TL;DR available at the bottom
I've been trying to figure out a way to get two laptops (both running Ubuntu) to be able to pass basic messages back and forth without the need for them to be connected via a wireless network,either by an AP or ad-hoc. I want to reiterate here that ad-hoc networking is not what I'm looking for, I've seen many similar questions here with that as the answer.
I guess what I'm asking is: how do I achieve this? All I really need is for one computer to be able to send a packet, and then for another to pick it up via a packet sniffer of some kind.
Currently: I have both laptops in monitor mode (via a mon0 interface created from aircrack-ng's airmon-ng)so that they can sniff nearby traffic (with Wireshark, tcpdump,tcpcump.org's sample libpcap code, and opening a raw socket and just printing out all the packets. I tried each just because I thought one could be doing something differently/leaving something out). I also have a very basic program that consists of opening a raw socket to send crafted ethernet frames out to the air, but I can't get my two machines to see the other's packets. The sniffer running on each machine can only see the packets going out of that machine (in addition to nearby beacons/control traffic from wifi in the area).
Some things to note that might be important are:
-the packets I'm sending out appear in Wireshark (only on the sending machine) as malformed 802.11 packets (probably because I'm just filling them with junk data for now). I was under the impression that my other laptop would also see them as malformed packets, but it gets nothing
-the sockets I'm using are from a call to socket(PF_PACKET,SOCK_RAW,ETH_P_ALL). Raw sockets are something I just recently was aware of, so I could be misunderstanding how they work, but my impression is that I can craft a layer 2 packet by hand and ship out straight out to the wire/air.
If you're curious as to why I want to do something like this, it's part curiosity, part research for a project I'm working on. I want to streamline / automate the process of setting up an ad-hoc network, and what I'm trying to do here is for the laptops to do a small exchange to figure out the specifics of the adhoc network they are about to create and then make/join that network automatically, instead of either one person explicitly setting up the network OR having both people pre-decide the name, etc of the network and have both computers constantly trying to connect to that specific one.
I'm more interested if I'm going about this process in the right way rather than if my code works or not, if someone thinks me posting my (very basic, taken from another post on Stack Overflow) raw socket code will help, I can.
Edit: I am more than happy to post a complete set of code with instructions if I can get this working. I couldn't find much helpful info on this topic on the internet, and I'd love to put it up for future people trying to do the same thing.
TL;DR I want to send out a packet from one laptop and pick it up on another via a packent sniffer of some sort. No wifi network or ad-hoc network involved. Something akin to spoofing an AP's beacon frame (or similar) for the purpose of sending small amounts of data.
Edit 2:After some thought, perhaps what I'm looking for is some kind of raw 802.11 use? Having direct control of the wifi radio? Is such a thing possible?
I found out I was able to send packets out through my monitor mode interface as long as I had correct 802.11 with radiotap headers. I think the problem I was originally experiencing (not being able to sniff the packets) was because they were malformed and thus not actually getting sent out.
I was able to accomplish this by adapting the example code found here, courtesy of someone named Evan Jones, except I did not need to use an Atheros based card or Madwifi drivers, everything worked fine with the mon0 interface created with aircrack-ng.
I am certain that Apple Mac do this. Apple call it 'bonjour'. There may well be a proper IETF spec for it. This is an Article on Bonjour this is Wikipedia on an open component of bonjour which might help get you moving.
Related
I have an obsolete hardware level/pressure transmitter that communicate with mcu using custom protocol (it appear to be similar to modbus RTU), that hardware comes along with an old commissioning software that works perfectly fine under latest windows, that software contain all communication protocol components that I try to extract and use in something like Arduino to pull data out of transmitter, anyone can help out?
Update - Didn't mentioned above that form of communication here is half-duplex serial communication where master hardware/software query slave transmitter.
Now mentioned to program Arduino mcu to pool data out of transmitter.
What best way of getting readable data out of it?
Again many thanks for all your comments and help!
What you need is called a sniffer. Use that as a keyword and you should be able to find plenty of info here at SO and around the web.
To set the record straight it is actually possible to use Wireshark to sniff on Modbus RTU over serial, see my answer here. If your protocol is similar to Modbus I would start with SerialPCAP.
If you prefer more Windows-friendly solutions you can check these out: 1, 2.
Since Modbus is pretty simple I would say reverse engineering a similar protocol should be, maybe not a piece of cake but just manageable, even if you are not very experienced.
These days when almost everyone is a maker or at least a wannabe, you might want to first take a good look around, maybe somebody else already reverse-engineered that protocol and published it somewhere.
The best tool to analyze a protocol is Wireshark. Run it on the communication link between the Windows machine and the radar. First possibility: the protocol is actually something that Wireshark knows (some trials and errors with the "Decode as" menu may be necessary.) Second possibility, less funny: the protocol is indeed completely proprietary and unknown to Wireshark. At least, Wireshark will make it easier to examine the binary data.
