EDITCAP(1) EDITCAP(1)

NAME

editcap - Edit and/or translate the format of capture files

SYNOPSIS

editcap [ -a <frame:comment> ] [ -A <start time> ] [ -B <stop time> ]
[ -c <packets per file> ] [ -C [offset:]<choplen> ]
[ -E <error probability> ] [ -F <file format> ] [ -h ]
[ -i <seconds per file> ] [ -o <change offset> ] [ -L ] [ -r ]
[ -s <snaplen> ] [ -S <strict time adjustment> ]
[ -t <time adjustment> ] [ -T <encapsulation type> ] [ -v ]
[ --inject-secrets <secrets type>,<file> ] [ --discard-all-secrets ]
[ --capture-comment <comment> ] [ --discard-capture-comment ] infile
outfile [ packet#[-packet#] ... ]

editcap -d -D <dup window> -w <dup time window> [ -v ]
[ -I <bytes to ignore> ] [ --skip-radiotap-header ] infile outfile

editcap [ -V ]

DESCRIPTION

Editcap is a program that reads some or all of the captured packets
from the infile, optionally converts them in various ways and writes
the resulting packets to the capture outfile (or outfiles).

By default, it reads all packets from the infile and writes them to
the outfile in pcapng file format.

The -A and -B option allow you to limit the time range from which
packets are read from the infile.

An optional list of packet numbers can be specified on the command
tail; individual packet numbers separated by whitespace and/or ranges
of packet numbers can be specified as start-end, referring to all
packets from start to end. By default the selected packets with
those numbers will not be written to the capture file. If the -r
flag is specified, the whole packet selection is reversed; in that
case only the selected packets will be written to the capture file.

Editcap can also be used to remove duplicate packets. Several
different options (-d, -D and -w) are used to control the packet
window or relative time window to be used for duplicate comparison.

Editcap can be used to assign comment strings to frame numbers.

Editcap is able to detect, read and write the same capture files that
are supported by Wireshark. The input file doesn't need a specific
filename extension; the file format and an optional gzip, zstd or lz4
compression will be automatically detected. Near the beginning of
the DESCRIPTION section of wireshark(1) or
<https://www.wireshark.org/docs/man-pages/wireshark.html> is a
detailed description of the way Wireshark handles this, which is the
same way Editcap handles this.

Editcap can write the file in several output formats. The -F flag can
be used to specify the format in which to write the capture file;
editcap -F provides a list of the available output formats.

OPTIONS

-a <framenum:comment>

For the specified frame number, assign the given comment string.
Can be repeated for multiple frames. Quotes should be used with
comment strings that include spaces.

-A <start time>

Reads only the packets whose timestamp is on or after <start
time>. The time may be given either in ISO 8601 format or in
Unix epoch timestamp format.

ISO 8601 format is either

YYYY-MM-DD HH:MM:SS[.nnnnnnnnn][Z|+-hh:mm]

or

YYYY-MM-DDTHH:MM:SS[.nnnnnnnnn][Z|+-hh:mm]

The fractional seconds are optional, as is the time zone offset
from UTC (in which case local time is assumed).

Unix epoch format is in seconds since the Unix epoch and
nanoseconds, with either a period or a comma separating the
seconds and nanoseconds. The nanoseconds are optional. The Unix
epoch is 1970-01-01 00:00:00 UTC, so this format is not local
time.

-B <stop time>

Reads only the packets whose timestamp is before <stop time>.
The time may be given either in ISO 8601 format or in Unix epoch
timestamp format.

ISO 8601 format is either

YYYY-MM-DD HH:MM:SS[.nnnnnnnnn][Z|+-hh:mm]

or

YYYY-MM-DDTHH:MM:SS[.nnnnnnnnn][Z|+-hh:mm]

The fractional seconds are optional, as is the time zone offset
from UTC (in which case local time is assumed).

Unix epoch format is in seconds since the Unix epoch and
nanoseconds, with either a period or a comma separating the
seconds and nanoseconds. The nanoseconds are optional. The Unix
epoch is 1970-01-01 00:00:00 UTC, so this format is not local
time.

-c <packets per file>

Splits the packet output to different files based on uniform
packet counts with a maximum of <packets per file> each.

Each output file will be created with an infix
_nnnnn[_YYYYmmddHHMMSS] inserted before the file extension (which
may be null) of outfile. The infix consists of the ordinal
number of the output file, starting with 00000, followed by the
timestamp of its first packet. The timestamp is omitted if the
input file does not contain timestamp information.

