$config['sess_cookie_name']     = 'club_session';
$config['sess_expiration']          = time()+(60*60*24); //expire in one day
$config['sess_expire_on_close']    = FALSE;
$config['sess_encrypt_cookie']     = TRUE;
$config['sess_use_database']       = TRUE;
$config['sess_table_name']          = 'session';
$config['sess_match_ip']            = FALSE;
$config['sess_match_useragent']    = TRUE;
$config['sess_time_to_update']     = 300;

$session_data = array(
    'member_login_state' => TRUE,
    'memberID' => $memberID
);
$this->session->set_userdata($session_data); //set member

$session_data = array(
    'member_login_state' => '',
    'memberID' => ''
);
$this->session->unset_userdata($session_data); //unset member

public function member_is_logged_in()
{
    if ($this->session->userdata('member_login_state') == FALSE)
    {
        redirect('member'); //redirect to member login
    }
}

class Hub extends MY_Controller {

    function __construct()
    {
        parent::__construct();
        $this->member_is_logged_in(); // check member is logged in
    }

    //methods below.....
}

$config['sess_match_ip'] = TRUE;
$config['sess_match_useragent'] = FALSE;