Scanning Localhost

[Wasim <wasim.khan () gmail com>]

I have encountered a problem while writing code for scanning Localhost. The
problem is i did'nt get the destination port and source port of reply
correct. For e.g. if i set source port =62144 and destination port=22 then
i must get reply source port = 22 and reply destination port = 62144, but
that is  not the case. What can be the problem??? can any body help??? I
googled it but couldn't find any thing.
Here i'm putting the code where i'm sniffing:

struct pcap_pkthdr header;

  const u_char *packet;

  struct libnet_ipv4_hdr *ipHdr;

  struct libnet_tcp_hdr *tcpHdr;

  int reply_dstport = 0;
  int reply_sport =0 ;

  int timeout = 3;
  time_t start;
  start = time(NULL);

  /* capture packets until a timeout occurs or the required packet is
received */
  while ((time(NULL)-start) < timeout)
  {
    packet = pcap_next(pcapHandle, &header);

    if (packet == NULL)
    {
      continue;
    }
    else
    {
      ipHdr = (struct libnet_ipv4_hdr *)(packet + 14);
      tcpHdr = (struct libnet_tcp_hdr *)(packet + 14 + (ipHdr->ip_hl << 2));

      /* if ip packet is not from the expected host then skip this packet */
      if ((ipHdr->ip_src.s_addr != destination_ip))
        continue;

      cout << "IP of request and reply is Identical" << endl;
      int tprotocol; //transport protocol like tcp ,udp  tcp 0x06
      tprotocol = ipHdr->ip_p;

      if(tprotocol == 0x06)
      {
            /*here the problem occurs */
          reply_sport = ntohs(tcpHdr->th_sport);
          reply_dstport = ntohs(tcpHdr->th_dport);

        cout << "source port (reply) = " << reply_sport << endl;
        cout << "dest port (reply) = " << reply_dstport << endl;

      }
    }
  }

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