mergecap - Merges two or more capture files into one


   mergecap [ -a ] [ -F <file format> ] [ -h ] [ -I <IDB merge mode> ]
   [ -s <snaplen> ] [ -v ] [ -V ] -w <outfile>|- <infile> [<infile> ...]


   Mergecap is a program that combines multiple saved capture files into a
   single output file specified by the -w argument.  Mergecap knows how to
   read pcap capture files, including those of tcpdump, Wireshark, and
   other tools that write captures in that format.

   By default, Mergecap writes the capture file in pcap format, and writes
   all of the packets from the input capture files to the output file.

   Mergecap is able to detect, read and write the same capture files that
   are supported by Wireshark.  The input files don't need a specific
   filename extension; the file format and an optional gzip compression
   will be automatically detected.  Near the beginning of the DESCRIPTION
   section of wireshark(1) or
   <> is a detailed
   description of the way Wireshark handles this, which is the same way
   Mergecap handles this.

   Mergecap 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,
   mergecap -F provides a list of the available output formats.

   Packets from the input files are merged in chronological order based on
   each frame's timestamp, unless the -a flag is specified.  Mergecap
   assumes that frames within a single capture file are already stored in
   chronological order.  When the -a flag is specified, packets are copied
   directly from each input file to the output file, independent of each
   frame's timestamp.

   The output file frame encapsulation type is set to the type of the
   input files if all input files have the same type.  If not all of the
   input files have the same frame encapsulation type, the output file
   type is set to WTAP_ENCAP_PER_PACKET.  Note that some capture file
   formats, most notably pcap, do not currently support
   WTAP_ENCAP_PER_PACKET.  This combination will cause the output file
   creation to fail.


   -a  Causes the frame timestamps to be ignored, writing all packets from
       the first input file followed by all packets from the second input
       file.  By default, when -a is not specified, the contents of the
       input files are merged in chronological order based on each frame's

       Note: when merging, mergecap assumes that packets within a capture
       file are already in chronological order.

   -F  <file format>
       Sets the file format of the output capture file. Mergecap can write
       the file in several formats; mergecap -F provides a list of the
       available output formats. The default is to use the file format of
       the first input file.

   -h  Prints the version and options and exits.

   -I  <IDB merge mode>
       Sets the Interface Description Block (IDB) merge mode to use during
       merging.  mergecap -I provides a list of the available IDB merge

       Every input file has one or more IDBs, which describe the
       interface(s) the capture was performed on originally. This includes
       encapsulation type, interface name, etc. When mergecap merges
       multiple input files, it has to merge these IDBs somehow for the
       new merged output file. This flag controls how that is
       accomplished. The currently available modes are:

        * 'B<none>': no merging of IDBs is performed, and instead all IDBs are
                     copied to the merged output file.
        * 'B<all>':  IDBs are merged only if all input files have the same number
                     of IDBs, and each IDB matches their respective entry in the
                     other files. This is the default mode.
        * 'B<any>':  Any and all duplicate IDBs are merged into one IDB, regardless
                     of what file they are in.

       Note that an IDB is only considered a matching duplicate if it has
       the same encapsulation type, name, speed, time precision, comments,
       description, etc.

   -s  <snaplen>
       Sets the snapshot length to use when writing the data.  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 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 frames larger than the
       standard Ethernet MTU, making them incapable of handling gigabit
       Ethernet captures if jumbo frames were used).

   -v  Causes mergecap to print a number of messages while it's working.

   -V  Print the version and exit.

   -w  <outfile>|-
       Sets the output filename. If the name is '-', stdout will be used.
       This setting is mandatory.


   To merge two capture files together, 100 seconds apart use:

       capinfos -aeS a.pcap b.pcap

   (Let's suppose a.pcap starts at 1009932757 and b.pcap ends at
   873660281. 1009932757 - 873660281 - 100 = 136272376 seconds.)

       editcap -t 136272376 b.pcap b-shifted.pcap
       mergecap -w compare.pcap a.pcap b-shifted.pcap


   pcap(3), wireshark(1), tshark(1), dumpcap(1), editcap(1), text2pcap(1),
   pcap-filter(7) or tcpdump(8)


   Mergecap is based heavily upon editcap by Richard Sharpe
   <sharpe[AT]> and Guy Harris <guy[AT]>.

   Mergecap is part of the Wireshark distribution.  The latest version of
   Wireshark can be found at <>.

   HTML versions of the Wireshark project man pages are available at:


     Original Author
     -------- ------
     Scott Renfro             <scott[AT]>

     Bill Guyton              <guyton[AT]>


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