Jarolin, Robert a �crit :
I discovered what the problem was with the dissection.
It turns out that "tcp_dissect_pdus" does not work properly if the
packet(s) have "TCP CHECKSUM INCORRECT"
I took the data (4 packets) that had the data segmented and rebuilt
the packet header data including the TCP header using text2pcap.
When I tried to dissect these packets (that now had proper TCP
checksums), my dissector correctly desegmented the data.
I then edited the packets to just change the TCP checksum and tried
again. The packets can no longer be desegmented.
This is the normal wireshark behavior.
Any ideas what to do about this issue?
Turn off "Validate the TCP checksum ..." into Edit / Preferences /
Protocols / TCP.
Olivier
Thanks.
See my original message below:
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
I have a dissector that uses tcp_dissect_pdus that does not seem to be
doing the job. Please help.
I have a dump that contains 4 TCP packets that are all related to the
same message (a total of 4428 bytes).
The first 3 packets are a length of 1460 bytes and the last 48 bytes
=> 1460 * 3 + 48 = 4428
When dissection takes place, the desegmentation does not seem to
properly occur.
Under the TCP portion of the dissection it properly says:
[PDU Size: 4428]
But the data available for dissection is only the size of the first
packet (1460)
What I am doing wrong? Thanks for any help.
Below are excerpts from my dissector:
#define FRAME_HEADER_LEN 4
*static void*
*dissect_myproto_message(tvbuff_t *tvb, packet_info *pinfo, proto_tree
*tree)*
{
/* Check that there's enough data */
total_len = tvb_length(tvb);
printf("Total_len = %u\n", total_len); //* THIS prints 1460*
.
// Dissect my data
.
}
*static guint*
*get_myproto_message_len(packet_info *pinfo, tvbuff_t *tvb, int offset)*
{
guint length = 0;
// myproto message (length is 2 bytes starting at offset 0 * 4)
length = (guint) ( tvb_get_ntohs( tvb, offset ) * 4 ); // Get the
length
printf("TOTAL of mesage = %u\n", length); //* This prints 4428*
return length;
}
/* Code to actually dissect the packets */
*static void*
*dissect_myproto(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)*
{
tcp_dissect_pdus(tvb, pinfo, tree, TRUE, FRAME_HEADER_LEN,
get_myproto_message_len, dissect_myproto_message);
}
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