CODEWITHSUNDEEP
c#tcp
user2535425
user2535425

Reputation:

Initiating tcp connection from public IP to private machine on another network

I'm having difficulty finding help resources on this. I know how to use the TCPClient class to create a connection between one IP/Port/machine and another.

My doubt is how does that work when one machine wants to initiate a TCP connection to another machine where the destination machine is inside a different network. So the destination network may have hundreds of computers each with its own private ip and the network would have one public IP address. This would be using the TCPClient class or any other that is more appropriate.

I know we could use ports and then inside the network the port could be forwarded to the correct machine but I was looking for a solution like the one services like LogMeIn use. Basically I wanted to use port 80 always and then initiate the connection from the server to that particular machine or others on the same network when I needed.

I suppose, theoretically, I could create the connection first from inside that network, then on the server, save the details and close the connection and then in the near future, when I needed, I would re-open the connection.

So in my scenario, I would have many clients across multiple networks, each network might have multiple internal machines with a client installed. Then on the server I would initiate connection to these machines when needed. Within each network I would want to use port 80 for obvious reasons. The reason I want to initiate the connection from the server and not the client machines is simply to save resources, I couldn't cope with having opened connections until eventually I might need to communicate wit them.

Also, I have no control on the client networks besides them having my client installed.

Ideally, I wish to have c# info, possibly code and not network configuration.

Upvotes: 4

Views: 3322

Answers (6)

Andrew HON
Andrew HON

Reputation: 1

The topic is about NAT traversal. STUN is good choice to try to communicate with client behind NAT. But if STUN don't work,you can use RELAY service to help to pass the message between your server and remote client.RELAY service is a public service that everyone can reach it.

Upvotes: 0

videoguy
videoguy

Reputation: 1918

You need a third server that acts as proxy between your machine and target machine that is behind a firewall. That is how applications like LogMeIn work. You can do this using SSH tunnels.

Please check https://serverfault.com/questions/285616/how-to-allow-remote-connections-from-non-localhost-clients-with-ssh-remote-port

Upvotes: 0

Olivier
Olivier

Reputation: 5688

You may use SignalR, which has been developed for this kind of scenarios.

You must have a third party, though (a server which broadcasts messages from sender to other peers).

But the beauty of this technology is that it chooses the most appropriate way to push data to clients: Polling, long connections, sockets... etc.

This provides an abstraction layer which is quite comfortable.

It has been designed to interact with javascript clients, but may be used in full-C# clients as well.

Upvotes: 0

Hogan
Hogan

Reputation: 319

I had this requirement at a previous company. We installed our client/server software (C# based) on numerous different networks with a mix of public/private IPs. I found two relatively simple ways to solve it. First, I want to say that without a public IP, its impossible to connect reliably (in my experience).

When I proposed the solution, I explained the problem to other developers/managers this way.

Your server, the machine with the public IP address [public to clients, but may still be an "internal address"], is like a house without any long distance calling. It can receive calls, but it can't make any calls. The clients are like houses with long distance service. Clients must call the server, because they have long distance. Once connected, any party can talk on the line.

From here you have two choices.

  1. Client connects and never disconnects (this is what I implemented). On the server, I had an object that mapped the client object to the client connection so I could communicate any time with a client that was connected.

  2. Server holds a queue of messages for the client. The client automatically connects on a fixed interval to see if there are any messages (maybe 5 minutes). There would be an option from the server to stay connected for a specific interval. Another vendor called this "fast talk".

Upvotes: 3

Jonas Jämtberg
Jonas Jämtberg

Reputation: 571

The Windows Azure servicebus may have a solution for your problem; NetTcpRelayBinding in hybrid mode allows two comuters behind NAT to create a direct connection with each other. This might not solve your problem if you are money constrained as each connection has an associated cost.

The simplest solution is probably to have the clients polling your server.

Upvotes: 0

Daniel James Bryars
Daniel James Bryars

Reputation: 4621

There's a couple of approaches.

You could setup NAT - probably no good for your scenario. You could make an outbound connection from your client.

You could "combine the above" by using STUN (see http://en.wikipedia.org/wiki/STUN) this is quite popular in VOIP for peer to peer scenarios.

Upvotes: 1

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