Find the next TCP port in .Net

Question

I want to create a new net.tcp://localhost:x/Service endpoint for a WCF service call, with a dynamically assigned new open tcp port.

I know that TcpClient will assign a new client side port when I open a connection to a given server.

Is there a simple way to find the next open TCP port in .Net?

I need the actual number, so that I can build the string above, 0 does not work, since I need to pass that string to another process, so that I can call back on that new channel.

Answer 1

Use a port number of 0. The TCP stack will allocate the next free one.

Answer 2

First open the port, then give the correct port number to the other process.

Otherwise it is still possible that some other process opens the port first and you still have a different one.

Answer 3

Here is what I was looking for:

static int FreeTcpPort()
{
  TcpListener l = new TcpListener(IPAddress.Parse("127.0.0.1"), 0);
  l.Start();
  int port = ((IPEndPoint)l.LocalEndpoint).Port;
  l.Stop();
  return port;
}