I'd like to get a tcp/ip connection working over the internet. I already have two classes, one tcpserver which handles requests and a tcpclient which connects, sends and receives data.
Until now I had it working perfectly on local networks. The usual 127.0.0.1 / localhost and my 192.168.xxx.xxx adresses are not giving any problems.
My question is, what do I have to do to make it work over the internet. As I might want to do some research involving a simple http/server I need this to work.
I doubt its my firewall but maybe its the ISP that blocks this type of connection. Anybody has an idea?
You need to open a port in the router that leads to the one that the server is listening on. You then connect to your public IP. This ip can be found on http://www.visaminip.se/
To provide a service over the internet you need a public IP address. 10.x.x.x and 192.168.x.x are private networks. 127.x.x.x is for the local machine only.
The client can connect to the public IP address of a sepecific port.
The server's modem/router/firewalls allows this port to be open and passes traffic to your server on that port.
Related
A common problem for a common project: I'm trying to run a ServerSocket Java program on my local PC and connect to it from an Android client. As others have experienced, things go smoothly when the client connects to the local address (eg. 192.168.xxx.xxx). If I try to connect through the internet, nothing happens:
Now, here are the things I tried:
Created inbound/outbound rules in Windows Firewall to allow traffic for the Server Port (3000)
Used the public IP in the client socket (IP obtained here)
Set up port forwarding on my router: inbound connection on port 3000 are redirected to the local IP of the server (eg. 192.1686.xxx.xxx again)
Check that the IP address of the server is listening to the port 3000 using "netstat -anp tcp".
Disabled any firewall on my router, just in case.
Still, there is no connection. Using this tool (https://www.canyouseeme.org/) I triedd checking that the port was visible (with the server app running of course), but nothing, all I get is a time out.
I'm out of options, I was hoping someone could show me what I'm missing.
Thanks.
(1) Does your PC where your server runs on have a public IP?
If you haven't applied for one and are running your code in a home or working environment, your computer only has a private IP. And considering the fact, your server and client connect well in the same LAN, the problem may be the IP.
(2)If you do have a public Ip, does your server listen on all IP address or just the LAN? Check the server bind IP is '0.0.0.0', and in ServerSocket constructor you can just set it to be null.
Alright, I have a java server setup using port 6567 and IP address 0.0.0.0 as to accept any connection. When I attempt to connect over my local network (192.168.1.15) I am able to connect just fine using the server. However when I switch to a non-local IP address (my routers public IP) I am unable to connect to it.
I have the router port forwarded and the proper rules in place on my firewall/etc. Is there any limitations on Java connecting in this fashion? I'm able to connect externally but not internally. Any thoughts on what might be causing this problem?
I'm starting to think it might be a router-specific problem, being that it could be rejecting the connection but I am unable to test that currently.
Turns out it was just the router itself that rejects internal connections using an external IP address. My personal fix was to just add a bit of testing code that automatically changes the IP if on a local machine to 127.0.0.1 rather then the external IP.
Worked flawlessly both on my own PC and having people connect externally once I set that up.
Hmm I'm not sure about it but maybe that will help.
Most probable, Your ServerSocket gets bound to a local IP address (e.g. 0.0.0.0) and ServerSocket binds to the port address there; and wouldn't respond to any requests coming from an IP address. Try new ServerSocket(4444, 50, InetAddress.getByAddress(new byte[] { YOU IP ADDRESS }).
or check again firewall
edit: Tell me how did you tried to connect from other IP than local?
I'm trying to write a simple chat program using TCP in java.
To connect to a server I need to know its IP address. I'm connected to a router in my network, that connects me to the Internet.
When I type local IP (assigned by router) it works pretty well between my two computers.
But when I typed public IP (I got it from google: "what is your ip"...) - it didn't work.
So I opened router's setup and make forwarding rule from my public IP and specific port to the local IP - and it worked.
--------- Question:
But how to do this without forwarding? I want to write a chat program. I can't tell my users: "just do the port forwarding" ;)
One opens my program and logs into central server, then writes there public IP. Some other user opens this server, download the file and gets first user's IP (or any other needed info).
But if first user didn't do the port forwarding, it won't work. How to make it work?
For this you will need to understand how something called NAT (network address translation) works. In simple terms the NAT is responsible for sending packets to the right computer on the internal network from the external.
Say for example you have computer A as a server on the internal network, and have computer B on the external. If you then try to connect to computer A from computer B, it will not work because NAT (your router) doesent know what computer to send that packet of data to, on the internal network.
Its diffrent when you want to connect to an external server. Lets say computer A (client) is on the external network, and computer B (server) is on the internal network with the router port forwarded to its IP-address. Then you will be able to connect to the server because NAT knows where to send the data packets.
So to keep all your users from port forwarding their routers:
Port forward your server on your internal network
Connect the clients on another network
For clients on the internal network; use the local IP of the server
Hope this helped!
-Kad
I am trying to set up a client/server model with android clients and a Java server.
The connection is over TCP.
I have all of my code working when the android device is on WIFI, however whenever I connect to a wireless network (eg 3g, 4g) the sockets refuse to connect.
I've been reading about NAT traversal but i'm not sure where to begin when implementing the necessary steps to allow the connection.
NOTE: my server has a static IP address
My guess is you have a network related problem. Assuming your server is behind a router, your server socket has to bind into its LAN IP (not directly binding the public internet IP). Then you need to setup port forwarding, firewall rules etc to ensure everyone on the internet can see your server (checking with online port open checker / telnet from another network is a good test)
I need to know the port i'm connected through the router , because I want to send it to an app, where an android can read it , and connect to my local app using the public ip of my router and the port. Can you help me? sorry for my bad english ;)
That's not how it works. A router performs NAT, which means it rewrites things in such a way that your application will get the packets intended for it even if the other end sends to your router's public IP, as long as you initiate a connection from inside the router.
If both ends are behind a NAT, you normally need to have a public-facing server which can mediate (description)