use an input type “submit” or a button 
Replace :
<div class="form-group">
    <a href="https://stackoverflow.com/questions/29392261/<?= base_url() ?>ipmpab/addIpMpabDb/" class="btn btn-success">
        <span class="glyphicon glyphicon-plus"></span> add
    </a>
</div>
With :
<div class="form-group">
    <button type="submit" class="btn btn-success">
        <span class="glyphicon glyphicon-plus"></span>add 
    </button>
</div>   
… For exemple
Then add the action attribute to the form :
<form method="post" action="<?= site_url('ipmpab/addIpMpabDb'); ?>">
0
solved input data codeigniter always 0 on database