Is there a way to view all the IPv4 packets sent to a Linux computer?
I know I can capture the packets at the ethernet level using libpcap. This can work, but I don't really want to defragment the IPv4 packets. Does libpcap provide this functionality and I'm just missing it?
One thing that kinda works is using a tun device. I can capture all the IPv4 traffic by routing all traffic to the tun device via something like ip route add default via $TUN_IP dev $TUNID. This also stops outbound traffic though, which is not what I want.
I just want to see the IPv4 packets, not intercept them. (Or, even better, optionally intercept them.)
Edit: I'm specifically looking for a programmatic interface to do this. E.g. something I can use from within a C program.
Yes, you can see all the packets that arrive at your network interface. There are several options to access or view them. Here a small list of possible solutions, where the first one is the easiest and the last one the hardest to utilize:
Wireshark
I'd say this is pretty much the standard when it comes to protocol analyzers with a GUI (uses libpcap). It has tons of options, a nice GUI, great filtering capabilities and reassembles IP datagrams. It uses libpcap and can also show the raw ethernet frame data. For example it allows you to see layer 2 packets like ARP. Furthermore you can capture the complete data arriving at your network interface in a file that can later be analyzed (also in Wireshark).
tcpdump
Very powerful, similar features like Wireshark but a command line utility, which also uses libpcap. Can also capture/dump the complete interface traffic to a file. You can view the dumped data in Wireshark since the format is compatible.
ngrep
This is known as the "network grep" and is similar to tcpdump but supports regular expressions (regex) to filter the payload data. It allows to save captured data in the file format supported by Wireshark and tcpdump (also uses libpcap).
libnids
Quotation from the official git repository:
"Libnids is a library that provides a functionality of one of NIDS
(Network Intrusion Detection System) components, namely E-component. It means
that libnids code watches all local network traffic [...] and provides convenient information on them to
analyzing modules of NIDS. Libnids performs:
assembly of TCP segments into TCP streams
IP defragmentation
TCP port scan detection"
libpcap
Of course you can also write your own programs by using the library directly. Needless to say, this requires more efforts.
Raw or Packet Sockets
In case you want to do all the dirty work yourself, this is the low level option, which of course also allows you to do everything you want. The tools listed above use them as a common basis. Raw sockets operate on OSI layer 3 and packet sockets on layer 2.
Note: This is not meant to be a complete list of available tools or options. I'm sure there are much more but these are the most common ones I can think of.
Technically you have to make a copy of the received packet via libpcap. To be more specific, what you can do is to get packets with libpcap, that way the packets will be kind of blocked, so you need to re send them to the destination. Lets say that you want to make a Fire-Wall or something, what you should do is to have a layer that can work like getting the package and then send it to the destination, in between you can make a copy of what you got for further processes. In order to make the intercept option, you need to create some predefined rules, i.e. the ones that violates the rules will not be send again to their destination.
But that needs a lot of efforts and I don't think you want to waist your life on it.
Wire-shark as mentioned by #Barmar can do the job already.
If you need some kind of command line interface option I would say that "tcpdump" is one of the best monitoring tools. for example for capturing all ipv4 HTTP packets to and from port 80 the command will be:
tcpdump 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
for more information and options see tcpdump
Please be specific if you need to write a program for it, then we can help about how to do it.
This may not be in the right location, so tell me and I'll move it.
I am a recent EE grad and I was hired to build a system that exists on a SoC with a simple 32-bit processor. The system basically monitors several external devices and performs some DSP on it, and then is supposed to send the results using a WiFi device (in my case I have the ESP8266 using UDP) to an email server for logging/notification.
I have been trying to find a library that I can use, but my uC can only program in C and I have it set up for UDP, and everything is in C++ using some other protocol, or something else completely.
I am great at DSP, decent at SoC's and uC's, but when it come to this email server communication thing I am at a loss.
I have successfully configured everything for the sensors, the datapath, the DSP, and connected the system to my WiFi via UDP, but I have yet to figure out how to send data to any servers.
Could someone help me understand how I should go about this?
I have looked into some simple SMTP commands such as HELO, MAIL, RCPT, DATA, etc. but I cannot understand how I actually should implement them in my code.
When I send out the WiFi data via UDP what type of data do I send and how do I format it? Do I need to send any other kind of flags? How should I expect the response? I also know the data has to be transformed into base 64 which is confusing me further.
I am also not super familiar with UDP to begin with, I have been using libraries that are part of the SoC's default library to connect to my WiFi.
I know these may either seem like obvious or stupid questions but it is were I no longer have any knowledge, and everything I find online doesn't make sense, or doesn't attempt to explain it, just gives a pre-made solution
I have found the RFC2821 but it doesn't get any clearer.
