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Re: [Wireshark-commits] master 104a6ed: Disable IPv4 checksum verfification to match TCP and UDP.
From: Jasper Bongertz <jasper.sharklists () packet-foo com>
Date: Sun, 2 Mar 2014 15:14:14 +0100

On Sat, Mar 01, 2014 at 01:49:58PM +0000, Wireshark code review wrote:
URL: https://code.wireshark.org/review/gitweb?p=wireshark.git;a=commit;h=104a6edd1fb703c5c2319c893720df86f8c9a9e7
...
104a6ed by Gerald Combs (gerald () wireshark org):

    Disable IPv4 checksum verfification to match TCP and UDP.
    
    Offloading seems to be very common nowadays and having this option
    enabled by default generates a lot of false positives. Suggested by
    Laura Chappell.
    
    Change-Id: I285f218efb3c9f164d8ad7a6d6de8270e442ffff

While this is currently the right thing to do, it might make more sense
to disable all this checksum verification stuff only for outgoing traffic.
Unfortunately our current captures don't support that distinction. What
would be required where to make this possible?
My guess:
- Add a metadata element "direction" to the capture information provided
  by the network driver and
- add "direction" element to libpcap packet header and fill it with the
  information from above.
How much work would that amount to?

The pcap-ng file format has "packet blog flags" in the EPB block type,
which has two bits to indicate direction (00 = information not
available, 01 = inbound, 10 = outbound). I don't think those flags are
being  set by dumpcap as of now, but it would be the way to go from my
point of view.

See
http://www.winpcap.org/ntar/draft/PCAP-DumpFileFormat.html#sectionepb
and http://www.winpcap.org/ntar/draft/PCAP-DumpFileFormat.html#appendixPBFM

Cheers,
Jasper



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