Соккеты.

...
sockaddr_storage connection_address;
        while ( 1 )
        {
            int connection_socket = get_new_connection_socket(local_socket, connection_address);
            if ( connection_socket == -1 )
            {
                std::cout << "accept: not valid descriptor!n";
                continue;
            }
            show_connection_address(connection_address);
            send_message(local_socket, connection_socket);
            close(connection_socket);
        }
...
void send_message(int& local_socket, int& connection_socket)
{
    if ( !fork() )
    {
        close(local_socket);
        char message [50] = "Connect to me again, client!\n";
        int result = send(connection_socket, message, sizeof(message), 0);
        if ( result == -1 )
        {
            std::cout << "send: error!\n";
        }
        close(connection_socket);
        exit(0);
    }
    else
    {
        std::cout << "fork: no child process was created!\n";
    }
}
...