[Winpcap-users] Missing directed packets in VC++6

Gianluca Varenni gianluca.varenni at cacetech.com
Mon Aug 29 16:22:44 GMT 2005


I have no idea why your application does not "respond" to directed packets. Have  you tried using Windump or Ethereal and see if you actually receive those directed packets?

Regarding the MAC issue in V3.1, there is no guarantee that a MAC address is associated with a device (this is particularly true for the GenericDialupAdapter, that was added in WinPcap v3.1), that's the reason for the NULL pointer.

Hope it helps
  ----- Original Message ----- 
  From: Ewan MacPherson 
  To: winpcap-users at winpcap.org 
  Sent: Sunday, August 28, 2005 7:25 PM
  Subject: [Winpcap-users] Missing directed packets in VC++6

  I am using VC++ 6.0 to create an app. which uses Winpcap. If I use the app on the computer which contains the VC++ IDE etc. the app works fine. I have win2000.

  If, however, I install the app. on another (almost identical) computer on which I installed winpcap, the app. only responds to broadcast packets and not those directed to its MAC address. Yes, I changed the MAC address when installing in the new PC.

  All this is using Winpcap v3.0. When I uninstall v3.0 and install v3.1 a different strange thing occurs. In both the PC which "works" and the one which "doesn't work" I get a NULL pointer in "mac_ptr = get_mac_addr(adap);".

  When I go back to v3.0 I get the previous condition.

  Thank you for any help you can give.

  Here is the relevant code:-

  // pfx is defined in the class header file

  pcap_if_t     *d;
  char          mac[6];
  unsigned char *packet;                      // this is the pointer
  char          apacket[MAXBYTES];            // this is the actual packet
  int           NewCardPending;
  char          errbuf[PCAP_ERRBUF_SIZE+1];
  char          MACaddr[6];

  int pfx/**/MainProgram(void)             // from the start button to here
    pcap_if_t     *alldevs;
    char          *mac_ptr;                 // Pointer to returned MAC address
    char          mac2[6];
    ADAPTER       *adap;
    BOOL          bummer;
    FILE          *fp;
    char          check[128];

    /* Ethernet Initialization */
    fp = fopen("MACADDR.INI", "r");

    if (fp == NULL)
      m_Message.SetWindowText(CString("No MAC File"));
      return -1;

    fscanf(fp, "%s %x %x %x %x %x %x",
                &mac[0],                    // mac address of adapter
                &mac[1],                    // get from file

    if ((check[0] != '*') || (check[1] != 'M') || (check[4] != '*'))
      m_Message.SetWindowText(CString("Bad MAC File"));
      return -1;


    /* Retrieve the ethernet interfaces list */
    if (pcap_findalldevs(&alldevs, errbuf) == -1)
      m_Message.SetWindowText(CString("Cannot find Ethernet Adapters"));
      return -1;

    /* Scan the retrieved list */
    for(d = alldevs; d != 0; d = d->next)
      adap = PacketOpenAdapter(d->name);    // Initialize the pointer

      mac_ptr = get_mac_addr(adap);

      if (mac_ptr == NULL)
        m_Message.SetWindowText(CString("NULL Mac pointer"));
        return -1;

      memcpy(mac2, mac_ptr, 6);

      bummer = false;

      for (int i = 0; i < 6; i++)
        if (mac[i] != mac2[i])
          bummer = true;

      if (bummer == false)
        m_Message.SetWindowText(CString("Found Ethernet Adapter"));
        pfx/**/DoMainLoop();          // never return
    }                                 // try next device

    m_Message.SetWindowText(CString("No Matching Ethernet Adapter"));

    return 1;


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