After the specified number of packets is written to the output
file, the next output file is opened. The default is to use a
single output file. This option conflicts with -i.

-C [offset:]<choplen>

Sets the chop length to use when writing the packet data. Each
packet is chopped by <choplen> bytes of data. Positive values
chop at the packet beginning while negative values chop at the
packet end.

If an optional offset precedes the <choplen>, then the bytes
chopped will be offset from that value. Positive offsets are from
the packet beginning, while negative offsets are from the packet
end.

This is useful for chopping headers for decapsulation of an
entire capture, removing tunneling headers, or in the rare case
that the conversion between two file formats leaves some random
bytes at the end of each packet. Another use is for removing vlan
tags.

Note

This option can be used more than once, effectively allowing
you to chop
bytes from up to two different areas of a packet in a single
pass provided that you specify at least one chop length as a
positive value and at least one as a negative value. All
positive chop lengths are added together as are all negative
chop lengths.

-d

Attempts to remove duplicate packets. The length and MD5 hash of
the current packet are compared to the previous four (4) packets.
If a match is found, the current packet is skipped. This option
is equivalent to using the option -D 5.

-D <dup window>

Attempts to remove duplicate packets. The length and MD5 hash of
the current packet are compared to the previous <dup window> - 1
packets. If a match is found, the current packet is skipped.

The use of the option -D 0 combined with the -v option is useful
in that each packet's Packet number, Len and MD5 Hash will be
printed to standard out. This verbose output (specifically the
MD5 hash strings) can be useful in scripts to identify duplicate
packets across trace files.

The <dup window> is specified as an integer value between 0 and
1000000 (inclusive).

Note

Specifying large <dup window> values with large tracefiles
can
result in very long processing times for editcap.

-E <error probability>

Sets the probability that bytes in the output file are randomly
changed. Editcap uses that probability (between 0.0 and 1.0
inclusive) to apply errors to each data byte in the file. For
instance, a probability of 0.02 means that each byte has a 2%
chance of having an error.

This option is meant to be used for fuzz-testing protocol
dissectors.

-F <file format>

Sets the file format of the output capture file. Editcap can
write the file in several formats, editcap -F provides a list of
the available output formats. The default is the pcapng format.

-h

Prints the version and options and exits.

-i <seconds per file>

Splits the packet output to different files based on uniform time
intervals using a maximum interval of <seconds per file> each.
Floating point values (e.g. 0.5) are allowed.

Each output file will be created with an infix
_nnnnn[_YYYYmmddHHMMSS] inserted before the file extension (which
may be null) of outfile. The infix consists of the ordinal
number of the output file, starting with 00000, followed by the
timestamp of its first packet. The timestamp is omitted if the
input file does not contain timestamp information.

After packets for the specified time interval are written to the
output file, the next output file is opened. The default is to
use a single output file. This option conflicts with -c.

-I <bytes to ignore>

Ignore the specified number of bytes at the beginning of the
frame during MD5 hash calculation, unless the frame is too short,
then the full frame is used. Useful to remove duplicated packets
taken on several routers (different mac addresses for example)
e.g. -I 26 in case of Ether/IP will ignore ether(14) and IP
header(20 - 4(src ip) - 4(dst ip)). The default value is 0.

-L

Adjust the original frame length accordingly when chopping and/or
snapping (in addition to the captured length, which is always
adjusted regardless of whether -L is specified or not). See also
-C <choplen> and -s <snaplen>.

-o <change offset>

When used in conjunction with -E, skip some bytes from the
beginning of the packet from being changed. In this way some
headers don't get changed, and the fuzzer is more focused on a
smaller part of the packet. Keeping a part of the packet fixed
the same dissector is triggered, that make the fuzzing more
precise.

-r

Reverse the packet selection. Causes the packets whose packet
numbers are specified on the command line to be written to the
output capture file, instead of discarding them.

-s <snaplen>

Sets the snapshot length to use when writing the data. If the -s
flag is used to specify a snapshot length, packets in the input
file with more captured data than the specified snapshot length
will have only the amount of data specified by the snapshot
length written to the output file.

This may be useful if the program that is to read the output file
cannot handle packets larger than a certain size (for example,
the versions of snoop in Solaris 2.5.1 and Solaris 2.6 appear to
reject Ethernet packets larger than the standard Ethernet MTU,
making them incapable of handling gigabit Ethernet captures if
jumbo packets were used).

