I'm writing a C# remote control for my media player. It runs on my Android phone.
I have a client app listening for TCP connections on my computer which, one a connection has been established, processes commands (Volume up, volume down, ...). I've tested that part using telnet 127.0.0.1 on my computer, and it works great.
Things are trickier when it comes to connecting from my phone, since it's not on the same network (I don't have Wi-Fi, only wired connections), so I'm not sure how to proceed. Basically I want to connect to a computer that's behind a router.
Should I rather host the TCP server on my phone, and have the PC connect to it? Take IRC as an example: although I'm behind a router, I can connect to servers outside, without port forwarding.
Or if hosting the server on my computer is fine, how do I connect to it?
I don't understand everything to this yet, so feel free to correct me if I got something wrong.
It would be more logical to keep the PC hosting the server, and configure your router to forward connections to your PC. You have two options:
Establish a DMZ: all incoming connections on the router will be forwarded to one PC only. This is easiest when you only have 1 PC on the network that needs to accept connections.
Configure port forwarding: you can instruct the router to forward connections incoming on port X to the IP Y on port Z. This way, multiple PC's can listing for connections (using different ports on the router). It is also a bit more secure.
How to set these up depends on your router, but most routers just accept connections on their port 80 and offer an easy web-interface. If you give your router brand, we can link you to the manual.
Things are trickier when it comes to connecting from my phone, since
it's not on the same network (I don't have Wi-Fi, only wired
connections), so I'm not sure how to proceed. Basically I want to
connect to a computer that's behind a router.
What you want to achieve is possible, but you need to learn about NAT traversal and hole punching.
Most often, devices behind a NAT/Router have a private IP address only valid on the LAN. Remote devices can't guess it. This private address is translated into a public IP address by the NAT when the device wants to communicate with the WAN.
The easy solution is you can give a public IP address to the device behind the NAT. In this case, remote devices on the WAN will easily be able to reach it, because its address is public.
Related
I have an android client which has to communicate through socket to a c# based pc server. The question is, if the pc server is behind a router which somwhow does not seem to support port forwarding through upnp, or even through configuration, it simply cant get connection.
These routers are some kind of free wifi zones prepared for free by some kind of companies, so I can't have any access to it's configs. The upnp or configuring my router both works fine, but I dont really know what to do about these routers.
It's common for a home router to only allow established connections by default. Even with a VPN tunnel or CHAP Callback, you would still need configuration on both ends imho.
I like to connect to a TCP server that run in a machine that is connected to the LAN in my home network. This LAN can be connected to internet via either following methods.
1. Through a router which has a wireless or wired WAN connection
2. Through a router which uses a mobile broadband connection, for example a router that accept a USB modem to connect to internet.
I know in the first case, we can use port forwarding.
In the second case, I believe telcos use PPP protocol and port forwarding does not work.
In addition, even in the first case, if ISP does not give a static IP, then we need to use DNS mapping service to map a fixed URL to the allocated dynamic IP and we need to configure router to go and register the dynamic ip at the start up.
My question is, are there any other better methods that can be used in this situation? I am wondering how chat applications connect to each other? I hope they maintain a TCP connection between two devices, without a central relay server?
I have a question about network connections among computers.
I've made some applications where messages pass through the Internet (via sockets) to make a connection between two devices. However, a strong condition is that two devices must be connected to the same network.
Can anyone give me a trick how to create a communication using sockets between two computers even if they are connected to different netwkorks?
Thank you in advance.
Here is a great tutorial on how to use sockets and general networking
(in java) http://www.thenewboston.org/watch.php?cat=25&number=38
In order to communicate between two diffrent networks over the internet, you will need to do something called port forwarding. What that does is that when your public IP of your network receives a packet with a spesific port number. The router knows where to send that packet to which local IP.
If you dont port forward and receive some data. The router doesent know where to send the packet. Therefore it discards it, which means others wont be able to connect to you.
