I am trying so sniff a multi-part POST request using Wireshark. When viewing the capture I can select "Reassembled TCP" which looks to contain the header and all the data in the transmission. However I can't seem to select the entire thing to save it. If I go back to the frame view i can select the frame, which usually selects the entire transmission, but it will only end up saving the post data.
How can I save the entire Reassembled TCP?
Use the "Follow TCP stream" option:
http://linuxonly.nl/docs/38/117_Wireshark.html
Ok, really simple one. There is a heading after "Transmission Control Protocol (TCP)" and "Hypertext Transfer Protocol" called "[Reassembled TCP Segments]" Selecting that allows you to save the Reassembled TCP Segments. Note to self to widen my focus a little.
Works for HTTP, DICOM or SMB streams only but there is a "Export Objects" option now.
You can access it from File -> Export Objects -> HTTP.
Related
I am trying to understand the output of network data captured by tshark using the following command
sudo tshark -i any ‘tcp port 80’ -V -c 800 -R ‘http contains <filter__rgument>' > <desired_file_location>
Accordingly, I get some packets in output each starting with a line something like this:
Frame 5: 1843 bytes on wire (14744 bits), 1843 bytes captured (14744 bits) on interface 0
I have some basic questions regarding a packet:
Is a frame and a packet the same thing (used interchangeably)?
Does a packet logically represent 1 request (in my case HTTP request)? If not, can a request span across multiple packets, or can a packet contain multiple requests? A more basic question will be what does a packet represent?
I see a lot of information being captured in the request. Is there a way using tshark to just capture the http headers and http reqeust body? Basically, my motive of this whole exercise is to capture all these requests to replay them later.
Any pointers in order to answer these doubts will be really helpful.
You've asked several questions. Here are some answers.
Are frames and packets the same things?
No. Technically, when you are looking at network data and that data includes the Layer 2 frame header, you are looking at a frame. The IP packet inside of that frame is just data from Layer 2's point of view. When you look at the IP datagram (or strip off the frame header), you are now looking at a packet.
Ultimately, I tell people that you should know the difference and try to use the terms properly, but in practice it's not an extremely important distinction.
Does a packet represent a single request?
This really depends. With HTTP 1.0 and 1.1, you could look at it this way, though there's no reason that, if the client has a significant amount of POST data to send, the request can't span multiple packets. It is better to think of a single "connection" or "session" as a single request/response. (This is not necessarily strictly true with HTTP 1.1, but it is generally true)
With HTTP 2.0, this is by design not true. A single connection or session is used to handle multiple data streams (requests/responses).
How can I get at the request headers?
This is far too lengthy for me to answer here. The simplest thing to do, most likely, is to simply fire up WireShark, go into the filter bar and type "http." As soon as you hit the dot, you will see a list of all of the different sub-elements that you can look at. You can use these in tshark using the '-Y' option, and you can additionally specify columns that you would like to display (so you can add and remove columns, effectively).
An alternative way to see this information is to use the filter expression button to bring up the protocols selector. If you scroll down to HTTP, you can select it and then see all of the fields that are available.
When looking through these, realize that some of the fields are in the top-level rather than within request or response. For example, content-length appears as a field under http rather than http.request.content_length. This is because content-length is a field common to all requests and responses.
Completely new to Wireshark and wondering how to extract the data from the TCP packets which I receive on wireshark.
I am currently using a raspberry pi with grove sensors and getting the values of pressure and temperature. I am sending these values to a server in cloud and it is working. I am using wireshark to trace the packets.
Now I want to extract the data (i.e the pressure value and temperature value) from the packets and store them in a file for further implementation. Is there a way to do it? If yes, then can anyone please explain? It will be helpful.
Thanks.
Most convenient way is saving whole TCP stream into file. Right click on any TCP packet of desired stream, choose "Follow -> TCP stream" and you will see window for managing stream data. You can choose, which data to save (one-direction, or both), which format will be used for output and so on. Check pict below:
The other way is saving data from any packet individually. Since you aren't interested in whole packet, you can select only payload part. Check picture below, where I selected HTTP part of the packet (I marked field with red arrow for clearance). In your case, it will be some field with raw data. Once highlighted the right field, right click on it, choose "copy" and select desired format. Data will be placed into buffer, so you need to paste it into some application. If raw binary is chosen for format, you need application capable of pasting binary data. I use frhed for this task.
I am new to writing dissectors in Lua and I had two quick questions. I have a packet which has the TCP Options as MSS, TCP SACK, TimeStamps, NOP, Window Scale, Unknown. I am basically trying to dissect the unknown section in the TCP Options field. I am aware that I will have to use the chained dissector.
The first question is while using the chained dissector to parse the TCP Options, do I have to parse all the Options from the beginning. For Example will I need to parse MSS, TCP SACK, .... and then finally parse Unknown section or is there any direct way for me to jump to the Unknown section.
The second question I have is I have seen the code for many custom protocol dissectors and if I need to dissect a protocol which follows (for example)TCP, then I will have to include the following:
-- load the tcp.port table
tcp_table = DissectorTable.get("tcp.port")
-- register our protocol to handle tcp port
tcp_table:add(port,myproto_tcp_proto)
My question is, is there anyway for me to jump to the middle of the protocol. For example in my case I want to parse TCP Options. Can I directly call tcp.options and the parser will start dissecting from where the options will start?
The TCP option is "uint8_t type; uint8_t len; uint8_t* data" structure.
I usually give common used ones a name. For example getSack(), getMss().
For others, keep them in an array(maximum size like 20).
For your second question, you mean you don't care about TCP header, right? If so, just move your pointer 20 bytes further to get access the TCP options.
I want to use iperf to send some packets and receive the same at the client (which might have gone through different OSI layer processings). I want to check the packets sent are same as the received ones.
Can I use Wireshark to capture the streams?
Is there any way to compare them with the wireshark?
Or is there any other better way of doing this?
You can use Wireshark to perform the capture, select the packets of each stream and export to text files (one per stream):
File -> Export -> as "Plain Text" file:
- Check "Selected packet only"
- Check "Packet summary line"
- Check "Packet details: All expanded"
Then perform the diff with regular text tools as gnu diff, WinMerge or gvimdiff.
yes you'll be able to but this will be difficult as the goal of iPerf is to send a lot of packets, the capture will include a big flow of it.
strangely there is not a diff-like tool to compare 2 captures. Instead the doc[1] propose a workaround : to merge both and stats on their diffs.
NB :I wonder myself doing such a usefull tool,in addition this is in the Wireshark wishlit.
[1] source : http://www.wireshark.org/docs/wsug_html_chunked/ChStatCompareCaptureFiles.html
Here's an example 'Packet Structure' image: http://freesoft.org/CIE/Course/Section3/7.htm
Lets say I had a small Python program that listened on X port and captured that packet and saved it to the variable 'data'.
How would I pull out the packet information from data? For example, say I wanted to read the 'version', is it just:
print data[0:4] ?
How would I get the Source IP Address?
I've been doing more socket coding lately and have ran into quite a few of these 'packet structure' images. I'm yet to figure out how to apply them to my code :/
Note that your example shows an IP header - if you are simply using sockets, you will not see this information (its already been digested by the system IP and TCP stacks).
If you want to capture raw data, look into using libpcap, which will allow raw packets. You can also use tcpdump to produce a file with raw packets.
As for structures, you can read the first 4 bytes if your data was a string with your command. You would likely want to encode the string as "hex" (or integers for the normal representation) or you will see "garbage" characters instead.
For more powerful unpacking, use the struct module which comes with python.