There's a way to make a MySQL with XAMPP go online to connect by Mobile Data (Android app) or PC app without beeing on the same local area connection?
This are the specs of the PC where XAMPP is running:
16GB RAM
i7-8700
SSD - 512GB
Integrated GPU
100MB Internet Connection (Optical Fiber)
What im tying to do is connect to the DB without beeing on the same connection as the PC where XAMPP is on execution,something like open the Android app on California meanwhile the PC is on Baja California
The problem is that your PC is most likely sitting behind a router. The router maps multiple private IP addresses to one public IP address. How does it do that? It uses NAT. In very basic terms, when a device D1 (say with private ip 192.168.1.10), sits behind a router and wants to communicate with a public device D2, it sends a request. The request goes to the router. The router adds the public IP address and an arbitrary port (e.g. 12345) to the packet. The router keeps a table with all ports linked with the private devices (e.g. 192.168.1.10 -> 12345, ...). Then it sends the packet to D2 using D2's public IP address. D2 sends a response back to the router public IP. The router forwards the packet to the private device using the port number and the table, in this case the device is D1.
So, you can't directly communicate with a device sitting behind a router from outside the router. However, you can use port forwarding. You can tell the router to always map a specific port to a specific private IP (your PC's IP). Then, you make the other deivce (your Android app) communicate with it using that port.
In summary, if we have two devices, A and B, and A is behind a router. If A wants to initiate a connection with B, then:
if B is behind the same router, then they can use their private IP addresses.
if B is not behind any router, then A can communicate with it using B's public IP address, as demonstrated above.
If B is behind a different router, then there must be some kind of port forwarding.
Related
I'm programming a client-server app, my client being an android phone, my server being my laptop.
So my issue is that this one line of code:
Socket connectionToServerSocket = new Socket(hostName, portNumber);
works perfectly fine when my cellular phone connects to the Internet with my home wifi connection, and simply times out when connected through 3G (cellular provider) eg it blocks for a while then throws a timeout exception.
The funky thing is,that I can see (using OS Monitor) that some apps are connected through very common ports, for example port #80, but switching portNumber (as well as the port that the server is listening to) to 80 doesn't help (eg it still times out), and I've tried many different ports-same result.
DNS works fine (eg it translates the logical String which I gave hostName to the correct IP) but it doesn't send the server anything...
I'm lost,what could be the reason? How can I check and resolve it?
I've run into this issue as well doing a similar application.
Your laptop and phone can connect to each other while on the same network because they share a IP address lookup through your router.
When the device is connected to the WIFI, it's request get passed through the router to check for IP addresses, it will find your laptops IP and save a request to a DNS because it can find the laptops IP already. The laptop works the same way, it finds the Ip address of the client through the router as well.
However, when your phone is on 3G, it has no way of knowing exactly where your laptop's IP address is. That's why it times out: it goes from your router to your nearest DNS (where it tries to resolve the correct IP Address), if it cannot find a domain or IP that matches it will fail.
Some steps to fix this . . .
Depending on your router you can set up port forwarding for your laptop's IP. This means incoming requests to your router can be piped to your laptop's server implementation.
Then go to any site like this http://touch.whatsmyip.org/ on your laptop to get your laptops IP. Save this to add to your clients Socket set up.
For debugging until your laptop server is visible for DNS lookup, go into your client code and add this.
Socket debugSocket = new Socket("the.laptop.ip", 80);
Some warnings:
Depending on your Router, your ip may change during restarts
With port-forwarding any browser with your ip, ex) 178.12.434.01 can log onto your laptops personal server
Future Changes:
Once a dedicated server is up and running, registered with a domain you can change the above ip parameter to "your.domain.com", and behind the scenes the actual IP address to your server will be found via DNS lookup.
the reason for that is that the server in your laptop is closed to external network by default, what you need to do is something called port forwarding
*take note: port forwarding put your server in a cyber security risk, make sure you make the right adjustments to keep your server safe.
case 1: It is working when your laptop and your phone is connected to wifi right ?
Try this once
case 2 :
connect your phone to 3G.
enable hotspot on phone.
connect your laptop to your phone's hotspot.
check the IP of your laptop if it is changed replace that in Socket object. Socket connectionToServerSocket = new Socket(newIP, portNumber);
Run your project.
Just try this once you will get what i am trying to say.
You are getting the timeout exception because your server that is
having the service is not reachable from the external network.
Hope this will help :)
I am trying to make an application which consist of a Java UDP client and a PHP UDP server. I am thinking about binding the server with the client over internet, because the client may not have real/public ip address. Though the server is a web application itself which will open a listener on the public address over some port. The task of the client is to communicate (send/receive) data over UDP.
Communicating parts:
Client: Windows/Linux OS connected to Internet (Java application)
Server: Windows IIS Server, with a real ip and domain (PHP web application)
This will depend on the firewalling/NAT-ing policy at a given client site, but the usual setup is to allow UDP out to the server and then allow corresponding reply packets back in, based on source and destination addresses and port numbers.
It would be a problem if you were to try and create a server behind your router.
Your router will replace the client's local ip address with the public ip address of your router at the moment that you send something to the server. The router will internally keep a translation table. This translation table is consulted when the server sends a reply to retrieve the original IP adress where the request originated and then the reply is simply forwarded to that IP address. As such it seems as if you are using the ip# that is allocated for you usually using DHCP by your router. But this local ip# is never seen on the internet only on your local lan.
Because the translation table is built by you trying to send to a server, you cannot easily setup a server behind your router. Simply because your router will not have an entry in its translation table to route the request coming from the internet to your server. This is called NAT/PAT. Because the translation table keeps track of ip adressen and ports.
All IP addresses are real. But people talk about a public IP# and a local IP#. The public IP# is the one that is used on the internet where the local ip# is the one that you use on your local LAN.
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
server code:
String ip = request.getRemoteAddr()
if(ip='127.0.0.1')
System.out.print("hello");
Now I am accessing that remote site from my machine, so obvious my IP address should be like 192.*.*.*.
How can I cheat the server(IP spoofing) so server always prints "hello" for my request?
New answer to edited question:
You can't in Java. If need to pretend that the request is coming from 127.0.0.1 (the server itself), so you'll need to hack into the network stack of your operating system.
Old answer:
The IP Address your client uses to connect to the server depends on the network interface it uses and the kind of network attached to this network interface.
Example:
If your client is a laptop it most likely has only one network interface. This network interface uses 192.168.1.10 as its IP address (e.g., assigned from the DHCP on your router) as its internal IP address. Your router might also be connected to the internet, with an IP, say 20.20.20.20, which it shares with connected devices via NAT.
If you use this to connect to your server which is on your local network, the client's IP address that the server sees will be 192.168.1.10; if you connect to your server which is not on your local network but somewhere on the internet, your client's IP (that the server sees) will be 20.20.20.20
So you cannot make your client pretend to use 127.0.0.1 (if server and client are running on the same machine, your client will most likely have 127.0.0.1). Of course there are techniques like IP spoofing where you pretend to have a different IP than you actually have, but that's totally different issue.
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.