EDITCAP(1) The Ethereal Network Analyzer EDITCAP(1)
editcap - Edit and/or translate the format of capture files
editcap [ -F file format ] [ -T encapsulation type ] [ -r ] [ -v ] [ -s snaplen ]
[ -t time adjustment ] [ -h ] infile outfile [ record# ... ]
Editcap is a program that reads a saved capture file and writes some or all of the packets
in that capture file to another capture file. Editcap knows how to read libpcap capture
files, including those of tcpdump, Ethereal, and other tools that write captures in that
format. In addition, Editcap can read capture files from snoop and atmsnoop, Shomiti/Fin-
isar Surveyor, Novell LANalyzer, Network General/Network Associates DOS-based Sniffer
(compressed or uncompressed), Microsoft Network Monitor, AIX's iptrace, Cinco Networks
NetXRay, Network Associates Windows-based Sniffer, AG Group/WildPackets EtherPeek/Token-
Peek/AiroPeek, RADCOM's WAN/LAN analyzer, Lucent/Ascend router debug output, HP-UX's
nettl, the dump output from Toshiba's ISDN routers, the output from i4btrace from the
ISDN4BSD project, the output in IPLog format from the Cisco Secure Intrusion Detection
System, pppd logs (pppdump format), the output from VMS's TCPIPtrace utility, the text
output from the DBS Etherwatch VMS utility, traffic capture files from Visual Networks'
Visual UpTime and the output from CoSine L2 debug. There is no need to tell Editcap what
type of file you are reading; it will determine the file type by itself. Editcap is also
capable of reading any of these file formats if they are compressed using gzip. Editcap
recognizes this directly from the file; the '.gz' extension is not required for this pur-
By default, it writes the capture file in libpcap format, and writes all of the packets in
the capture file to the output file. The -F flag can be used to specify the format in
which to write the capture file; it can write the file in libpcap format (standard libpcap
format, a modified format used by some patched versions of libpcap, the format used by Red
Hat Linux 6.1, or the format used by SuSE Linux 6.3), snoop format, uncompressed Sniffer
format, Microsoft Network Monitor 1.x format, the format used by Windows-based versions of
the Sniffer software, and the format used by Visual Networks' software.
A list of packet numbers can be specified on the command line; the packets with those num-
bers will not be written to the capture file, unless the -r flag is specified, in which
case only those packets will be written to the capture file. Ranges of packet numbers can
be specified as start-end, referring to all packets from start to end (removing them all
if -r isn't specified, including them all if -r is specified).
If the -s flag is used to specify a snapshot length, frames in the input file with more
captured data than the specified snapshot length will have only the amount of data speci-
fied 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
frames larger than the standard Ethernet MTU, making them incapable of handling gigabit
Ethernet captures if jumbo frames were used).
If the -t flag is used to specify a time adjustment, the specified adjustment will be
applied to all selected frames in the capture file. The adjustment is specified as
[-]seconds[.fractional seconds]. For example, -t 3600 advances the timestamp on selected
frames by one hour while -t -0.5 reduces the timestamp on selected frames by one-half sec-
ond. 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.
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, rather than being the type
appropriate to the encapsulation type of the input capture file. Note that 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 speci-
-F Sets the file format of the output capture file.
-T Sets the packet encapsulation type of the output capture file.
-r Causes the packets whose packet numbers are specified on the command line to be writ-
ten to the output capture file, and no other packets to be written to the output cap-
-v Causes editcap to print a number of messages while it's working.
-s Sets the snapshot length to use when writing the data.
-t Sets the time adjustment to use on selected frames.
-h Prints the version and options and exits.
tcpdump(8), pcap(3), ethereal(1), mergecap(1)
Editcap is part of the Ethereal distribution. The latest version of Ethereal can be found
Richard Sharpe <email@example.com>
Guy Harris <firstname.lastname@example.org>
0.9.8 2002-08-08 EDITCAP(1)