--seed <seed>

When used in conjunction with -E, set the seed for the
pseudo-random number generator. This is useful for recreating a
particular sequence of errors.

--skip-radiotap-header

Skip the radiotap header of each frame when checking for packet
duplicates. This is useful when processing a capture created by
combining outputs of multiple capture devices on the same channel
in the vicinity of each other.

-S <strict time adjustment>

Time adjust selected packets to ensure strict chronological
order.

The <strict time adjustment> value represents relative seconds
specified as seconds[.fractional seconds].

As the capture file is processed each packet's absolute time is
possibly adjusted to be equal to or greater than the previous
packet's absolute timestamp depending on the <strict time
adjustment> value.

If <strict time adjustment> value is 0 or greater (e.g. 0.000001)
then only packets with a timestamp less than the previous packet
will adjusted. The adjusted timestamp value will be set to be
equal to the timestamp value of the previous packet plus the
value of the <strict time adjustment> value. A <strict time
adjustment> value of 0 will adjust the minimum number of
timestamp values necessary to ensure that the resulting capture
file is in strict chronological order.

If <strict time adjustment> value is specified as a negative
value, then the timestamp values of all packets will be adjusted
to be equal to the timestamp value of the previous packet plus
the absolute value of the <strict time adjustment> value. A
<strict time adjustment> value of -0 will result in all packets
having the timestamp value of the first packet.

This feature is useful when the trace file has an occasional
packet with a negative delta time relative to the previous
packet.

-t <time adjustment>

Sets the time adjustment to use on selected packets. If the -t
flag is used to specify a time adjustment, the specified
adjustment will be applied to all selected packets in the capture
file. The adjustment is specified as seconds[.fractional
seconds]. For example, -t 3600 advances the timestamp on
selected packets by one hour while -t -0.5 reduces the timestamp
on selected packets by one-half second.

This feature is useful when synchronizing dumps collected on
different machines where the time difference between the two
machines is known or can be estimated.

-T <encapsulation type>

Sets the packet encapsulation type of the output capture file.
If the -T flag is used to specify an encapsulation type, the
encapsulation type of the output capture file will be forced to
the specified type. editcap -T provides a list of the available
types. The default type is the one appropriate to the
encapsulation type of the input capture file.

Note: this merely forces the encapsulation type of the output
file to be the specified type; the packet headers of the packets
will not be translated from the encapsulation type of the input
capture file to the specified encapsulation type (for example, it
will not translate an Ethernet capture to an FDDI capture if an
Ethernet capture is read and '-T fddi' is specified). If you need
to remove/add headers from/to a packet, you will need
od(1)/text2pcap(1).

-v

Causes editcap to print verbose messages while it's working.

Use of -v with the de-duplication switches of -d, -D or -w will
cause all MD5 hashes to be printed whether the packet is skipped
or not.

-V

Print the version and exit.

-w <dup time window>

Attempts to remove duplicate packets. The current packet's
arrival time is compared with up to 1000000 previous packets. If
the packet's relative arrival time is less than or equal to the
<dup time window> of a previous packet and the packet length and
MD5 hash of the current packet are the same then the packet to
skipped. The duplicate comparison test stops when the current
packet's relative arrival time is greater than <dup time window>.

The <dup time window> is specified as seconds[.fractional
seconds].

The [.fractional seconds] component can be specified to nine (9)
decimal places (billionths of a second) but most typical trace
files have resolution to six (6) decimal places (millionths of a
second).

Note

Specifying large <dup time window> values with large
tracefiles can
result in very long processing times for editcap.

Note

The -w option assumes that the packets are in chronological
order.
If the packets are NOT in chronological order then the -w
duplication removal option may not identify some duplicates.

--inject-secrets <secrets type>,<file>

Inserts the contents of <file> into a Decryption Secrets Block
(DSB) within the pcapng output file. This enables decryption
without requiring additional configuration in protocol
preferences.

The file format is described by <secrets type> which can be one
of:

tls TLS Key Log as described at
<https://developer.mozilla.org/NSS_Key_Log_Format> wg WireGuard
Key Log, see
<https://gitlab.com/wireshark/wireshark/-/wikis/WireGuard#key-log-format>

This option may be specified multiple times. The available
options for <secrets type> can be listed with --inject-secrets
help.

--discard-all-secrets

Discard all decryption secrets from the input file when writing
the output file. Does not discard secrets added by
--inject-secrets in the same command line.

--capture-comment <comment>

Adds the given comment to the output file, if supported by the
output file format. New comments will be added after any
comments present in the input file unless
--discard-capture-comment is also specified.

