I want to send a message from one computer (server) to another computer (client). Both the client and server are on an internal network with different IP addresses.
How do I send the message using the IP address without using the command prompt?
You need to look at socket programming.
Here is list of good tutorials that does what you are after:
How to use Sockets in C#
TCP/IP Chat
Simple TCP/IP Chat client/server
Creating a Mutli-User TCP Chat Application
The Microsoft link (the last one) is in VB.Net, but you can use the Code Convertor tool to help convert it to C#.
Also, there is the Lidgren Network library that is very easy to use.
You need to have a look at System.Net.Sockets namespace. What you're asking is very vague and it doesn't appear that you have investigated all that well. Sockets allow you to connect to other machines (and listen for incoming connections appropriately) and pass data between the two.
Related
I was wondering it it was possible to relay a socket object in either C# or Java? (Preferably C#)
I have lots of little programs i make and host them on my home pc, but my pc is behind a router, so i have to forward a port on my router every time i want to make a new application. So is there a way to send a tcp connection to another application on the same computer? for instance i get a connection in with the first line of text being RELAY::21005 which would then forward that port to localhost:21005 ?
Any help, tutorials, code snippets would be much appreciated. Thank you! :)
One problem you might face with your suggested solution (first line identifies target port) is that you'll have to change all of your client programs to send that first line. That's easy for programs you've written yourself but not so convenient if you want to connect to your PC's web server or ssh daemon etc. It's not impossible of course, but does make it hard.
I'd suggest your routing server listens on two ports - a control port and a "normal" port (I can't think of a better name at the moment). You would send control messages to the control port to indicate "until further notice redirect all incoming connections on the normal port to port nnnn". That avoids having to manipulate client protocols.
I don't know enough C# to provide advice about a C# solution, but in Java I'd simply do something like:
while (true) {
acceptConnectionOnNormalPort()
connectToTargetPort()
startThreadCopyingDataFromAcceptedPortToTargetPort()
startThreadCopyingDataFromTargetPortToAcceptedPort()
}
You'd not be able to scale that easily into thousands of connections...
K I take back my comment, check this out:
http://msdn.microsoft.com/en-us/library/aa395195.aspx
Using this requires the port sharing service to be up (it is disabled by default):
The Net.TCP Port Sharing Service is available on all operating systems
that support .NET Framework 3.0, but the service is not enabled by
default.
All of this is only useful to you if you are using WCF services tho.
The easiest approach IMO is to use ssh tunneling. As I wrote in my comment, there are lots of questions on SU that will show you how to do this.
But assuming that you want to program something ...
You'll need to create a client and a server. The client will have threads that call accept on whatever local ports you want to open. When a connection comes to a port, you create another thread that opens a connection to the server and continually sends data over the wire.
The server program listens on a single port, which you open in your firewall. It waits for connections on that port, and when it receives one it opens a connection to the specified local port. Then it shuffles bytes from one to the other.
The only trick is that you have to define a protocol for specifying the destination port in the client-server stream. Simplest approach is to write a two-byte integer at the start of the stream.
Yes, it is possible to relay a socket.
You can use TURN http://en.wikipedia.org/wiki/Traversal_Using_Relay_NAT
Some of TURN library/application:
pjnath
turnserver.sourceforge.net
What is the best way of reading, changing, and resending tcp communications?
For instance i have a server application that tells a master server it's alive sending a packet over TCP on port 3209. It sends out "I'm alive, my ip is xxx.xxx.xxx.xxx and I have currently 3 clients connected to me." the master server then responds, "Hello xxx.xxx.xxx.xxx i see you there."
Whats the best way of MITM of the server sending its packet to the master server? I would like to be able to change "i'm alive," to something like, "I'm changed," or even "currently 3 clients connected" to "currently 0 clients connected"
Any ideas appreciated, thank you.
There's no need to send out that kind of message.
First of all, TCP is connection oriented, so as long as you have a connection you'll be alive.
You can check if you're still connected by using the TCPClient.Connected property.
Secondly, TCP runs over IP so in the IP header you can find the sender IP (is in the socket properties) so no need to send the IP neither.
You can check the remote IP address by using TCPClient.Socket.RemoteEndPoint property.
Finally, the only thing you might be interested in telling is the "3 clients connected part" wich can be coded as a simple integer transmision. That is, a 4 bytes hearbeat.
Getting in the middle of the connection IS tricky and has nothing to do with communication protocols. And honestly it's a hell of a job, if there's a connection already present you'll have to find a way to make the client or the server drop it and then have the server reestablish it to your MIDM. More though, if the connection is made directly to an IP address you'll have to mess with the router tables somehow for the attact to be succesful, if it's not maybe DNS poisoning will work for you... anyway not an easy task.
