I have a dissector which can read 2 udp packets and combine data from those.
Every time I select a packet (N) that is based on combining data from previous packet (N-1
) and current packet (N), I'm getting an error on the packet details on the custom protocol section.
Only when I select previous packet (N-1) and then the current packet (N), I can see the dissection as I expect and without any error.
Any idea how to solve the issue?
Related
Is it possible to re-do numbering in Wireshark. For example i have filtered packets to one side:
So the numbers are (they are not in order because of filtering):
416,419,420,423,424,426,427.
But i would like to number them like this, line by line:
1,2,3,4,5,6,7
The reason is that it would be easier to count all the packets. I know tshark has statistical operation COUNT, but for quick counting this would be a lot better.
You can export the displayed packets into a new file via File -> Export Specified Packets... -> All packets: Displayed. The new capture file will contain sequentially numbered packets starting from 1.
But if you just want to know how many displayed packets there are, you could just look at the Wireshark status line where it will indicate the number of displayed packets.
Statistics -> Capture File Properties will also tell you the number of displayed packets.
I have wrote a plugin to analyze (translate to different Protocol name) packet in Wireshark with LUA APIs. All I needed to do to only analyze packets that shows UDP or TCP in Wireshark. I am using that following code to get protocol value:
pinfo.cols.protocol
to only analyze the packets that will show as TCP or UDP in Protocol column.
Sometime it retrains the value that is in Protocol column (e.g. TCP, SSH, or ...) but most of the time it returns "(protocol)".
How can I fix it? Is there any way possible that I can figure it out?
Thanks
I have a very large tcpdump file that I split into 1 minute intervals. I am able to use tshark to extract TCP statistics for each of the 1 minute files using a loop code and save the results as a CSV file so I can perform further analysis in Excel. Now I want to be able to count the number of TCP flows in each 1 minute file for all the 1 minute files and save the data in a CSV file. A TCP flow here represents group of packets going from a specific source to a specific destination. Each flow has statistics such as source IP, dest IP, #pcakets from A->B, #bytes from A->B, #packets from B->A, #bytes from B->A, total packets, total bytes, etc. And I just want to count the number of TCP flows in each of the 1 minute files. From what I’ve read so far, it seems I need to create a dissector to do that. Can anyone give me pointers or code on how to get started? Thanks.
Tshark has a command to dump all of the necessary information: tshark -qz conv,tcp -r FILE. This writes one line per flow (plus a header and footer) so to count the flows just count the lines and subtract the header/footer.
Not a dissector, but a tap. See the Wireshark README.tapping document, and see the TShark iousers tap for a, sadly, not at all simple example in C.
It's also possible to write taps in Lua; see, for example, the Lua/Taps page in the Wireshark Wiki and the Lua Support in Wireshark section of the Wireshark User's Manual.
The C structure passed to TCP taps for each packet is:
/* the tcp header structure, passed to tap listeners */
typedef struct tcpheader {
guint32 th_seq;
guint32 th_ack;
gboolean th_have_seglen; /* TRUE if th_seglen is valid */
guint32 th_seglen;
guint32 th_win; /* make it 32 bits so we can handle some scaling */
guint16 th_sport;
guint16 th_dport;
guint8 th_hlen;
guint16 th_flags;
guint32 th_stream; /* this stream index field is included to help differentiate when address/port pairs are reused */
address ip_src;
address ip_dst;
/* This is the absolute maximum we could find in TCP options (RFC2018, section 3) */
#define MAX_TCP_SACK_RANGES 4
guint8 num_sack_ranges;
guint32 sack_left_edge[MAX_TCP_SACK_RANGES];
guint32 sack_right_edge[MAX_TCP_SACK_RANGES];
} tcp_info_t;
So, for C-language taps, the "data" argument to the tap listener's "packet" routine points to a structure of that sort.
For Lua taps, the "tapinfo" table passed as the third argument to the tap listener's "packet" routine is described as "a table of info based on the Listener's type, or nil.". For a TCP tap, the entries in the table include all the fields in that structure except for sack_left_edge and sack_right_edge; the keys in the table are the structure member names.
The th_stream field identifies the connection; each time the TCP dissector finds a new connection, it assigns a new value. As the comment indicates, "this stream index field is included to help differentiate when address/port pairs are reused", so that if a given connection is closed, and a later connection uses the same endpoints, the two connections have different th_stream values even though they have the same endpoints.
So you'd have a table using the th_stream value as a key. The table would store the endpoints (addresses and ports) and counts of packets and bytes in each direction. For each packet passed to the listener's "packet" routine, you'd look up the th_stream value in the table and, if you don't find it, you'd create a new entry, starting the counts off at zero, and use that new entry; otherwise, you'd use the entry you found. You'd then figure out whether the packet was going from A to B or B to A, and increase the appropriate packet count and byte count.
You'd also keep track of the time stamp. For the first packet, you'd store the time stamp for that packet. For each packet, you'd look at the time stamp and, if it's one minute or more later than the stored time stamp, you'd:
dump out the statistics from the table of connections;
empty out the table of connections;
store the new packet's time stamp, replacing the previous stored time stamp.
I have a number of packet captures in pcap format. Each packet contains a message for which I have dissector however each packet has 4 bytes prepended to it. This means the dissector will not understand the format.
Is there anyway for me to mangle these captures such that they come out the other end with those 4 bytes stripped off?
You will need to edit at least one dissector to do what you want. The best thing to do is to write a dissector that will handle the header inserted by your B protocol, against which the C protocol dissector would need to register. This gives you the added benefit of being able to examine information in the header of the B protocol and filter on its fields.
However, if you really don't want to do that, you could modify either the A protocol or C protocol dissector to ignore those four bytes: in A, you would not include those bytes in the tvb given to C; or in C you would skip the first four bytes in the tvb.
editcap.exe -L -C <num> <infile> <outfile>
Google: "man edicap"
When writing a dissector in Wireshark, is the dissect function in the dissector's source called on each packet in order, only once?
What could be possible reasons for tree values changing as I click on packets multiple times?
It is called once when the packet is first to display the high level information.
if (check_col(pinfo->cinfo, COL_PROTOCOL))
or
if (check_col(pinfo->cinfo,COL_INFO))
And called again when showing the body, ie when you click on that one packet.
if (tree)
I'd assume that the second call results are discarded, as if you have a large number of packets to decode keeping the details for each would be too large an overhead.
But as always some quick testing would be able to show if this is the case. (via a static counter)