This option may be specified multiple times. Note that Wireshark
currently only displays the first comment of a capture file.

--discard-capture-comment

Discard all capture file comments from the input file when
writing the output file. Does not discard comments added by
--capture-comment in the same command line.

EXAMPLES

To see more detailed description of the options use:

editcap -h

To shrink the capture file by truncating the packets at 64 bytes and
writing it as Sun snoop file use:

editcap -s 64 -F snoop capture.pcapng shortcapture.snoop

To delete packet 1000 from the capture file use:

editcap capture.pcapng sans1000.pcapng 1000

To limit a capture file to packets from number 200 to 750 (inclusive)
use:

editcap -r capture.pcapng small.pcapng 200-750

To get all packets from number 1-500 (inclusive) use:

editcap -r capture.pcapng first500.pcapng 1-500

or

editcap capture.pcapng first500.pcapng 501-9999999

To exclude packets 1, 5, 10 to 20 and 30 to 40 from the new file use:

editcap capture.pcapng exclude.pcapng 1 5 10-20 30-40

To select just packets 1, 5, 10 to 20 and 30 to 40 for the new file
use:

editcap -r capture.pcapng select.pcapng 1 5 10-20 30-40

To remove duplicate packets seen within the prior four frames use:

editcap -d capture.pcapng dedup.pcapng

To remove duplicate packets seen within the prior four frames while
skipping radiotap headers use:

editcap -d --skip-radiotap-header capture.pcapng dedup.pcapng

To remove duplicate packets seen within the prior 100 frames use:

editcap -D 101 capture.pcapng dedup.pcapng

To remove duplicate packets seen equal to or less than 1/10th of a
second:

editcap -w 0.1 capture.pcapng dedup.pcapng

To display the MD5 hash for all of the packets (and NOT generate any
real output file):

editcap -v -D 0 capture.pcapng /dev/null

or on Windows systems

editcap -v -D 0 capture.pcapng NUL

To advance the timestamps of each packet forward by 3.0827 seconds:

editcap -t 3.0827 capture.pcapng adjusted.pcapng

To ensure all timestamps are in strict chronological order:

editcap -S 0 capture.pcapng adjusted.pcapng

To introduce 5% random errors in a capture file use:

editcap -E 0.05 capture.pcapng capture_error.pcapng

To remove vlan tags from all packets within an Ethernet-encapsulated
capture file, use:

editcap -L -C 12:4 capture_vlan.pcapng capture_no_vlan.pcapng

To chop both the 10 byte and 20 byte regions from the following 75
byte packet in a single pass, use any of the 8 possible methods
provided below:

<--------------------------- 75 ---------------------------->

+---+-------+-----------+---------------+-------------------+
| 5 | 10 | 15 | 20 | 25 |
+---+-------+-----------+---------------+-------------------+

1) editcap -C 5:10 -C -25:-20 capture.pcapng chopped.pcapng
2) editcap -C 5:10 -C 50:-20 capture.pcapng chopped.pcapng
3) editcap -C -70:10 -C -25:-20 capture.pcapng chopped.pcapng
4) editcap -C -70:10 -C 50:-20 capture.pcapng chopped.pcapng
5) editcap -C 30:20 -C -60:-10 capture.pcapng chopped.pcapng
6) editcap -C 30:20 -C 15:-10 capture.pcapng chopped.pcapng
7) editcap -C -45:20 -C -60:-10 capture.pcapng chopped.pcapng
8) editcap -C -45:20 -C 15:-10 capture.pcapng chopped.pcapng

To add comment strings to the first 2 input frames, use:

editcap -a "1:1st frame" -a 2:Second capture.pcapng capture-comments.pcapng

SEE ALSO

pcap(3), wireshark(1), tshark(1), mergecap(1), dumpcap(1),
capinfos(1), text2pcap(1), reordercap(1), od(1), pcap-filter(7) or
tcpdump(8)

NOTES

This is the manual page for Editcap 3.6.22. Editcap is part of the
Wireshark distribution. The latest version of Wireshark can be found
at <https://www.wireshark.org>.

HTML versions of the Wireshark project man pages are available at
<https://www.wireshark.org/docs/man-pages>.

AUTHORS

Original Author
Richard Sharpe <sharpe[AT]ns.aus.com>

Contributors
Guy Harris <guy[AT]alum.mit.edu>
Ulf Lamping <ulf.lamping[AT]web.de>

2024-03-27 EDITCAP(1)