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I have PcapNG files created by Wireshark, which I try to parse with python-pcapng.

However, I cannot figure out how to reconcile the output I receive from FileScanner's packet_payload_info with the 802.11 Data frame format:

802.11 Data frame format

This is the output I get (my code is at the bottom):

magic_number 0xa0d0d0a
SectionHeader(version_major=1, version_minor=0, section_length=-1, options=Options({'shb_userappl': [u'Dumpcap 1.12.4 (v1.12.4-0-gb4861da from master-1.12)'], 'shb_os': [u'Mac OS X 10.10.2, build 14C109 (Darwin 14.1.0)']}))

magic_number 0x1
InterfaceDescription(link_type=127, reserved='\x00\x00', snaplen=262144, options=Options({'if_os': [u'Mac OS X 10.10.2, build 14C109 (Darwin 14.1.0)'], 'if_tsresol': [6], 'if_name': [u'en1']}))

magic_number 0x6
EnhancedPacket(interface_id=0, timestamp_high=332139, timestamp_low=2801116064L, packet_payload_info=(45, 45, '\x00\x00\x19\x00o\x08\x00\x00`I\xb2&\x00\x00\x00\x00\x12\x18q\[email protected]\x01\xb1\xaa\x00\xb4\x00\x90\x00\xf4\x0f\x1b\xb8sL`\x92\x175\x00\x01\xe3\xcf\x00\x12'), options=Options({}))

packet_payload_info      : (45, 45, '\x00\x00\x19\x00o\x08\x00\x00`I\xb2&\x00\x00\x00\x00\x12\x18q\[email protected]\x01\xb1\xaa\x00\xb4\x00\x90\x00\xf4\x0f\x1b\xb8sL`\x92\x175\x00\x01\xe3\xcf\x00\x12')

packet_payload_data (hex): 00 00 19 00 6F 08 00 00 60 49 B2 26 00 00 00 00 12 18 71 16 40 01 B1 AA 00 B4 00 90 00 F4 0F 1B B8 73 4C 60 92 17 35 00 01 E3 CF 00 12

packet_payload_data (bin): 00000000 00000000 00011001 00000000 01101111 00001000 00000000 00000000 01100000 01001001 10110010 00100110 00000000 00000000 00000000 00000000 00010010 00011000 01110001 00010110 01000000 00000001 10110001 10101010 00000000 10110100 00000000 10010000 00000000 11110100 00001111 00011011 10111000 01110011 01001100 01100000 10010010 00010111 00110101 00000000 00000001 11100011 11001111 00000000 00010010

Could you tell me where does the packet_payload_data fit in the 802.11 Data frame?*

*i.e., where does its first byte fit in the frame

Python code:

#!/usr/bin/env python

from pcapng import FileScanner

def hex_str_to_num(hex_str,out_format='X'):
    if out_format.upper() == 'B':
        return ' '.join(format(ord(x), out_format).zfill(8) for x in hex_str)
    else:
        return ' '.join(format(ord(x), out_format).zfill(2) for x in hex_str)

PCAPNG = "/cygdrive/c/tmp/LivePerson/lana/trace3.pcapng"
MAX = 3
ENHANCEDPACKET_ID = 6

with open(PCAPNG, "r") as pcapng_file:
    scanner = FileScanner(pcapng_file)
    counter = MAX
    for block in scanner:
        print
        print "magic_number",hex(block.magic_number)
        print block

        if block.magic_number == ENHANCEDPACKET_ID:
            print
            payload_data = block.packet_payload_info[2]
            print "packet_payload_info      :",block.packet_payload_info,"\n"
            print "packet_payload_data (hex):",hex_str_to_num(payload_data,"X"),"\n"
            print "packet_payload_data (bin):",hex_str_to_num(payload_data,"b")

        counter -= 1
        if not counter:
            break

asked 30 Mar '15, 11:06

ronbarak's gravatar image

ronbarak
10225
accept rate: 0%


As indicated by your python library, the link type used for this capture is 127, which means LINKTYPE_IEEE802_11_RADIOTAP (as listed on tcpdump link-layer header type values page). The radiotap format (the one found in your payload data) is specified here.

permanent link

answered 30 Mar '15, 13:10

Pascal%20Quantin's gravatar image

Pascal Quantin
5.5k1060
accept rate: 30%

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question asked: 30 Mar '15, 11:06

question was seen: 2,296 times

last updated: 30 Mar '15, 13:10

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