code: def add_firewall_rule(self, direction, action, src=None, dst=None):
          
          value = [action]
  
          if src:
              value.extend((src, dst))
  
          self._set_aliased('router-firewall-%s' % direction.lower(), ' '.join(value), multi=True)
  
          return self
docs: Adds a firewall rule to the router.
  
          The TunTap router includes a very simple firewall for governing vassal's traffic.
          The first matching rule stops the chain, if no rule applies, the policy is "allow".
  
          :param str|unicode direction: Direction:
  
              * in
              * out
  
          :param str|unicode action: Action:
  
              * allow
              * deny
  
          :param str|unicode src: Source/mask.
  
          :param str|unicode dst: Destination/mask