[Winpcap-users] losing transmitted packets

[Imre Magyar]

Hello all,

I have a win32 app that calls pcap_send() in a tight loop repeatedly, on the same 1400 byte frame, say 1000 times.

The PC is wired directly to an embedded 10/100 network device, but I do have a port aggregating tap device in between for monitoring. There are no switches or hubs involved at all.

I'll run the win32 app, and see that only a small fraction (say 500) of the frames are reported as received on the device at the other end.

If I run wireshark on the tap device, I see that the receiving device reported the frame count accurately. Only 500 went out on the link.

If I run wireshark on the PC on the same interface the app is sending the frames on, I see all 1000 frames.

If I insert a small delay in the app between pcap_send() calls (say I call Sleep(1) for a millisecond's worth of delay), all 1000 frames go out on the link, albeit much slower than I'd like.

Can anyone tell me what is dropping the frames and why? I'm assuming I'm overrunning some internal transmit buffer somewhere, but I'm at a loss to understand how to recognize it and when to back off. The pcap_send() function never returns with an error.

Thanks for any advice,

--Imre M.

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