[Winpcap-bugs] Re: Checksum errors on Windows XP Professional x64Edition

[Gianluca Varenni]

Actually both the messages were archived here http://www.winpcap.org/pipermail/winpcap-bugs/2006-October/date.html

Regarding your issue, it's not actually a bug in WinPcap. Your network card performs TCP and IP checksum offloading i.e. the TCP and/or IP checksums of outbound packets are not computed by the TCP/IP stack, but rather by the network card itself. In fact the packets with a wrong checksum are only the outbound ones (from  192.168.1.101), and the "wrong" value is 0000. WinPcap captures on top the network card, before such checksum is computed. 

Most of the network cards have an option (in their configuration panel) to disable the checksum offloading. If you disable it, you'll see correct checksums.

Hope it helps
GV


  ----- Original Message ----- 
  From: No Name 
  To: winpcap-bugs at winpcap.org 
  Sent: Monday, October 23, 2006 5:34 AM
  Subject: [Winpcap-bugs] Re: Checksum errors on Windows XP Professional x64Edition


  Hi,

  Below is the original text for this message. For some reason I can't see it on the archive page.

  Thanks,
  No Name

  --

  Hi,

  I am running WinPCAP 4.0 Beta 2 on WXP x64 Edition. Even the simplest test shows numerous checksum errors while capturing TCP (perhaps also UDP - I haven't tried it out). I understand that x64 support must be preliminary, but this data is very basic when using captures. 

  Attached are "windump -D", adapters.reg & npf.reg as well as 2 captures I performed of the same traffic. Both captures were made with Ethereal 0.99.0. Checksum errors also occur with Wireshark 0.99.3:

  Cap1 - captured from the x64 computer.
  Cap2 - captured from a VMware virtual machine running Windows XP Professional (x86) with the same version of WinPCAP.

  Please advise.

  Best regards,
  No Name





------------------------------------------------------------------------------


  _______________________________________________
  Winpcap-bugs mailing list
  Winpcap-bugs at winpcap.org
  https://www.winpcap.org/mailman/listinfo/winpcap-bugs
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.winpcap.org/pipermail/winpcap-bugs/attachments/20061023/e12c50dd/attachment.htm