Wireshark mailing list archives

Re: Problems with dissecting fragmented packets


From: Jeff Morriss <jeff.morriss.ws () gmail com>
Date: Thu, 18 Nov 2010 12:41:19 -0500

Yosi Saggi wrote:
Hi ,

I'm writing a dissector for our LTE PHY packets. I have started working 
on fragmented packets. These are Ethernet packets that are fragmented 
with some proprietary limitation. Nevertheless we have a PI header 
(under the Ethernet header) that is always there in any fragment. The PI 
header contains what I thought is sufficient data for the fragment 
functions such as: size - the size of the PI message payload, Fragment 
(full, first, mid and last for indication as in what part of the 
fragmented packet are we) and sequence - message sequence index. I have 
used the "fragment_add_seq_check()" and the "process_reassembled_data()" 
functions to reassemble the packets but with no success. I get no 
reassembled packets. Only an indication on the fragments. I followed the 
"How to reassemble split packet" section 9.4 in the developers guide. I 
also went through the code over and over and see no problem. It seems 
that there is no use for the "LAST" indication of the fragmentation. 
After the last one I should have got a reassembled packet.

I'm no reassembly expert, but are you sure the code you quoted is called 
even when (!tree)?  The reassembly code only works on the first pass 
(when tree is NULL).
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