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 pcap or pcapng 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, UDP, TCP or SCTP
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 -A x -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 packet, each new
packet starts with an offset of 0 and there is a space separating the offset
from the following bytes. 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. Packets may be preceded by a timestamp. These
are interpreted according to the format given on the command line. If not, the
first packet is timestamped with the current time the conversion takes place.
Multiple packets are written with timestamps differing by one microsecond 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. Possibilities include
inserting headers such as Ethernet, Ethernet + IP, Ethernet + IP + UDP, or TCP,
or SCTP before each packet. This allows Wireshark or any other full-packet
decoder to handle these dumps.
For more information on text2pcap consult your local manual page (man
text2pcap) or the online
version.
Help information available from text2pcap.
Text2pcap (Wireshark) 3.5.0 (v3.5.0rc0-461-g969c1c0271bf)
Generate a capture file from an ASCII hexdump of packets.
See https://www.wireshark.org for more information.
Usage: text2pcap [options] <infile> <outfile>
where <infile> specifies input filename (use - for standard input)
<outfile> specifies output filename (use - for standard output)
Input:
-o hex|oct|dec parse offsets as (h)ex, (o)ctal or (d)ecimal;
default is hex.
-t <timefmt> treat 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
given, but no pattern is required; the remaining
number is assumed to be fractions of a second.
NOTE: Date/time fields from the current date/time are
used as the default for unspecified fields.
-D the text before the packet starts with an I or an O,
indicating that the packet is inbound or outbound.
This is used when generating dummy headers.
The indication is only stored if the output format is pcapng.
-a enable ASCII text dump identification.
The start of the ASCII text dump can be identified
and excluded from the packet data, even if it looks
like a HEX dump.
NOTE: Do not enable it if the input file does not
contain the ASCII text dump.
Output:
-l <typenum> link-layer type number; default is 1 (Ethernet). See
https://www.tcpdump.org/linktypes.html for a list of
numbers. Use this option 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.
-m <max-packet> max packet length in output; default is 262144
-n use pcapng instead of pcap as output format.
-N <intf-name> assign name to the interface in the pcapng file.
Prepend dummy header:
-e <l3pid> prepend dummy Ethernet II header with specified L3PID
(in HEX).
Example: -e 0x806 to specify an ARP packet.
-i <proto> prepend dummy IP header with specified IP protocol
(in DECIMAL).
Automatically prepends Ethernet header as well.
Example: -i 46
-4 <srcip>,<destip> prepend dummy IPv4 header with specified
dest and source address.
Example: -4 10.0.0.1,10.0.0.2
-6 <srcip>,<destip> prepend dummy IPv6 header with specified
dest and source address.
Example: -6 fe80::202:b3ff:fe1e:8329,2001:0db8:85a3::8a2e:0370:7334
-u <srcp>,<destp> prepend dummy UDP header with specified
source and destination ports (in DECIMAL).
Automatically prepends Ethernet & IP headers as well.
Example: -u 1000,69 to make the packets look like
TFTP/UDP packets.
-T <srcp>,<destp> prepend dummy TCP header with specified
source and destination ports (in DECIMAL).
Automatically prepends Ethernet & IP headers as well.
Example: -T 50,60
-s <srcp>,<dstp>,<tag> prepend dummy SCTP header with specified
source/dest ports and verification tag (in DECIMAL).
Automatically prepends Ethernet & IP headers as well.
Example: -s 30,40,34
-S <srcp>,<dstp>,<ppi> prepend dummy SCTP header with specified
source/dest ports and verification tag 0.
Automatically prepends a dummy SCTP DATA
chunk header with payload protocol identifier ppi.
Example: -S 30,40,34
Miscellaneous:
-h display this help and exit.
-v print version information and exit.
-d show detailed debug of parser states.
-q generate no output at all (automatically disables -d).