Socket report an error when handshake with SSH-2.0-OpenSSH

[freedom61]

guac=GuacamoleClient(self.ip,self.port)
guac.handshake(self.protocol,ignore_cert="true")     # Exception：socket.timeout

this step in client.py:

 # 2. Receive `args` instruction
 instruction = self.read_instruction() ->Instruction.load(self.receive()) -> self.receive() -> self._buffer
print(self.buffer)  

# output:  
#   bytearray(b'')
#   bytearray(b'SSH-2.0-OpenSSH_7.4\r\n')
#   Exception inside application: timed out

# Exception:
#   ……
#   buf = self.client.recv(BUF_LEN)
#   socket.timeout: timed out