I'm developing a game that can be played with computer or versus other players. The GUI is Swing but irrelevant for the matter. My question is : how do I connect with other players in a network?
I am familiar with terms like client / server, sockets etc, and i can write a basic client/server program, but it can only be run from ONE computer. I don't know how to connect to this network from a computer, say, half way across the country.
You are probably setting behind a router which hides your local IP address from the rest of the world (look for NAT for more info on this). Basically, the world only sees your YOUR_ROUTER_IP, your router takes care of carrying all IP packets from the outside world to you and vice versa. You will need to change your router settings so that your computer/server gets the router ip address. This way you can access your server application from anywhere in the world by using simple socket operations.
I hope this helps.
I like to use Kryonet for network connections, it works very well and has really good documentation.
You indicated you know how to use client and server sockets, so I'll just throw out there that you ought to try connecting with "real" ip address instead of localhost (127.0.0.1). Take two machines on your local network, get the IP address of the "server" machine and use that address to connect from the client.
This will work all the way around the world, except for the fact that you are likely behind some Network Address Translation (NAT) firewalls and will likely need to "open" or "forward" the ports you need. If you need more information on NAT, google and serverfault will be pretty helpful.
If your client and server is located on the same machine, then you can use loopback address(ie 127.0.0.1), in LAN you can do with private ip addresses
Private ip address for LAN
CLASS A - 10.x.x.x
CLASS B - 172.16.0.0 - 172.31.255.255
CLASS C - 192.168.0.0 - 192.168.255.255
you can use this for LAN environment
For connecting someone over the internet, you will need Public ip addresses.
Address apart from the private ip in every range are public address.
Now if you have a server which is having a static ip then it wont be a problem for the client to access it anywhere from the world over internet.
But if its over a LAN , and accessing the internet from a gateway, then there will be a NAT, then you will need to set the inbound and outbound traffic rules at the gateway, for letting the client access the server.
Related
I found some basic examples online about sending messages between computers in Java. However i realized that i only used local ip addresses so i could only send messages to a pc connected in the same network. I rewrote most of the code to make a slightly better version but if i wanted to send a message to a computer in a different network, connected to the internet, would switching the local ip with the receiving computer's public ip address in the code do the trick?
Yes it should work, however it's common place to connect to the Internet via a modem, which in term is the device holding the public IP. Some NAT and likely port forwarding would be needed at the endpoint.
To give a short answer : yes, as long as the receiving computer has a public address and there is no proxies blocking requests.
I'm working on a server-client project. I hosted server on Google app engine so there is no problem with IP there, all the clients can connect to the server easily. Yet the problem occurs when I try to connect to a client, which is quite complex because I don't have static IP for the clients. Can anyone suggest me a good way for server-client coomucication in this case, without requiring that clients must have static IP address?
Thank you very much.
Well, obviously the client should register itself with the server and update it's IP when it changes.
There is, for example, a program which does exactly that and then publishes the IP with a DNS.
But you should be aware that the IPv4 address space is not that big and a lot of internet clients do not own an IP (and work thru the ISP's NAT). If you have clients that do not own an IP then you might want to stick to the usual Pull: the clients should periodically issue a request to the server to check if there are new messages for them. With a Keep-Alive connection and an efficient server implementation the price of such checks might actually be low, although that kind of communication might not work very well with the GAE pricing.
Is there any possible way to differentiate online IP Address from Local/Other Machine IP on LAN in Java?
I am working on a application, there is a need to identify the Local IP/LAN IP and Online IP address input by user.
Thanks in advance.
As far as I am aware, there is no way to do this based solely on the IP (and that is not specific to Java, but based on the way networks work).
If you have additional information, however, you may be able to do this. There are three networks of IP addresses that are not used on the internet. Those are:
10.0.0.0/8
172.16.0.0/12
192.168.0.0/16
If you know the LAN IP addresses will be from specific ranges (including the network the host is in on which your application is runnning), you can differentiate; however - and do not try this at home kids since it will give you headaches - if you use IP addresses in your LAN that are also used on the internet, you will not only have address conflicts, but also trouble to distinguish between online and LAN IPs.
Something else though; if your users try to "connect" via the internet, but are behind a NAT, your application will only see the source of their traffic as the public IP of the gateway doing the NAT for your users. So, for example, if two of your users are somewhere in a LAN with IPs from 10.0.1.0/24, but their gateway has a public IP of 123.123.123.123, your application will see BOTH users as having the IP 123.123.123.123
You might have to come up with a different way of authentication if you intend to use this in a way similar to VPN, or you have to know all the public IPs of all gateways of all of your users who are behind NATs.
