code: def update_ip_rule(self, ip, mac):
          
  
          rule_no = self._find_rule_no(mac)
          chain = self._find_chain_name(mac)
          if not rule_no or not chain:
              LOG.error('Failed to update ip rule for %(ip)s %(mac)s',
                        {'ip': ip, 'mac': mac})
              return
  
          update_cmd = ['iptables', '-R', '%s' % chain, '%s' % rule_no,
                        '-s', '%s/32' % ip, '-m', 'mac', '--mac-source',
                        '%s' % mac, '-j', 'RETURN']
          LOG.debug('Execute command: %s', update_cmd)
          dsl.execute(update_cmd, self._root_helper, log_output=False)
docs: Update a rule associated with given ip and mac.