nRF Sniffer integration for 802.15.4 in a python scipt (Pcap file problems)

[Ayoub GH]

I have developed a python script to sniff the OpenThread network using the Nrf802154Sniffer() library, which generates a pcap file.

 I used it with the nRF Sniffer hardware (nRF52840 DK and nRF52840 Dongle).

The problem is that in the pcap file generated, I found that there are packets that are not well analyzed, but in Wireshark it sniffs packets well.

Do you have any idea where this problem comes from.

thank you in advance

Best regards,

Ayoub GH

[Øyvind]

Hello, 

I'm not sure I understand the question. Can you please elaborate more on what you are trying to achieve?

Thank you.

Kind regards,
Øyvind

[Ayoub GH]

the problem is that when I sniff with a python script, the packets are not well analyzed. but when I use Wireshark the packets are well captured.

Attached is the screenshot of the Pcap file generated with the python script and the Wireshark capture.

in the attached photo the colored lines (orange, blue, green) in the python script should be like the colored lines in Wireshark.

We also note that the time corresponds well to what is captured by Wireshark, but the capture stops in the IEEE 802.15.4 layer instead of going to the CoAP layer

Note: the sniff with python and with Wireshark are launched at the same time

[Øyvind]

I've forwarded these to one of our WireShark experts. He replies that it works for him. What version of Wireshark are you running?

Here is the "failed" file at his end. Note that without encryption key, it is not possible to see CoAP content:

[Ayoub GH]

I use Wireshark version 3.4.6

For the encryption key here is the screenshot:

Best regards,

Ayoub GH

[Øyvind]

Our experts is not able to reproduce and answers that it looks good to him. Looking at the pcap file, he does not suspect an issue with the python script either. 

[Stig]

In Pcap_Failed you are missing a 802.15.4 Broadcast packet with full source address to be able to recreate the "Extended Address" (needed for decryption) on packets without full source address. You can see this in "Source Address Mode" Long vs. Short in the 802.15.4 Frame Control Field, and the following "No extended source address - can't decrypt" warning from Wireshark. In working packets you will find a "Origin" field with a reference to this Broadcast packet.

In Pcap_Passed you have several of this packets in the beginning.

In the attached Pcap_Failed_Fixed I have manually copied packet 6 to the beginning of the file, and then the decryption should work.

Pcap_Failed_Fixed.pcap

[Ayoub GH]

I thank you for your answer and for all this very useful information, it allowed me to understand well the problem of the sniffer.

I have two other questions to ask you about this problem:
- Why does it sometimes work very well and I have no problem decrypting package with python sniffer ?

- Since it seems it's a problem of configuration of sub layers (Coap, 6LowPan, IPv6, IEEE 802.15.4 ...) in my python script, is there a way to configure the sniffer in Python? At the moment, I only use extcap_capture function, however in wireshark, I followed the explainations in the folowing documentation :
infocenter.nordicsemi.com/.../nRF_Sniffer_802154_User_Guide_v0.7.2.pdf

Whould you know the needed function to do a correct configuration with Python librarires?

Best regards,

Ayoub GH