docs: def add(self, *args, **kargs):
          """Ex:
          add(dst="2001:db8:cafe:f000::/56")
          add(dst="2001:db8:cafe:f000::/56", gw="2001:db8:cafe::1")
          add(dst="2001:db8:cafe:f000::/64", gw="2001:db8:cafe::1", dev="eth0")
          """
          self.invalidate_cache()
          self.routes.append(self.make_route(*args, **kargs))