A note on terminology, as Marcelo pointed out: afaik, "online" and "offline" are not terms usually used with IPs. We rather speak of "public" (the ones seen on the internet) and "private" IPs (those within your own network noone on the internet can see).
You can get the external IP using some API such as http://automation.whatismyip.com/n09230945.asp. If you can reach that API and get the IP, you are "online" - i.e., connected to the internet. If you can't, you are "offline" (unless the host is down, etc).
If you need the local host, you can use
InetAddress thisIp =InetAddress.getLocalHost();
System.out.println("IP:"+thisIp.getHostAddress())
Please clarify what you consider an "offline IP address", as I've never heard of such concept before.
I created a small chat program, that works flawlessly when client & server are run on the same computer (and probably network, too).
However, as soon as I try to connect to another computer over the internet, the socket connection simply times out.
Is this because of firewalls / routers, etc?
And how can I connect a ServerSocket & Socket over the internet?
However, as soon as I try to connect to another computer over the internet, the socket connection simply times out. Is this because of firewalls / routers, etc?
Yes, most likely. You're running into the NAT problem: essentially, the same externally visible IP address maps to many internally visible endpoints, and external endpoint doesn't know which internal endpoint to give your socket request to.
The easiest way around this is to have both your clients connect to a third party which both of them can see, and then have the third party mediate the communication. This is how most instant-messaging protocols work, for example.
If you have no way to control a third-party entity like that, an alternative to directly connect two clients is to have both clients open up an agreed-upon port, and then map communications on that port to their own internal endpoint. This provides the missing link that the externally visible endpoint (e.g. your home router) needs to deliver the communication to its intended destination.
If your server is behind a NAT router box (and most home computers are, especially if you use WiFi), then it won't be reachable from the outside unless you set up your router to port forward to that server.
What's the IP of your server computer? If it's 192.168.x.x or 10.x.x.x, then it's a non-routable address and can't be reached from outside.
Assuming with running on the same computer you mean that you tell the client the server is at 127.0.0.1 / localhost, it shouldn't be a problem in your code but because of firewalls or routers. If your server is behind a router performing masquerading (i.e., the server doesn't have a public but private IP address like 192.168.x.y for instance), you have to configure the router to pass a connection from the internet to the computer running the server.
Another reason why it doesn't work might be the way you bind your server to the interface. If you specify 127.0.0.1 there, the server will only listen for requests coming from the same system. If you don't specify an address, it will listen on all interfaces.
Edit Your comment indicates that you indeed have the NAT problem like others said. Configuring your router accordingly is probably the easiest solution.
First, test to see if it really works on a LAN; it sounds like you're just assuming it does.
If it works on your local network, perhaps it's failing because the server lacks a public IP, and is running behind a NAT'ing router.
Java Socket Program did not work for WAN
I have written a TCP IP socket program which works fine in my LAN.
One of my friend is at bangalore He ran the server and I ran the
client with the host name of my friend's IP. In this case my
socket program did not work.
You said that your program is attempting to connect to host 192.168.1.107 port 46216.
192 prefix specifies it is a class C address and is private. Making your program connect to that will force it to remain on the local network searching for that node. You will need to find the IP address of your router (you can use http://whatismyip.org/ to find this out). Then go into your router settings and forward port 46216 to 192.168.1.107 (your node), or even better, your MAC address which is not subject to change (in case your router is running DHCP).
on a side note, it isn't good to hardcode IP addresses. Simply use a textfield to avoid having to redistribute the client when your IP is changed, as it is likely you have a dynamic IP from your ISP.
Your friend running the server is most likely behind either a firewall or NAT. Make sure you are using the external IP address and if necessary port forwarding the packets to the correct IP.
The IP address you gave seems to be a local address, rather than a public internet address. If you are looking for 192.x.x.x, you will not make it out to "the internet", but will be confined behind your router.
WhatIsMyIP is a good way of getting a public IP address, and THAT is the address you should use in your connection. Also, be sure to forward any ports that will be used by your program, because otherwise your router will likely filter the traffic and still create an issue.
You could use an implementation of STUNT or other NAT Traversal protocol.
The ip of computer on thih u deployed your server program is not in your reach.
192.x.x.x ip means (class C) it is for local subnet.
You need to have change your ip address of your net-adapter so that your router could route it through internet.