Those are only ideas... it depends on the class of network, if you have physical access or not, if the client and the server trust each other (as in if they are your applications) and so on... I assume all this is ethical or educational at least... :)
Have a look at SharpPcap or any other packet capturing/injecting library.
In order to MITM, you'll have to force the client to think you're the server and the server to think you're the client. For that, you'll have to send ICMP packet to both machines as described here. Then, you will capture the packets, modify them and inject them to the network (with the correct MAC address).
Pick a different tool - this is too low level a kind of thing to attempt in C#. This kind of thing is achieved (on Vista and later) using the Windows Filtering Platform
I have a device connected to a host computer through cradle usb. Now, I'm just wondering if I could use C# sockets to communicate with the device (ie device sending data, host computer processing it then replying back to the device). How can I accomplish this? by that, what ip address etc etc.. do I have to change so that it would connect cause I have the sockets working on wireless. If not, then is there a way to connect to the device, open and read a file (a text document to be more specific) from the device to my host application.. any ideas?
Thanks! :)
Depending on your target device, when you connect via ActiveSync it likely makes a local RNDIS network connection between teh two devices. You can resolve "ppp_peer" as the partner's network name instead of trying to use a hard-coded IP address (IIRC the IP is different on XP than on Vista).
Be aware that it's not a full connection. TCP packets gets passed through, but things like ICMP do not.
Of course, this just gives you a socket connection, just like if you were to connect between two PCs. It's not going to allow you to do file system operations unless you have an app on the other side listening for commands. If you want that type of thing, Microsoft provides the Remote API (RAPI) interface (wrapped in managed code here)for a lot of basic commands, and it can be extended (with C) to do anything you'd like.
In my company we use small application called IPMsg, a messenger kind of tool to pass messages and file to other fellows in company, even it allows to multicast the message.
And also it lists the user name, host name and IP addresses of users.
How can it do that? There is no server present for message routing and when checked through netstat command in CMD it does not show any details like what protocol and port it is using to communicate.
There is source code also available on the same site which is in VC++. I didn't understand a line of code... (I'm a C# guy)
Can anyone explain me how it can do that?
One simple way would be to let the application listen on a certain network port, and when you start your instance of it, it tries to connect to that port on each computer on the same network. If that other computer has that port open, and answers correctly, then you have found another instance of the application.
IPMsg probably multicasts a request for all clients to report their user and host details.
A similar mechanism is used when Windows Explorer attempts to find other machines on a network. A good description of this type of multicasting discovery is described here.
IPMsg is a daemon which listens to incoming connections on a specific port which is the connection port. You can find out which port it used by using Wireshark.
Start wireshark, start listening on the interface where you have connected to LAN and then start sending any message, wireshark will show you the message on the screen with the port number also.
The application is a peer-to-peer software and doesn't require a central server software to route messages. it only has a small daemon which accepts incoming connections. This is the way Jabber Instant messaging protocol also works.
As you said it lists username, hostname and ip address of users, do you mean it pings the network and finds it? If yes, then it is actually possible to find the IP addresses of computers on the Local Network which requires you to know the subnet on which you are connected.
You can use ARP/ICMP Ping to know the hosts present on your network provided you enter the correct subnet information
Multicasting a message is also nothing special. It is a feature provided with all Networking Stacks.
If you want mutlicasting in .NET, it is allowed. Check this page on Code Project which gives a nice example
I've got some c# code that is mapping processes to ip addresses, I'm basically trying to write some software that will look at a process and give me the ip address so that I can write a monitor that will allow friends to find be in games.
When running my application though it detects that a game process has a UDP connection but I can't seem to get the ip address.
I've run a packetsniffer and 78.111.229.123:32000 shows up on the router/gateway but it's not showing in my application.
Any ideas to get me up and running?
How are you setting up the socket in the game application? Can you post an example of your socket setup code?
Are you using the wildcard address and port when creating the socket? I'm guessing that if your game application doesn't bind to a specific IP address and port explicitly that may be the source of your problem.
Another question: are you trying to detect the local IP address, remote IP address or both?
If you're trying to detect the remote IP address this may be impossible unless the game application is using what's known as connected UDP sockets. This is where the client application calls connect on the UDP socket to create an association between the local and remote sockets in the underlying OS. This has certain advantages and drawbacks as listed in the above link.
Edit
Take a look at this SO post: PID from socket number on Windows?
This pretty much confirms what I thought - unless the game is using connected UDP sockets then the only way you'll be able to get the remote address is via packet sniffing.
Start up the game and run netstat -ap UDP - if you see that there aren't any remote addresses listed then that would confirm the above suspicion.