Wireshark-bugs: [Wireshark-bugs] [Bug 5971] New: Support for TCP dissector to handle Out-Of-Orde

Date: Sun, 29 May 2011 17:14:23 -0700 (PDT)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=5971

           Summary: Support for TCP dissector to handle Out-Of-Order
                    packets when the first fragment of up-level PDU is
                    retransmitted
           Product: Wireshark
           Version: 1.7.x (Experimental)
          Platform: Other
        OS/Version: Windows 7
            Status: NEW
          Severity: Major
          Priority: Low
         Component: Wireshark
        AssignedTo: wireshark-bugs@xxxxxxxxxxxxx
        ReportedBy: dmitrmax@xxxxxxxxx


Max Dmitrichenko <dmitrmax@xxxxxxxxx> changed:

           What    |Removed                     |Added
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   Attachment #6424|                            |review_for_checkin?
               Flag|                            |

Created an attachment (id=6424)
 --> (https://bugs.wireshark.org/bugzilla/attachment.cgi?id=6424)
Patch

Build Information:
Paste the COMPLETE build information from "Help->About Wireshark", "wireshark
-v", or "tshark -v".
--
There were several discussions regarding TCP dissector behavior when the first
fragment of application level PDU is lost and retransmitted later. I wrote a
patch which handles this problem with the assist from up-level subdissector.

Brief description of how to use this feature. Up-level subdissector has to
track tcp_info->seq for both flow directions to detect out-of-order tvb's. When
this situation is detected subdissector has to request packet desegmentation
setting pinfo->desegment_len to DESEGMENT_OUT_OF_ORDER and
pinfo->desegment_offset to the offset of the expected in-order packet relative
to the received out-of-order packet. The later generally is the negative value
which equals to (tcp_info->seq - expected_seq). And that's all! Certainly the
subdissector must be prepared to handle TVBs which contain multiple application
layer PDUs.

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