User Guide

Related command line tools
235
D.9. text2pcap: 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 -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 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. Possibilities include inserting headers such as Ethernet, Ethernet + IP,
Ethernet + IP + UDP, or Ethernet + Ip + TCP before each packet. This allows Wireshark or any other full-
packet decoder to handle these dumps.