text2pcap - Generate a capture file from an ASCII hexdump of packets

text2pcap [ -h ] [ -d ] [ -q ] [ -o hex|oct ] [ -l <typenum> ] [ -e <l3pid> ] [ -i <proto> ] [ -m <max-packet> ] [ -u <srcport>,<destport> ] [ -T <srcport>,<destport> ] [ -s <srcport>,<destport>,<tag> ] [ -S <srcport>,<destport>,<ppi> ] [ -t <timefmt> ] <infile>|- <outfile>|-

Text2pcap is a program that reads in an ASCII hex dump and writes the data described into a libpcap 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, 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 -Ax -tx1. 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/TCP headers before each packet. This allows Ethereal or any other full-packet decoder to handle these dumps.

-h

Displays a 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 CW-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 Ethereal. 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.

-i <proto>

Include dummy IP headers before each packet. Specify the IP protocol for the packet in decimal. Use this option if your dump is the payload of an IP packet (i.e. has complete L4 information) but does not have an IP header. Note that this automatically includes an appropriate Ethernet header as well. Example: -i 46 to specify an RSVP packet (IP protocol 46).

-m <max-packet>

Set the maximum packet length, default is 64000. Useful for testing various packet boundaries when only an application level datastream is available. Example: od -Ax -tx1 stream | text2pcap -m1460 -T1234,1234 - stream.pcap will convert from plain datastream format to a sequence of Ethernet TCP packets.

-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.

-T <srcport>,<destport>

Include dummy TCP headers before each packet. Specify the source and destination TCP ports for the packet in decimal. Use this option if your dump is the TCP payload of a packet but does not include any TCP, IP or Ethernet headers. Note that this automatically includes appropriate Ethernet and IP headers with each packet. Sequence numbers will start a 0.

-s <srcport>,<destport>,<tag>

Include dummy SCTP headers before each packet. Specify, in decimal, the source and destination SCTP ports, and verification tag, for the packet. Use this option if your dump is the SCTP payload of a packet but does not include any SCTP, IP or Ethernet headers. Note that this automatically includes appropriate Ethernet and IP headers with each packet. A CRC32C checksum will be put into the SCTP header.

-S <srcport>,<destport>,<ppi>

Include dummy SCTP headers before each packet. Specify, in decimal, the source and destination SCTP ports, and a verification tag of 0, for the packet, and prepend a dummy SCTP DATA chunk header with a payload protocol identifier if ppi. Use this option if your dump is the SCTP payload of a packet but does not include any SCTP, IP or Ethernet headers. Note that this automatically includes appropriate Ethernet and IP headers with each packet. A CRC32C checksum will be put into the SCTP header.

-t <timefmt>

Treats the text before the packet as a date/time code; timefmt is a format string of the sort supported by BIstrptime(3). 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.

od(1), tcpdump(8), pcap(3), ethereal(1), editcap(1), strptime(3).

Text2pcap is part of the Ethereal distribution. The latest version of Ethereal can be found at http://www.ethereal.com.

  Ashok Narayanan          <ashokn[AT]cisco.com>