code: def request_port_forward(self, address, port, handler=None):
          
          if not self.active:
              raise SSHException("SSH session not active")
          port = int(port)
          response = self.global_request(
              "tcpip-forward", (address, port), wait=True
          )
          if response is None:
              raise SSHException("TCP forwarding request denied")
          if port == 0:
              port = response.get_int()
          if handler is None:
  
              def default_handler(channel, src_addr, dest_addr_port):
                  # src_addr, src_port = src_addr_port
                  # dest_addr, dest_port = dest_addr_port
                  self._queue_incoming_channel(channel)
  
              handler = default_handler
          self._tcp_handler = handler
          return port
docs: Ask the server to forward TCP connections from a listening port on
          the server, across this SSH session.
  
          If a handler is given, that handler is called from a different thread
          whenever a forwarded connection arrives.  The handler parameters are::
  
              handler(
                  channel,
                  (origin_addr, origin_port),
                  (server_addr, server_port),
              )
  
          where ``server_addr`` and ``server_port`` are the address and port that
          the server was listening on.
  
          If no handler is set, the default behavior is to send new incoming
          forwarded connections into the accept queue, to be picked up via
          `accept`.
  
          :param str address: the address to bind when forwarding
          :param int port:
              the port to forward, or 0 to ask the server to allocate any port
          :param callable handler:
              optional handler for incoming forwarded connections, of the form
              ``func(Channel, (str, int), (str, int))``.
  
          :return: the port number (`int`) allocated by the server
  
          :raises:
              `.SSHException` -- if the server refused the TCP forward request