--- On Mon, 3/7/11, Jeff Morriss <[email protected]> wrote:
From: Jeff Morriss <[email protected]> Subject: Re: [Wireshark-dev] TCP dissector handling TCP Fast Retransmit To: "Developer support list for Wireshark" <[email protected]> Date: Monday, March 7, 2011, 10:09 AM Gerald wrote: > Hi all, > > I'm working on a dissector for a TCP-based protocol, and I'm wondering if > there is any good way to handle when a TCP retransmit/fast retransmit occurs > in the middle of the stream. > > I will try to explain what is happening in one test case. > > First my dissector is called with some data. The TCP response spans many TCP > packets, so I keep setting pinfo->desegment_offset to 0 and > pinfo->desegment_len = DESEGMENT_ONE_MORE_SEGMENT. > > After about 5 packets there is a TCP retransmission of the first packet, and > the retransmitted data is sent to the dissector. > > Then the data that should have been next in the stream is sent to the > dissector, but without any of the previous data, leaving the dissector unable > to handle it. > > So I guess I have 2 questions. > > 1) Is there any way to handle this elegantly so that I can get a good > dissection that ignores the retransmitted data? > > 2) Barring #1, is there any (hopefully simple) way to determine if the data > received by the dissector is retransmitted data? I've spent a little time in the past few days looking at this issue, based on this thread: http://www.wireshark.org/lists/wireshark-dev/201103/msg00016.html I got a couple of (private) captures off-list that show where the TCP desegmentation stuff is breaking in the face of retransmissions and have been trying to figure out what is going on and how to fix it. Stay tuned. ___________________________________________________________________________ Thanks. If it makes any difference, I have discovered that if I go through and manually ignore the retransmissions in the UI, the reassembly works fine.
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