Creating a heavily restricted server discovery application in c#

Question

Dear community.

I am writing you because of a new problem I need to solve, and I have now been banging my head against a wall for too long now.

Basically, I need to create an application that can take care of the following:

A user starts an app, which sends a broadcast to the subnet, and recieves a response of all servers there with their IP (and some additional info). The user can then select what server he wants to connect to.

Making it work is simple enough, with identifying the subnet, and broadcasting with UDP, and then having a different server application recieving it and sending back a response . The problem lies with these restrictions, that I need to take into consideration:

• There will most likely also be clients on the server machines in the network, meaning that we can assume that the application is present on all machines. Every machine needs to have the listener running, and every machine can launch the GUI for selecting a server.
• I am only allowed to add one exception to the firewall - an exception that handles both sending out the broadcasts, recieving broadcasts, sending answers and recieving answers.
• I should also only be adding one Windows Service
• on a server machine, the listener should run as a windows service, so the user won't notice it. Nor will the user notice, that the response is sent back to the client.
• On the client machine, the user can start an application, which will notify the application to emmit the broadcast, and will get all the server responses, so the user can choose one to connect to.
• Besides from the application that the user launches in order to select a server, there should be no interaction with the user whatsoever. Not even a popup, requesting the user to allow traffic trough the firewall - it should all be automatically
• It needs to work on and in between Win XP, Win Vista and Win 7.

I don't know if I am putting too many constrains on myself, but I really hope that I can make the application with these requirements.

I have a few ideas - I just need to figure out how to do it:

• Should i make everything into one application, that I add to the firewall exception list, so it will take care of the traffic on both the server and the client machines?
• Should I add a custom exception to the firewall, allowing UDP traffic on a specific port, and then have all traffic flow trough that?
• Is there a third and better option for managing that?
• It is OK to have the service running on both client and server machines. But can it take care of everything for me - like it handling both the broadcast send/recieve and answer send/recieve? And is there any way to extract the information about servers on the network from a service?

I know it is a lot, but I really hope that you will be able to help me out.

let me know if I wasn't clear enough, or if you need further explanations.

I am coding in C# .Net, and I can utilize all I want from the .Net framework. As soon as I have this functionality implemented

All the best

/Sagi

Answer 1

The kind of peer-to-peer networking problems become simple to the point of being trivial if you designate one machine as the master server. It should have a well-known name that all sub-servers can connect to so they can publish (and withdraw) their availability. A client can then send a query request to the same server and get a list of known servers in return.

This can also solve your firewall problem, the master server could be listening on port 80.

Look into the System.Net.PeerToPeer namespace for a p2p solution supported by the framework.

Answer 2

Maybe a UPnP server and client may be a solution to your problem?