[Winpcap-users] Problem gathering bytes statistics on Ethernet devices

Boaz Brickner boaz.brickner at gmail.com
Thu Jul 2 21:55:16 PDT 2009


I'm using Windows XP Professional SP3 with Atheros AR8121/AR8113 PCI-E
Ethernet Controller.

I'm following the statistics part of the tutorial:

I'm sniffing the packets I'm sending and I'm sending a batch of Ethernet
packets to my Ethernet device.
If I send N packets with size 60 or greater, I'm receiving all the N packets
using the statistics mode.
However, when I look at the "AcceptedBytes" field according to the winpcap
tutorial, I'm receiving exactly 12 bytes more per packet sent.

Example: If I send 10 packets of 60 bytes, I receive in the statistics mode
10 packets and 720 bytes (instead of 600).
Example: If I send 100 packets of 500 bytes, I receive in the statistics
mode 100 packets and 51,200 bytes (instead of 50,000).

My guess is that it has something to do with the Ethernet Preamble /
Start-of-Frame-Delimiter / Interframe gap fields of the Ethernet protocol
since these fields are not part of the sniffed (or sent) packet.
I'm not sure exactly why these 12 bytes are added to the statistics and
would like to know for statistics analysis.

By the way, if I send packets with less than 60 bytes. The difference I
receive per packet is 12 bytes + the number of bytes complementing to 60
bytes. This is obvious since the minimum Ethernet packet size is 60 bytes.

Example: If I send 100 packets of 25 bytes, I receive in the statistics mode
100 packets and 7,200 bytes (and not 2,500).

Thank you,

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