I'm writing a dissector for a protocol that I have to work with. This protocol runs atop TCP and is stateful.
In order to dissect the fields correctly, I need to identify which endpoint opened the TCP connection (the client).
Is there a way to get this info from the tcp dissector? Would I have to write a tap? I'm not so clear on how to do this in lua.
Cross posted on the Wireshark stack site here.
To write stateful protocol dissector in Lua you can use closures to store state information.
you can easily decipher which endpoint started conversation if you analyse flags SYN/SYN+ACK for the first packets of given TCP stream # (which is generated by TCP dissector).
To make this work you should install a post dissector and check for 'tcp.stream' field.
You can checkout that technique in sources of my small Lua wireshark dissector to capture HTTP state information
Related
I am trying to debug an LWM2M protocol issue. I need to know what messages are transferred between the COAP server and the COAP client. As the traffic is encrypted using DTLS, I need to give the pre-shared key in wireshark to see the payload. Wireshark is successfully decrypting the payload, but I am not able to see the underlying COAP protocol messages. I am seeing just the raw data("Application data"):
But when I try sniffing unencrypted COAP traffic on a dummy setup, I could see the COAP messages properly:
How can I view the COAP protocol traffic using wireshark when it is encrypted?
The problem is that you're using a non-standard port number for COAPS instead of the IANA-registered port of 5684, and the Wireshark COAP dissector's proto_reg_handoff_coap() function only registers to the DTLS dissector with that fixed, non-configurable port (DEFAULT_COAPS_PORT). There are some possible ways to fix this and/or work-around it.
If possible, change your application to use the standard port, 5684.
Modify the Wireshark COAP dissector to also register to the DTLS dissector with your desired port, or better yet to allow the port to be configurable, perhaps even with a port range preference to allow multiple ports to be registered. You can reference the Wireshark Developer's Guide for information about compiling and developing for Wireshark on your particular platform.
Submit a Wireshark Issue, asking for an enhancement to the COAP dissector to allow the DTLS-registered port to be configurable. Again, a range preference would probably be even better, as it would allow more than just 1 port to be registered.
Assuming the first option isn't possible and the other options would take longer and not solve the immediate problem of dissecting the payload as COAP for your existing capture file, you could use a program such as TraceWrangler (or other such Capture file editors and/or anonymizers tools) to rewrite the UDP port value of 57845 to 5684 for all packets. That should allow the payload to be passed to the COAP dissector without requiring any other changes. If you do use TraceWrangler, then the basic steps would be:
Add Files: Choose your file, i.e., file.pcapng.
Taskname: Anonymize Files.
Payload: Deselect "Remove all unknown layers..." as you want to keep everything.
PCAPng: Action=Passthrough, as there's no need to replace original comments here.
Layer 4, UDP: Action=Replace. Select "Replace UDP ports by list", then choose Add. Enter 57845 for the Original port number and 5684 for the Replacement port number, then click Add.
Select Okay.
Select Run.
When the Status indicates, "Task complete", you should be able to open the newly created packet capture file, named file_anon.pcapng, in Wireshark and Wireshark should now recognize the payload as COAP.
DISCLAIMER: I have not tested this myself, but it should work.
I am new to GNU Radio and Linux.
I want to send processed data out from gnu companion to a software/dashboard whose input is LAN/TCP/IP.
I am using RTL dongle and USRP and i have done GMSK demodulation successfully.Now want to send the demodulated data to a software for presentation and display developed by another team.The dashboard/software uses Ethernet data as input and has ip address and port as input parameters.
Currently i failed to send a random data via TCP sink and receive it via TCP source blocks on loopback address.
Please help me
Did you set the TCP Sink to "Server", and the Source Block to "Client"? Only the block that is set to "Client" needs to know the address, but both need to know the Port.
And is the port you use for your loopback test free, or could another program be using it?
Also, if the Nonblocking mode for the TCP blocks is off, the execution of the flowgraph is halted until a connection is established. I’m not sure but I think that could lead to problems if they are supposed to connect to each other in the same flowgraph.
Try using an external program (like netcat) for debugging instead. netcat will probably not display it correctly but it’ll tell you if any data at all is coming through.
Additionally, the TCP source and TCP sink blocks are deprecated and shouldn’t be used, use UDP or ZeroMQ for communicating with external programs instead, if possible.
I have a great confusion about tshark.
What is the basic unit of the messages captured by tshark? Ip, tcp, or http?
I see TCP http or ssl and so on in the protocol column in wireshark.
These protocols are in different layer.
In addition, what is the tshark command to capturing the http message with tshark.
See the man page. To quote:
TShark is a network protocol analyzer. It lets you capture packet data from a live network, or read packets from a previously saved capture file
Packets are usually either TCP or UDP (you can find a list of protocols here), When wireshark states that it is HTTP or SSL, then it is based on introspection of the packet (Probably based on destination port).
I am working with a "real time" data analysis toolchain which is separated into two parts. The first part fetches the data to be analyzed, packs it into a UDP packet and sends it to another host. The second part, running on the aforementioned host, receives the UDP packets and performs analysis on the received packets. By "real time" I mean that the output of the analysis toolchain should appear live to a human user, thus latencies of up to 100 ms are acceptable.
I am looking into making a new data source available to the receiving part. The data that I am looking for are being transferred on an Ethercat bus, which I can sniff. Wireshark/tshark have a dissector for Ethercat packets. With that said, it's really simple to get at the data in a script running within Wireshark/tshark. Since I have little control over the second part of the analysis, I cannot readily modify the second part to sniff Ethercat frames via pcap or somesuch.
Is it possible to send UDP packets from a script running in Wireshark/tshark?
Wireshark's Lua doesn't have a way to do that available out-of-the-box, but it's stock Lua so you can write a wireshark Lua script which itself can import (i.e., use require) any other Lua script or compiled Lua dll/so library. So, for example, you could use the LuaSocket library to send packets from within your wireshark Lua script.
Note that there is no event loop available to Wireshark Lua scripts, so receiving packets via LuaSocket isn't going to work, afaik. But since you're talking about sending over UDP, and sending only when the Wireshark Lua script will get invoked (i.e., because you'd do the send() call inside a tap or dissector), I think it should work. If it does/doesn't please post back, because this question comes up now and then and it would be good to know.
Hey SO,
What examples do you know - of protocols initially "handshaking" in UDP, then "conversing" in TCP.
I know there are heaps, I just can't seem to think of any right now.
Specifically, I'm trying to write a Wireshark dissector - for this kind of protocol.
So being able to peek on a similar dissector, seems like a good start.
Would love to hear if you've ever written a stateful Wireshark dissector in LUA.
One example is SIP/Fax.
SIP/SDP setups the session for fax transmission, and then transfers fax/image via TCP/TPKT.
There are several that use both UDP and TCP (see Apple's list, marked as TCP/UDP), but I don't know if they behave exactly as you've described (initial handshake with UDP). DNS and NFS are a couple examples.
I've written Wireshark dissectors in Lua, but not stateful ones.
Surely a handshake would be in TCP being a stateful connection? A handshake seems like something that would want to be ordered, compared to UDP where there is stateless transmission?
I've added some kind of statefulness for the HTTP protocol within my project aimed to lookup original HTTP request for given HTTP response.
Generally speaking, Lua has nice notion of closures which can be used as kind of static global variables for holding handshakes and whatever other references.