LoRaWan PCAP, wireshark not able to interpret

asked 2019-09-05 12:43:03 +0000

apku04
1 ●1 ●1 ●1

having trouble getting wireshark to open my pcap file. I have wireshark 3.0.3, installed and I am using LoRaWan tap as defined here: https://github.com/eriknl/LoRaTap

my pcap header looks like this:

pcap_header[0] = 0xa1; //PCAPH_MAGIC_NUM
pcap_header[1] = 0xb2; //PCAPH_MAGIC_NUM
pcap_header[2] = 0xc3; //PCAPH_MAGIC_NUM
pcap_header[3] = 0xd4; //PCAPH_MAGIC_NUM
pcap_header[4] = 0x03; // PCAPH_VER_MAJOR
pcap_header[5] = 0x00; // PCAPH_VER_MINOR
pcap_header[6] = 0x00; // PCAPH_THISZONE
pcap_header[7] = 0x00; // PCAPH_SIGFIGS
pcap_header[8] = 0xFF; // //PCAPH_SNAPLEN_1
pcap_header[9] = 0xFF; // //PCAPH_SNAPLEN_1
pcap_header[10] = 0x01; // LORATAB1
pcap_header[11] = 0x0E; // LORATAB2

my loraTap header looks like this:

loratap_header.lt_length = sizeof(loratap_header);
loratap_header.lt_version = 0;
loratap_header.channel.bandwidth = 125000;
loratap_header.channel.frequency = p->freq_hz;
loratap_header.channel.sf = p->datarate;
loratap_header.lt_padding = 0;
loratap_header.rssi.current_rssi = p->rssi;
loratap_header.rssi.max_rssi = p->rssi;
loratap_header.rssi.snr = p->snr;
loratap_header.rssi.packet_rssi = p->rssi;
loratap_header.sync_word = 0x34;

when I receive a LoRa frame I create a "loratap_header" as specified from "Eriknl, git" and dump the frame after it. everything is dumped to a xxxx.pcap by "fwrite(...)" in C code

when I open the pcap i get the following error

"The file "The file "log_trace.pcap" contains record data that Wireshark doesn't support. (pcap: network type 1208090624 unknown or unsupported)"

any idea of this error? wireshar should support LoRawan according to https://www.wireshark.org/docs/dfref/...

answered 2019-09-05 14:04:58 +0000

Pascal Quantin
5831 ●63 ●65

Hi,

your libpcap header format seems wrong (for example fields like major and minor versions are 2 bytes long, not 1, the network type is 4 bytes long and not 2 bytes long, etc...). Please refer to https://wiki.wireshark.org/Developmen... for a description of the format, and pay attention to fields that are more than 1 byte long (guint16, guint32...): you should write them properly so that Wireshark can guess your machine endianness.

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your libpcap header format seems wrong

That's because it IS wrong, for the reasons you specify.

Please refer to https://wiki.wireshark.org/Developmen... for a description of the format

Or to the closest thing to an official specification, namely either the text version or the HTML version of the pcap-savefile(5) man page. (One of these days there should be a specification in I-D format, and maybe it should even become an RFC, just as there's an RFC for the Sun snoop capture format.

Guy Harris ( 2019-09-05 19:15:40 +0000 )edit

I thank both for your input,

I have one question thou; I can see that the file should include:

pcap_hdr
pcaprec_hdr raw_data ....

but what about the pcaptap_hdr as mentioned here: https://github.com/eriknl/LoRaTap

I thought that the pcaptap_hdr should accompany each rawdata frame and not the pcaprec_hdr as mentioned in those spec you both provided ?

or is it

[pcap_hdr] [pcaprec_hdr] [pcaptap_hdr] [raw_data] ....... [pcaprec_hdr] [pcaptap_hdr] [raw_data] .. and so on ?

apku04 ( 2019-09-06 05:43:11 +0000 )edit

At the beginning of your file you should have a pcap_hdr_t structure. Then for each packet you should have a pcaprec_hdr_t structure followed by the loratap_header_t structure and the raw data. So a pcap with 2 packets should look like this:

[pcap_hdr_t][pcaprec_hdr_t][loratap_header_t][raw_data][pcaprec_hdr_t][loratap_header_t][raw_data]

Pascal Quantin ( 2019-09-06 07:23:32 +0000 )edit

I.e., pcaprec_hdr_t is the format of the header that is at the beginning of every single record in every single pcap file, regardless of the link-layer type.

What follows each pcaprec_hdr_t is a link-layer header of the type described, for the link-layer type in the file, in the list of link-layer header types for pcap and pcapng files. For LINKTYPE_LORATAP (270), that page says what follows the pcaprec_hdr_t is a LoRaTap header. After that comes whatever follows that.

Guy Harris ( 2019-09-06 07:37:01 +0000 )edit

got it working now thanks both :)

apku04 ( 2019-09-06 08:02:45 +0000 )edit

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