I have set up a client and a server using sockets in python where my client sends data to the server, servers performs an operation, then returns some data to the client. Originally both the client and server were to have the same port number (9999). My issue currently is that I have to change the port of the server to 19999, and when I try to run, it does not work. The client is able to send data if its port is also changed to 19999, but it does not work if client is 9999 and server is 19999, which is what I need. New to networking systems so would appreciate any useful links to information or advice.
pic of client (left) and server (right)
Normally, clients will use an ephemeral port for its local port, and connect to the server port. Your client code is attempting to connect to port 9999, which is not the server port, which explains why it is not working. You need to connect to port 19999, since that is the port the server is listening on.
Using an unbound socket causes the client to choose an ephemeral port for its local address when making a connection. If you want the client to bind to a specific port, use bind before you call connect.
# bind locally to 9999
local_addr = (host, 9999)
s.bind(local_addr)
# connect to 19999
remote_addr = (host, 19999)
s.connect(remote_addr)
Related
I created a multi-threaded client/server application that can send messages to each other at real time. Everything works perfectly, but I want to be able to send messages over the Internet. From what I understand, I need to do port forwarding to be able to make my server reachable for the clients. I then set up my port forwarding options by providing a port (9991) and then my Macbook Air's IP Address (192.168.0.1).
I then tried to connect to my server using my public server IP (let's say 197.132.20.222) and it didn't work. I then tried to see if the port forwarding worked by using this website: https://www.yougetsignal.com/tools/open-ports/ and I realized that the connection was closed. I also tried the command nc -vz 197.132.20.222 9991 while running my application and the connection is refused.
I'm using a JavaFX application, and for my server side I use a ServerSocket with port 9991. For the client side, I use a Socket and set the IP Address to my public router IP Address, and I tried to connect with another PC using mobile data to use a different network.
My firewall settings are turn off, so I really don't know what is blocking my application to connect to that port. Could it be my ISP is blocking connections? I just don't understand why my ports are blocked even with no firewalls enabled.
The Preamble
I start up my local SSH terminal at work behind a firewall, and connect to a remote server all the time without any problem.
The way Xdebug works, correct me if I'm wrong, is that it sends an "unsolicited" request to my network's port 9000. I actually initiated that action by sending the remote server an HTTP request through my browser with a POST/GET/COOKIE variable instructing xdebug to start up. But my network doesn't know that. All it knows is that it is getting a request on port 9000 from the internet. It doesn't know which computer in its private network to forward it to (without setting up port forwarding on the router), and can only ignore the request.
So if you can't do port forwarding, another option (and a much better one from what I can tell), is SSH tunneling. My computer sends the SSH request, the server responds. My router knows which computer in its network to route these responses to. Piggybacking on that SSH connection allows those "unsolicited" port 9000 requests from the remote server to get to me.
I think I understand that much.
I finally got tunneling to work, thanks to stackoverflow, but how it works is still fuzzy to me.
On the remote server, I tell Xdebug to connect to localhost (not to my ip via xdebug.remote_host=173.123.45.56, and not to xdebug.remote_connect_back=1 which also would end up at my IP) on port 9000. Connecting to localhost seems a bit weird, since I picture that as the server sending messages to its own IP address, as if it is sending messages into itself (but I think that connecting to localhost is probably fundamentally different than connecting to any other IP... I don't think the message gets routed out and back in to localhost).
On my computer at work, I open up an SSH connection on port 22, specifying a tunnel to/on port 9000, and remote port 9000. I've seen some explanations of the various settings here but still don't understand them. Some even seem to involve three machines. What seems to be happening though, is I'm connected as usual via port 22, but I've told the remote machine that I want to receive its port 9000 communications. I've specified "localhost" in my tunnel, and I suppose that might need to match the localhost in my xdebug.remote_host value. I wonder if I specified my IP address in both places (i.e. xdebug.remote_host=173.123.45.56 on the remote server, and same IP in my SSH terminal), would that work too?
So Xdebug on the remote server sends me a request to initiate a debug session. It comes through my port 22, but my SSH tunnel somehow makes it seem that it is coming in on port 9000. So my IDE that is listening on port 9000 receives the request and sends a response (also on 9000), which my SSH tunnel intercepts somehow and sends back to the remote server on port 22, where it is similarly spoofed into looking like port 9000 to xdebug.
The Crux
So what I'm really not clear on is, what exactly is the localhost in my SSH tunnel configuration referring to? Does it relate directly to the xdebug.remote_host=localhost value? Can I change them both to my IP address?
Are all of the remote server's outgoing communications on port 9000 being forwarded to me, or just some of them? E.g., if someone in Chattanooga initiates a debug session in their browser, will I receive Xdebug's response?
Are all of my outgoing communications on port 9000 being forwarded to that server? I.e. can I debug two applications on two different servers at the same time, with some of my port 9000 communications going one way and some the other, or would I need one port per local application? (I can use Google Chrome and Firefox browsers at the same time, both on port 80, for example.)
The tunnel consists of an SSHD listening to port 9000 (as well as 22) at your end and an SSHD listening to port 22 at the other end. When you connect your XDebug to your local 9000, the SSHDs intercommunicate and the remote SSHD connects to port 9000 at the remote. Thereafter your local port 9000 behaves identically to the remote port 9000: all data written to either end appears at the other end.
I have to make an app using C/PHP sockets on linux that sends data from one socket to other socket, like this.
I have server (server_hosted) hosted somewhere with an IP or domain name. It is running web application.
I have another server (unknown_server) running at my home (unknown IP).
Client send some information through web application hosted in server_hosted to another server running at my home (unknown IP).
I need a way to established a connection between server_hosted and unknown_server.
I was able to make connection between both using TCP socket. I made server_hosted as server listen to certain port says 8080 and unknown_server as client, which make open connection to server_hosted.
The problem comes when I have multiple unknown_server at my home. How can I made connection to same port? How many client can TCP/IP support?
Any ides how to make tunnel or connection between server_hosted and unknown_server.
Is possible to do with curl or socket any better ideas?
I need to accept only connections from particular client ip address at server side. Should not use acl. With help of socket strict bind at server side can i do?
Example:
client ip address: 1.1.1.1
server ip address: 1.1.1.2
At server side:
1. Open a socket
2. Bind socket with 1.1.1.1(client ip address) with port no.
Will i be allow to do the second step at server side? Any special options are there to do?
Please let me know.
Thanks,
Boobesh
You can only bind the server port to an ip address to specify the interface to use.
For example your server has two network interfaces, one connected to the internet and one to a configuration network. The webserver should maybe only listen on the internet interface and a management tool only listen on the configuration network.
For your purpose you can accept the connection, compare the ip address and if it is not in the list of allowed clients close the connection immediately (or after sending an error message).
The other solution would be to use a firewall that is configured to allow only connections from the specified clients to the server port.
I agree with the friend above, u can only manage the ip and port in you server, but not client. u should compare the coming socket with the one u store in your server.
I have a simple TCP socket client and server application. They are communicating using IP = localhost and port = 33367.
I'm using SocketSniff to examine my packets going through localhost. While sniffing the client app, I noticed that every time I'm sending a packet to the server in the same process, the "local port" is changing, while remote port is always 33367.
So, is it possible for the client apps to send their data through a fixed port (if so, how in C#?) or do they have to get assigned a different port each time?
You can bind the socket before calling connect.