python server socket closes immediately

Question

I have a simple server-client combo running on 2 computers in 2 different networks. The server (a Raspberry) has a TCP tunnel running.

Now running on the code on localhost is fine, on 2 different machines with correct IP and port (I can ping the server via telnet and establish connection via ssh using the same IP and port), I just get the following on the client side AND NOTHING ELSE:

Received SSH-2.0-OpenSSH_7.9p1 Raspbian-10+deb10u2

I should instead receive: Received b'Hello, world'

On the serverside I receive no message at all.

What do I need to run it in 2 different networks? Below the source codes.

server.py:

#!/usr/bin/env python3

import socket

HOST = ''  # Standard loopback interface address (localhost)
PORT = 65432  # Port to listen on (non-privileged ports are > 1023)

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.bind((HOST, PORT))
    s.listen()
    conn, addr = s.accept()
    with conn:
        print("Connected by", addr)
        while True:
            data = conn.recv(1024)
            if not data:
                break
            conn.sendall(data)

client.py:

#!/usr/bin/env python3

import socket

HOST = 'xxx.xxx.xxx.xxx'  # The server's hostname or GLOBAL IP address
PORT = 12345 # The port used by the server, not actually 12345

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.connect((HOST, PORT))
    s.sendall(b"Hello, world")
    data = s.recv(1024)

print("Received", repr(data))

Answer 1

等待大神答复