Is there some way to get the Frame Check Sequence (FCS) from an ethernet frame when using Wireshark to capture packets under Linux?
The FCS is generated by the sender's ethernet device and decoded by the recipients ethernet device. If the FCS is correct, the payload is passed up to higher layers. If it's not, then the potential frame is discarded.
Because it's added for the exclusive use of the ethernet layer, there's no reason to pass the data up to the operating system. There's no reason for the hardware to include additional capabilities of moving that data out of the card. All modern ethernet devices do onboard FCS processing (and often much more). The only exception would be devices intended to analyze ethernet performance and function.
The Ethernet wiki page on Wireshark states:
Most Ethernet interfaces also either don't supply the FCS to Wireshark or other applications
so I assume the answer is a no.
Related
What is the use of packet boundary flag in L2CAP in Bluetooth.
And it also has concept of automatically Flushable, Non-automatically Flushable and Point-to-point. What does it mean?
Please answer the question, It would be great help.
Thank you in advance
The packet boundary flag is part of the fragmentation and reassembly mechanism which allows L2CAP to transfer data units that are larger than the payload in the physical packets sent over the air.
I suggest you read about the HCI ACL data packet format, you can find it in the Bluetooth core specification which is freely available from the Bluetooth SIG website https://www.bluetooth.com/specifications/specs/core-specification/
Can some expert please throw some light on what is knet interface and what is it used for.
One of my container images show knet2 as an interface for output of 'ifconfig'
I have no idea what it is, can someone please explain or point me to documents / web where I can find more about it.
knet is kernel network interface for efficient of packet exchange between switch and the kernel (linux operating system) network protocol stack.
There could be other methods which could used, such as implementing a software connector module over the Open NSL Rx/TX APIs.
The intent of theknet interface is to provide a network interface that
then delivers packets to the NetIO framework from the kernel.
this is nicely explained in user-networking.pdf.
I hope this is what you were expecting. feel free to comment for any clarification.
this is about knet reference
This module implements a Linux network driver for Broadcom
XGS switch devices. The driver simultaneously serves a
number of vitual Linux network devices and a Tx/Rx API
implemented in user space.
Packets received from the switch device are sent to either
a virtual Linux network device or the user mode Rx API
based on a set of packet filters.susp
Packets from the virtual Linux network devices and the user
mode Tx API are multiplexed with priority given to the Tx API
I'm developing a high-speed USB peripheral and using Wireshark to sniff the USB traffic. In Wireshark, each line displayed corresponds to a single URB.
Because I'm developing on the device side, I don't really care about URBs, instead, I'd like to see individual packets.
For instance, during a single control transfer, this is what I see in Wireshark:
But this one control transfer consists of 9 packets in the following sequence:
{{SETUP, DATA0, ACK}, {IN, DATAx, ACK}, {OUT, ZLP, ACK}}
Can I see the exact timing and contents of each of these packets, or is that something that I would need to buy a hardware USB analyzer for?
My operating system is vanilla Ubuntu 16.04
Recently I encountered several questions on SO regarding working with sockets on a very low level. Here's an example. While looking for an answer, I realised that sockets have relatively low capabilities on OSI Level 2. On Linux, we can specify a protocol when creating a socket, but obviously not all Level 2 protocols are present in the list.
While it is possible to assemble and send an ethernet frame, it's (presumably) not possible to send a 802.11 packet - though it looks like wifi device drivers do convert ethernet frames to wifi packets and vice versa.
This made me wonder, if there are more possibilities in reading and writing directly to device files like eht0, ath0? Is it a socket implementation who usually writes to these files, or a device driver? And who's on receiving side - a NIC driver, a peripheral bus controller?
I'm new on work with linux. I want capture the ethernet packets above the device drivers layer.
I know that all the packets pass through the functions "dev_queue_xmit" to transmit the packet to the upper layer and the function "netfi_rx" for recieving the packet.
How can i "hook" this function to control the ethernet traffic?
what should i work with to accomplish this task?
You might want to check out libpcap (a portable C/C++ library for network traffic capture). There is also an example.
You might want to use raw sockets. http://aschauf.landshut.org/fh/linux/udp_vs_raw/ch01s03.html
See also this question