You will only need to port forward the network with your server (using the example i linked). How you do that is by logging in to your router, and say that a port which the server uses gets forwarded to the IP of the PC hosting the server.
On the other network (client) you will need to change the IP address of which the client shall connect to. That IP address needs to be your public IP of your server's network. You can find that by connecting to the server's network and go to: http://www.whatsmyip.org/ . Keep in mind that public IP addresses may change over time.
Hope this helped!
-Kad
I did not know where to ask this so here it is. This is more of a networking technology question, but any pointers will help.
Suppose, I want to connect to a machine behind multiple gateways. Say I want to connect to my home computer from my office computer. My home computer is behind my ISP's gateway and then behind my wireless router at home. Let's say I know the IP's for all of them. (global IP for my ISP's gateway, local IP for my wireless router within my ISP's n/w and my home machine's local IP within my home). How do I initiate a TCP connection with my home computer ? The standard berkeley socket program only takes one IP and so I can only connect to machines that have global IPs.
Is there a solution ? Am I correct about the berkeley sockets ?
Thanks.
It is entirely possible, with the cooperation of the ISP. The fact that the ISP is giving private addresses should urge you to move to another.
The concept you're after is called DNAT or Port Forwarding.
Let's say you decide on accessing port 1234 on a PC. The address of the PC is Local2. The address of the wireless router (in the network with the ISP) is Local1.
The wireless router must do the translation Local1:X -> Local2:1234
The ISP router must do the translation Public:1234 -> Local1:X
The X means any port can be used.
You only need to know the destination IP address to connect from an application, the gateway address is for the forwarding (routing) of packets which is handled by the OS network stack. However, if the destination is behind NAT, you'll only know the public IP address of the destination's NAT device. Even in this scenario, all you have would be an IP address and you don't really know if there is NAT going on.
If your destination is fixed, you could set up port forwarding on the NAT device (if you control it). Otherwise, you just realized that NAT is pure evil.
In your situation, it appears you want to connect to your home computer. If your wireless device has a public IP address, you can setup port forwarding on that to forward all incoming traffic on a port to a port on your home computer.
I want to connect to a system which is behind a router. I know the public address of the router as well as the private ip (fixed always) of the system. How do i establish socket connection with the private ip?
This is why some people say that they are behind a "firewall", when they are behind a router. The Evil Viruses Of The Internet are not able to exploit any software on a computer behind a router (provided that the router admin didn't configure it in the funny way, for example by enabling DMZ).
You still have some options:
Talk to the router admin and make him forward a port for You
Take the router out and put Your "target" computer where Your router was, or enable DMZ (this only makes sense if there was only one computer behind the router). Warrning: install a firewall on the target computer first!
Turn the socket 180 degrees. Make the computer behind a router establish the connection to the server that has a public IP address
Use something like UPnP, if Your router supports it
Get a dedicated IP address for Your computer and configure router to switch all traffic to this IP address to Your computer (this is similar to DMZ, but would work if You have more than one computer behind the router). Warrning: install a firewall on the target computer first!
Use NAT traversal. There is a very good article on the subject here. Simplified version is that client establishes connection to some remote server. The server can see the opened port number on the client's router and this port is assigned to the client's machine, so it (or some another computer sharing this information) may establish connection to that port and reach the client's application. Warrning: this doesn't work with all routers. Some routers just won't let this happen.
The simplest thing is probably to forward the port from the system you want to connect to through the router.
This is more a question of configuration of the router as opposed to your actual program. If the router isn't configured to forward traffic to the private system, there's no way to force it to connect you - rather, the private system would have to open the connection on its own.
Strictly speaking, the answer to your question is "you can't". You can however enable DNAT (Destination Network Address Translation) on your router. You connect to a certain port on the router, and it forwards the connection to the internal ip. The internal ip (and port) are configured in the router settings and are not known by the connecting client.