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Old 09-03-2009, 11:40 AM   #1
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Registered: Aug 2009
Posts: 21

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UDP packets not seen with wireshark when sending too fast

Hello network experts,

I have problems debugging my 100MBit/s ethernet communication between a dedicated Intel network card an a microcontroller (MC) board. The MC is directly connected to the pc with a 1 meter ethernet cable. Network card and MC have fixed IPs and the UDP communication works in most cases.
Now I want to send 100000 bytes to the MC and do so by sending UDP packets of about 1000 bytes each.
The pc has wireshark running to see all the packets.
My program always successfully sends all the packets with "sendto" (see the function below). But wireshark only sees all the packets when I introduce a "usleep(100)" between the "sendto" commands. Sending the packets without waiting results in that wireshark just sees the first few packets.

Where are the missing packets?
I know that UDP does not guarantee the packets to arrive, but AFAIK they should at least be sent.

Please help,

int send_data( char *buffer, int buf_length )
  int rc = sendto (sock, buffer, buf_length, 0,
               (struct sockaddr *) &pmi_addr,
  if (rc < 0) 
    printf ("could not send data\n");
    close (sock);
    exit (EXIT_FAILURE);
  if (rc != buf_length) 
    printf ("could not send whole data block\n");
    close (sock);
    exit (EXIT_FAILURE);

Last edited by mibo; 09-04-2009 at 05:41 AM. Reason: solved the problem
Old 09-04-2009, 03:31 AM   #2
LQ Newbie
Registered: Aug 2009
Posts: 21

Original Poster
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I rechecked with wireshark.
The used eth1 device is in promiscous mode and the status bar of wireshark shows NO dropped packets - so everything seems to be fine, except that the later packets still don't appear :-(

Any hint?

Edit: I found the reason for the missed packets. There was a computation running in the background. Now, when the quad core pc is idle - wireshark shows all the packets.

BUT - why the hell didn't wireshark report that it was missing packets?

Last edited by mibo; 09-04-2009 at 05:40 AM.


loss, packet, udp, wireshark

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