void Main()
{
    IPEndPoint localEP = new IPEndPoint(IPAddress.Any, 20000);
    
    Socket socket1;
    socket1 = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    socket1.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
    socket1.Bind(localEP);

    Socket socket2;
    socket2 = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    socket2.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
    socket2.Bind(localEP);
}