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mergecap(1)             The Wireshark Network Analyzer             mergecap(1)


       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 and pcapng capture files, including those of tcpdump,
       Wireshark and other tools that write captures in those formats.

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

       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.  By default this is the pcapng format.

       -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:

               none: No merging of IDBs is performed, and instead all IDBs are
               copied to the merged output file.

               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.

               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 into a third capture file, in which
       the last packet of one file arrives 100 seconds before the first packet
       of another file, use the following sequence of commands.

       First, use:

           capinfos -aeS a.pcap b.pcap

       to determine the start and end times of the two capture files, as
       seconds since January 1, 1970, 00:00:00 UTC.

       If a.pcap starts at 1009932757 and b.pcap ends at 873660281, then the
       time adjustment to b.pcap that would make it end 100 seconds before
       a.pcap begins would be 1009932757 - 873660281 - 100 = 136272376

       Thus, the next step would be to use:

           editcap -t 136272376 b.pcap b-shifted.pcap

       to generate a version of b.pcap with its time stamps shifted 136272376

       Then the final step would be to use :

           mergecap -w compare.pcap a.pcap b-shifted.pcap

       to merge a.pcap and the shifted b.pcap into compare.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]>

3.4.7                             2021-07-14                       mergecap(1)

wireshark 3.4.7 - Generated Wed Jul 21 07:43:22 CDT 2021
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