Why does the port scanner only connect to one port?

Question

Computer networks

Wrote a simple port scanner on asynchronous sockets. Connection when scanning mail.ru and range [1; 1024] can only be installed on port 25, on the rest - unsuccessfully. The main() part :

port_range range; //structure for saving range of ports

(std::cin >> range.from >> range.to).get();

con_list cons; //std::vector of structures with sockets
sockaddr_in server_data;
u_long cmd = 1;
fd_set write;
timeval wait_time = { 0, 0 };
USHORT port = range.from;

server_data.sin_family = AF_INET;
tmp.s_addr = *(u_long*)remote_host_info->h_addr;
inet_pton(AF_INET, (PCSTR)inet_ntoa(tmp), &server_data.sin_addr);

while (true)
{
    //CONNECTION PHASE
    if (port <= range.to)
    {
        SOCKET sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
        server_data.sin_port = htons(port);

        if (sock == INVALID_SOCKET)
        {
            output_error("Couldn't create scan socket");
            finalize(); //WSACleanup(), system("pause")

            return EXIT_FAILURE;
        }
        //else
            //std::cout << "Created" << std::endl;

        if (ioctlsocket(sock, FIONBIO, &cmd) == SOCKET_ERROR)
        {
            error_to_close_cons("Couldn't put the socket in asynchronous mode", cons); //closes all created sockets, clears con_list container
            error_to_close_socket("", sock);
            finalize();

            return EXIT_FAILURE;
        }
        //else
            //std::cout << "Async" << std::endl;

        cons.push_back({ sock, 0, con_mode::write, port, 0, clock() });

        if (connect(sock, (SOCKADDR*)&server_data, sizeof(server_data)) == SOCKET_ERROR)
            if (WSAGetLastError() != WSAEWOULDBLOCK)
            {
                error_to_close_cons("Couldn't connect", cons);
                error_to_close_socket("", sock);
                finalize();

                return EXIT_FAILURE;
            }
        //else
            //std::cout << "Connected" << std::endl;
    }

    port++;

    //SCAN PHASE
    delete_invalid_cons(cons); //deletes structures with INVALID_SOCKET
    FD_ZERO(&write);

    if (cons.empty())
        break;

    for (u_int i = 0; i < cons.size(); i++)
        FD_SET(cons[i].sock, &write);

    if (select(0, NULL, &write, NULL, &wait_time) == SOCKET_ERROR)
    {
        error_to_close_cons("Couldn't perform client loop", cons);
        finalize();

        return EXIT_FAILURE;
    }
    //else
        //std::cout << "Selected" << std::endl;

    for (u_int i = 0; i < cons.size(); i++)
        if (FD_ISSET(cons[i].sock, &write))
        {
            std::cout << "Connection established on port " << cons[i].con_port << " in " << (clock() - cons[i].con_time) / CLOCKS_PER_SEC << " seconds" << std::endl;

            close_socket(cons[i].sock);
            cons[i].sock = INVALID_SOCKET;
        }
        else
        {
            std::cout << "Waiting time exceeded" << std::endl;
            close_socket(cons[i].sock);
            cons[i].sock = INVALID_SOCKET;
        }
        //else
            //std::cout << "Couldn't scan" << std::endl;
}

finalize();

return EXIT_SUCCESS;
}

Header snippet:

#pragma once
#ifndef WINSOCK_ERROR
#define WINSOCK_ERROR

#include <WinSock2.h>
#include <Windows.h>
#include <iostream>
#include <cstdlib>
#include <vector>
#include <cstring>
#include <ctime>

#define ECHO_PORT 32768
#define WSA_VERSION 0x0202
#define LOCALHOST "127.0.0.1"
#define BUFF_SIZE 8192
#define BACKLOG 4
#define WAIT_TIME 10
#define INPUT_BUFF 16


namespace con_mode
{
    enum mode
    {
        write,
        read,
        input //for client
    };
}

typedef struct async_connection
{
    SOCKET sock;
    int buffer_pos; //position in buffer
    con_mode::mode c_mode; //defines in which mode (recv/send) a socket works (for single-channel applications)
    //char* buffer; //for message from client
    USHORT con_port;
    int address_num; //address number in HOSTENT struct
    clock_t con_time;
} async_connection;

typedef struct port_range
{
    USHORT from;
    USHORT to;
    bool error_flag;
    char* error_message;
} port_range;

typedef std::vector<async_connection> con_list;

Another scanner, under the same conditions, established a connection on a larger number of ports.

Answer 1

nmap -O mail.ru
Starting Nmap 6.40 ( nmap.org ) at 2017-08-14 14:08 MSK
Nmap scan report for mail.ru (94.100.180.200)
Host is up (0.13s latency).
Other addresses for mail.ru (not scanned): 217.69.139.201 217.69.139.200 94.100.180.201
Not shown: 986 filtered ports
PORT STATE SERVICE
25/tcp closed smtp
53/tcp open domain
80/tcp open http
etc...
and ping mail.ru gives
PING mail.ru (94.100.180.201) 56(84) bytes of data.
64 bytes from mail.ru (94.100.180.201): icmp_seq=1 ttl=49 time=483 ms
see the difference in ip?
Other than that
$ nslookup mail.ru
Server: 127.0.1.1
Address: 127.0.1.1#53
Non-authoritative answer:
Name: mail.ru
Address: 217.69.139.200
Name: mail.ru
Address: 94.100.180.201
Name: mail.ru
Address: 94.100.180.200
Name: mail.ru
Address: 217.69 .139.201
In addition, the line Other addresses for mail.ru (not scanned): 217.69.139.201 217.69.139.200 94.100.180.201
there are other addresses ....
so what mail.ru are you talking about ??? By the way, other IPs give a different result, I checked (but not all ...).

Answer 2

If you are running a scan under Windows, then connections to ports 25, 80, etc. are usually intercepted by antivirus or services like alg (application layer gateway). On mail.ru port 25 is closed. The fact that you were able to connect to it simply means that some application has intercepted the connection.
Everything is wrong here. From what immediately catches the eye:
1. server_data must be set to zero before use
2. FD_SET supports only 64 sockets by default (on Windows, *nix also has a limited number). Accordingly, you scan only the first 64 ports
3. connect() will not give you a connection error, because you switched the socket to asynchronous mode, so in most cases you will have waiting time exceeded, although in fact the error will be different.
4. there is a feeling that a piece of code is cut out, because the socket check got into the same cycle where the connections go.