struct protoent       *pe;
  struct sockaddr_in    sin;
  int                   sock;
  struct sockaddr_in    sin_clt;
  int                   size_sin;

  if ((pe = getprotobyname("TCP")) == NULL)
      perro("getprotobyname");
  sock = xsocket(AF_INET, SOCK_STREAM, pe->p_proto);
  sin.sin_family = AF_INET;
  sin.sin_addr.s_addr = INADDR_ANY;
  while (bind(sock, (const struct sockaddr*)&sin,
              (socklen_t)sizeof(sin)) == -1 && server->port2 <= 65535)
    sin.sin_port = htons(server->port2++);

  if (listen(sock, 1) == -1)
    perror("listen");
  size_sin = sizeof(sin_clt);
  if ((server->pasv_sock = accept(sock, (struct sockaddr*)&sin_clt,
                                  (socklen_t*)&size_sin) == -1))