I know that's a lot but any help at all would be a lifesaver!
Since you are asking this question, I'm assuming that you are not booting and running an OS suitable for micro-controllers such as an embedded variant of Linux or such. If you were, you would simply be able to take advantage of possibly built in applications or other existing code.
But you don't mention having written an Ethernet stack, so are you using some other library or operating environment which might have some of the functionality needed for an implementation of SMTP?
If you don't and really do need to write your own SMTP client to run directly on the processor you are using, then you should be able to find plenty of examples of source code for this. A quick google search of How To Write an SMTP client showed a few articles with some example code. One article seems to be an exact hit, but you need to look at it further.
However, I would highly suggest just sitting down with a telnet client and connect to an SMTP server you are allowed to use and try the commands you need to just send a message. If you only need to send text, you don't need to get involved in MIME encoding or anything like that.
I am trying to create a client in C that will talk with a BACnet server. This BACnet server is stored on an industrial device (CAN2GO) and I am not sure how I could talk with this device.
I spent quite some time reading documentation for BACnet and I never found a clear example for a BACnet client. I already did some server and clients using TCP and UDP but I don't know how to start this BACnet client and I must say I am getting quite desperate.
I found a library which seems to correspond to what I want which is called BACnet protocol stack but when I tried the whois exemple no device was found (I expected to found the bacnet server but maybe I shouldn't ?).
So my question is : could you give me an exemple in C, or another language but C would be better, that would communicate with a BACnet server (nothing complicated just a question and analysing response). This example could be using the library I just wrote about or if you prefer another library I am of course open to everything.
Thank you very much for your time and answers.
I have used that stack and it is the best open source one you are going to find. If you cannot see anything using the demo\whois\bacwi example from that library, then there is something wrong with your setup. In particular, are you using IP? Are your BACnet client and BACnet server on different machines (they cannot be on the same without some serious tweaking)? Are the two machines on the same IP subnet? (They must be, once again, unless you do some serious tweaking (in this case, setting up BBMDs (BACnet Broadcast Management Devices))).
You will also want to try the "Read Property" example (demo\readprop\bacrp.exe) to actually read a value from the server.
If you are still stuck, then post your detailed problem at the link on Sourceforge, Steve, the author, is very responsive to questions.
I am currently using the stack - just started. I had a little trouble at first, not sure if my problem is the same but.. I basically am using some BAC components made from Schneider Electric (UNC-500) and an old un-supported platform (Niagara R2). On my laptop I created a host server and addressed it to a private LAN network between it and the UNC. My laptop was also using wifi, which was utilizing DHCP, so I had two separate interfaces going. This was my problem. I couldn't read or get 'I-AM' responses back from the UNC. As soon as I turned the WIFI off, I got the 'I-AM' broadcasts. Make sure that you are on the same network as your device, and that there are not other interfaces active. Maybe there is a way to assign the interface to use, IDK. I just started using it.
is it possible to capture some packets in promiscuous mode (e.g. using winpcap) and than force OS (applications) to receive them as they were sent for our MAC?
My observation is following. We can:
capture all network traffic using
promiscuous mode (winpcap)
filter/modify the packets using
firewall-hook/filter-hook
send packets to the network with altered MAC
I am not sure if firewall-hook can access all the packets which are available thanks to promiscious mode. Isn't it on the lower layer? If it can't, the only solution would be to capture desired packets and then resend them to the network with altered MAC?
I am networking novice so please be easy on me :)
Any help is appreciated.
Thanks in advance.
You have your toes at the line of white hat/black hat hackers. I know that my company actively watches for promiscuous NICs, hunts down the owners and kills (fires) them. Maybe if you ask us what you're trying to do, we can offer some suggestions.
If you're trying to analyze your network, there is software and/or hardware solutions that will probably do a better job. If you're just trying to watch interesting text flow across your network, well ... maybe you're still in college.
First, yes if your interface operates in promiscuous mode then you will receive everything 'on the wire'. Which is already one difficulty, nowadays many (if not all) networks are switched, which means a piece of hardware exterior to your system will already do some filtering before packets arrive at your system, so you'll first need to trick a switch into transmitting those packets to your end (can be done by sending out dummy arps, by configuring the switch, or by bad intent ;-) ).
Then if these packets receive at your system, what do you plan to do with them ? There ethernet frames will carry ip packets, typically with a destination ip address, which is already something which will not be on your host (and if it is, this implies that you will have duplicate ip addresses on your network, causing problems as well.
So the main question is, what do you really really really want to do ?
Once you have recieved a packet, it has already been clean through the protocol stack. I don't think Windows gives you the access into the middle of Winsock that would be required to somehow stick it back in.
More importantly, this is a really dodgy think to be looking to do. Whatever it is you are looking to do, I can guarantee you there is some better way to do it.