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Re: [Wireshark-commits] master 104a6ed: Disable IPv4 checksum verfification to match TCP and UDP.
From: Gerald Combs <gerald () wireshark org>
Date: Mon, 03 Mar 2014 09:52:19 -0800

On 3/2/14 6:14 AM, Jasper Bongertz wrote:
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.

It might make sense to fetch the offload settings for each interface and
adjust the checksum settings accordingly. We have offload code for
Windows but we currently only use it for the interface details dialog

In the meantime unless anyone objects I'm going to cherry-pick the
change to master-1.10 for inclusion in 1.10.6.
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