Related command line tools
<command>text2pcap</command>: Converting ASCII hexdumps to network
captures
There may be some occasions when you wish to convert a hex dump of some
network traffic into a libpcap file.
Text2pcap is a program that reads in an ASCII hex
dump and writes the data described into a libpcap-style capture file.
text2pcap can read hexdumps with multiple packets in them, and build a
capture file of multiple packets. text2pcap is also capable of
generating dummy Ethernet, IP and UDP headers, in order to build fully
processable packet dumps from hexdumps of application-level data only.
Text2pcap understands a hexdump of the form generated by od -t x1. In
other words, each byte is individually displayed and surrounded with a
space. Each line begins with an offset describing the position in the
file. The offset is a hex number (can also be octal - see -o), of
more than two hex digits. Here is a sample dump that text2pcap can
recognize:
000000 00 e0 1e a7 05 6f 00 10 ........
000008 5a a0 b9 12 08 00 46 00 ........
000010 03 68 00 00 00 00 0a 2e ........
000018 ee 33 0f 19 08 7f 0f 19 ........
000020 03 80 94 04 00 00 10 01 ........
000028 16 a2 0a 00 03 50 00 0c ........
000030 01 01 0f 19 03 80 11 01 ........
There is no limit on the width or number of bytes per line. Also the
text dump at the end of the line is ignored. Bytes/hex numbers can be
uppercase or lowercase. Any text before the offset is ignored,
including email forwarding characters '>'. Any lines of text
between the bytestring lines is ignored. The offsets are used to
track the bytes, so offsets must be correct. Any line which has only
bytes without a leading offset is ignored. An offset is recognized
as being a hex number longer than two characters. Any text after the
bytes is ignored (e.g. the character dump). Any hex numbers in this
text are also ignored. An offset of zero is indicative of starting a
new packet, so a single text file with a series of hexdumps can be
converted into a packet capture with multiple packets. Multiple
packets are read in with timestamps differing by one second each.
In general, short of these restrictions, text2pcap is pretty liberal
about reading in hexdumps and has been tested with a variety of mangled
outputs (including being forwarded through email multiple times,
with limited line wrap etc.)
There are a couple of other special features to note. Any line where
the first non-whitespace character is '#' will be ignored as a
comment. Any line beginning with #TEXT2PCAP is a directive and options
can be inserted after this command to be processed by text2pcap.
Currently there are no directives implemented; in the future, these
may be used to give more fine grained control on the dump and the
way it should be processed e.g. timestamps, encapsulation type etc.
Text2pcap also allows the user to read in dumps of application-level
data, by inserting dummy L2, L3 and L4 headers before each packet.
The user can elect to insert Ethernet headers, Ethernet and IP, or
Ethernet, IP and UDP headers before each packet. This allows Wireshark
or any other full-packet decoder to handle these dumps.
Help information available for text2pcap
$ text2pcap.exe -h
Usage: text2pcap.exe [-h] [-d] [-q] [-o h|o] [-l typenum] [-e l3pid] [-i proto]
[-m max-packet] [-u srcp,destp] [-T srcp,destp] [-s srcp,destp,tag]
[-S srcp,destp,tag] [-t timefmt] <input-filename> <output-filename>
where <input-filename> specifies input filename (use - for standard input)
<output-filename> specifies output filename (use - for standard output)
[options] are one or more of the following
-h : Display this help message
-d : Generate detailed debug of parser states
-o hex|oct : Parse offsets as (h)ex or (o)ctal. Default is hex
-l typenum : Specify link-layer type number. Default is 1 (Ethernet).
See net/bpf.h for list of numbers.
-q : Generate no output at all (automatically turns off -d)
-e l3pid : Prepend dummy Ethernet II header with specified L3PID (in
HEX)
Example: -e 0x800
-i proto : Prepend dummy IP header with specified IP protocol (in
DECIMAL).
Automatically prepends Ethernet header as well.
Example: -i 46
-m max-packet : Max packet length in output, default is 64000
-u srcp,destp : Prepend dummy UDP header with specified dest and source ports
(in DECIMAL).
Automatically prepends Ethernet and IP headers as well
Example: -u 30,40
-T srcp,destp : Prepend dummy TCP header with specified dest and source ports
(in DECIMAL).
Automatically prepends Ethernet and IP headers as well
Example: -T 50,60
-s srcp,dstp,tag: Prepend dummy SCTP header with specified dest/source ports
and verification tag (in DECIMAL).
Automatically prepends Ethernet and IP headers as well
Example: -s 30,40,34
-S srcp,dstp,ppi: Prepend dummy SCTP header with specified dest/source ports
and verification tag 0. It also prepends a dummy SCTP DATA
chunk header with payload protocol identifier ppi.
Example: -S 30,40,34
-t timefmt : Treats the text before the packet as a date/time code; the
specified argument is a format string of the sort supported
by strptime.
Example: The time "10:15:14.5476" has the format code
"%H:%M:%S."
NOTE: The subsecond component delimiter must be specified
(.) but no pattern is required; the remaining number
is assumed to be fractions of a second.
-w <filename>
Write the capture file generated by text2pcap
to <filename>. The default is to write to standard
output.
-h
Display the help message
-d
Displays debugging information during the process. Can be
used multiple times to generate more debugging information.
-q
Be completely quiet during the process.
-o hex|oct
Specify the radix for the offsets (hex or octal). Defaults to
hex. This corresponds to the -A option for od.
-l
Specify the link-layer type of this packet. Default is
Ethernet(1). See net/bpf.h for the complete list of possible
encapsulations. Note that this option should be used if your
dump is a complete hex dump of an encapsulated packet and you
wish to specify the exact type of encapsulation. Example: -l 7
for ARCNet packets.
-e l3pid
Include a dummy Ethernet header before each packet. Specify the
L3PID for the Ethernet header in hex. Use this option if your
dump has Layer 3 header and payload (e.g. IP header), but no
Layer 2 encapsulation. Example: -e 0x806 to specify an ARP
packet.
For IP packets, instead of generating a fake Ethernet header you
can also use -l 12 to indicate a raw IP packet to Wireshark. Note
that -l 12 does not work for any non-IP Layer 3 packet (e.g.
ARP), whereas generating a dummy Ethernet header with -e works
for any sort of L3 packet.
-u srcport destport
Include dummy UDP headers before each packet. Specify the
source and destination UDP ports for the packet in decimal.
Use this option if your dump is the UDP payload of a packet but
does not include any UDP, IP or Ethernet headers. Note that this
automatically includes appropriate Ethernet and IP headers with
each packet. Example: -u 1000 69 to make the packets look like
TFTP/UDP packets.