Binding 40 Sockets to 40 different IP addresses

Question

I am writing on UDP server/client application.

I want my single server to handle 40 clients at a time. For this, I want to create 40 dedicated threads, each dedicated for one single client. Since there are 40 threads one for each client, I want to create 40 dedicated sockets as well.

But the problem that:

I don't know what will be the 40 IP addresses to which I shall bind() my sockets. (since as far as I now, I have to bind() to my Server\s IP address.) Normally I bind() to "INADDR_ANY" when there is only single socket.

But what should be the IP addresses at which I should bind() each of my 40 sockets? Please help me. Any comment/ help is appreciated.

Answer 1

bind only needs the local address, not the remote address.

If you want one socket for each client, then you'll need to use different ports for each (using bind). That way, each client can send its traffic to a dedicated port, and you can have a thread for each socket/port.

It's probably a better idea to only have one socket (and one port) though, and have logic in your code to assign traffic to a thread based on the remote address (retrieved using recvfrom eg.).

Answer 2

One common way to do this with UDP is:

• Server bind() to a well known port.
• Client sends the initial packet to that well known port
• Server receive the first packet from a client on the well known port.
• Server creates a new socket with a random port
• Server replies to the client from this new socket.
• Client receives the reply, notices it comes from another port than the well known server port, and uses that port as the destination for further communication.

You'll use the getpeername() call to learn the remote address.

Keep in mind that UDP is connection-less, you'll need some way to signal the end or time out you sockets.