I am trying to create pcap filter for filtering ARP replies only. In wireshark i use
arp.opcode==2
and it works perfectly. But when i use it in pcap_compile function, it throws an exception - syntax error. I tried also these variants:
arp.opcode = 2
arp.opcode 2
arp opcode 2
arp.reply
arp reply
and nothing seems to work. I tried to google it, but no success. Is it even possibly to filter that specific packets?
I suspect this should work, based on the packet structure from Wikipedia:
arp [6:2] = 2
That's also suggested by this answer: https://stackoverflow.com/a/40199540/212870
(It's easier to look up once you figure out the answer, unfortunately.)
Related
I'm trying to transmit messages through CAN using HAL library. For test I repeated code from the first part of this video I have the same bluepill so I just did the same. Also I've tried his project, but changing Nucleo RE to ZE model. I've looked through other sources and they all do the same thing, and in their videos/articles bus perfoms as it is supposed to.
But on all of my devices HAL_CAN_AddTxMessage produces empty (or maybe error) message
Theese different lines are TX on one board and RX from other transcievers.
Debugging showed me nothing wrong: function returns HAL_OK. I went step by stem through it in debug mode and everything seemed as normal. But niether loopback nor normal mode transmitts correct message.
Also I've checked my LA with MCP2515 + TJA1040 and CAN bus worked as it has to
So I'm confused and don't understand what I'm doing wrong.
The problem was in TimeQuanta settings. I had to be more considerate. I'll wrigth a more exact explanation later
We are parsing pcap files that are created via the tcpdump command. Inside these pcap files we are attempting to extract the GET request information in the Raw field and print it in a readable format.
pkts = rdpcap(filename)
for pkt in pkts:
if Raw in pkt:
raw_test = pkt[Raw].load
if "GET" in raw_test:
#do stuff
The resulting text of raw_test comes out looking like this:
▒פ▒▒▒▒▒▒2▒nk▒N▒▒bEr▒▒(|▒▒▒▒Ǫ=▒▒Ih▒H+%▒2.▒L[▒▒▒sl▒E▒▒▒k6▒]=މf▒d▒O▒hB{6s▒▒▒7O2!PCG&▒A.4I▒耓▒X▒▒▒W]▒▒M5#▒▒▒vK▒#Ċ▒ ▒▒▒m]Zb_▒8▒▒▒nb~
]▒h▒6▒.̠▒49ؾG?▒▒▒4▒Ӹ▒▒G▒▒́G▒:Y▒▒▒▒.▒8▒▒d▒i4▒JAC)▒▒AO▒k▒z-▒▒S30▒X?▒▒W5B▒yW▒m▒▒▒/ƈ:G▒▒▒E▒▒<▒▒▒m▒]▒▒▒▒t▒:▒▒▒Ŕ▒W▒▒D▒E▒▒▒▒▒࿄▒▒zZ▒▒x▒]▒▒{{▒▒u▒){▒▒o▒▒G▒F▒▒▒▒▒v
▒▒▒b.
We have also tried formatting it via pkt.sprintf(“{Raw:%Raw.load%}\n”) but that has yielded the same output
P.S. Please do not link us to other related stack posts/questions as we have come across many of them already, and none of them seem to fix our problem.
Thank you in advance, any help is greatly appreciated!.
Please try this, I assume that http is targeted to port 80
if TCP in pkt and pkt[TCP].dport == 80 \
and pkt[TCP].load.startswith("GET") :
print pkt[TCP].load
I have a python script which assembles and sends AVB (IEEE) packets into a network.
The packets will be captured by wireshark.
With an other python script I iterate through the capture file.
But I can't access a few parameters in a few layers because scapy doesn't know them.
So I have to add those layers to scapy.
Here's the packet in wireshark:
I added the following code to the file "python2.7/dist-packages/scapy/layers/l2.py"
class ieee(Packet):
name = "IEEE 1722 Packet"
fields_desc=[ XByteField("subtype", 0x00),
XByteField("svfield", 0x81),
XByteField("verfield", 0x81)]
bind_layers(Dot1Q, ieee1722, type=0x22f0)
When I execute the python script which should grab the parameters in the new layer (IEEE 1722 Protocol), the following error occurs:
"IndexError: Layer [ieee1722] not found"
What's wrong?
Ok, found the solution by editing the type value:
bind_layers(Dot1Q, ieee1722, type=0x88f7) ---> works
Dot1Q is the layer above the created ieee1722 layer (see wireshark).
You can see the type value by clicking at the layer of a packet in wireshark.
This is old, maybe they didn't have the doc page but they have it now:
"Adding new protocols"
https://scapy.readthedocs.io/en/latest/build_dissect.html
Using wireshark, I could see the html page I was requesting (segment reconstruction). I was not able to use pyshark to do this task, so I turned around to scapy. Using scapy and sniffing wlan0, I am able to print request headers with this code:
from scapy.all import *
def http_header(packet):
http_packet=str(packet)
if http_packet.find('GET'):
return GET_print(packet)
def GET_print(packet1):
ret = packet1.sprintf("{Raw:%Raw.load%}\n")
return ret
sniff(iface='wlan0', prn=http_header, filter="tcp port 80")
Now, I wish to be able to reconstruct the full request to find images and print the html page requested.
What you are searching for is
IP Packet defragmentation
TCP Stream reassembly
see here
scapy
provides best effort ip.defragmentation via defragment([list_of_packets,]) but does not provide generic tcp stream reassembly. Anyway, here's a very basic TCPStreamReassembler that may work for your usecase but operates on the invalid assumption that a consecutive stream will be split into segments of the max segment size (mss). It will concat segments == mss until a segment < mss is found. it will then spit out a reassembled TCP packet with the full payload.
Note TCP Stream Reassembly is not trivial as you have to take care of Retransmissions, Ordering, ACKs, ...
tshark
according to this answer tshark has a command-line option equivalent to wiresharks "follow tcp stream" that takes a pcap and creates multiple output files for all the tcp sessions/"conversations"
since it looks like pyshark is only an interface to the tshark binary it should be pretty straight forward to implement that functionality if it is not already implemented.
With Scapy 2.4.3+, you can use
sniff([...], session=TCPSession)
to reconstruct the HTTP packets
Working on parsing Arp packets and I found this nice problem.
when receiving an Arp packet I was parsing the target's IP address.
I have c0 a8 in my hex dumb but after that it ends. I am missing data! I see the data in Wireshark but I am not getting the data through WinPCap.
I have yet to run into this issue before. Any ideas SO? So far no memory access errors though. Probably just luck. :x
EDIT:
My main look for processing packets is from the example pktdump_ex.
Here is the while line
while((res = pcap_next_ex( fp, &header, &pkt_data)) >= 0)
After that is executed, the snalen is 2b.
As noted in he comment, this smells like a faulty snaplen configuration. If you look at the winpcap api docs pcap_open() apidoc, it states:
snaplen,: length of the packet that has to be retained. For each packet received by the filter, only the first 'snaplen' bytes are stored in the buffer and passed to the user application. For instance, snaplen equal to 100 means that only the first 100 bytes of each packet are stored.
As explanation for the second parameter of pcap_open. Unless you provide some more detailed code snippets to work with, this is the closest to an answer we will get.