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=head1 NAME

mergecap - Merges two capture files into one

=head1 SYNOPSYS

B<mergecap>
S<[ B<-hva> ]>
S<[ B<-s> I<snaplen> ]>
S<[ B<-F> I<file format> ]>
S<[ B<-T> I<encapsulation type> ]>
S<B<-w> I<outfile>>
I<infile>
I<...>

=head1 DESCRIPTION

B<Mergecap> is a program that combines multiple saved capture files into
a single output file specified by the B<-w> argument.  B<Mergecap> knows
how to read B<libpcap> capture files, including those of B<tcpdump>,
B<Ethereal>, and other tools that write captures in that format.  In
addition, B<Mergecap> can read capture files from B<snoop> and
B<atmsnoop>, Shomiti/Finisar B<Surveyor> captures, Novell B<LANalyzer>
captures, Network General/Network Associates DOS-based B<Sniffer>
(compressed or uncompressed) captures, Microsoft B<Network Monitor>
captures, files from AIX's B<iptrace>, Cinco Networks B<NetXRay>
captures, captures from Network Associates Windows-based B<Sniffer>, AG
Group/WildPackets B<EtherPeek>/B<TokenPeek>/B<AiroPeek> captures,
captures from B<RADCOM>'s WAN/LAN analyzer, B<Lucent/Ascend> router
debug output, files from HP-UX's B<nettl>, the dump output from
B<Toshiba's> ISDN routers, the output from B<i4btrace> from the ISDN4BSD
project, the output in B<IPLog> format from the Cisco Secure Intrusion
Detection System, B<pppd logs> (pppdump format), the output from VMS's
B<TCPIPtrace>/B<TCPtrace>/B<UCX$TRACE> utilities, the text output from
the B<DBS Etherwatch> VMS utility, traffic capture files from Visual
Networks' Visual UpTime, the output from B<CoSine> L2 debug, the output
from Accellent's 5Views LAN agents, captures in Endace Measurement
Systems' ERF format, Linux Bluez Bluetooth stack B<hcidump -w> traces,
and captures from Network Instruments Observer version 9.  There is no
need to tell B<Mergecap> what type of file you are reading; it will
determine the file type by itself.  B<Mergecap> is also capable of
reading any of these file formats if they are compressed using gzip. 
B<Mergecap> recognizes this directly from the file; the '.gz' extension
is not required for this purpose. 

By default, it writes the capture file in B<libpcap> format, and writes
all of the packets in both input capture files to the output file.  The
B<-F> flag can be used to specify the format in which to write the
capture file; it can write the file in B<libpcap> format (standard
B<libpcap> format, a modified format used by some patched versions of
B<libpcap>, the format used by Red Hat Linux 6.1, or the format used by
SuSE Linux 6.3), B<snoop> format, uncompressed B<Sniffer> format,
Microsoft B<Network Monitor> 1.x format, the format used by
Windows-based versions of the B<Sniffer> software, and the format used
by Visual Networks' software.

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

If the B<-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).

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 B<libpcap>, do not currently support WTAP_ENCAP_PER_PACKET.
This combination will cause the output file creation to fail.

If the B<-T> flag is used to specify a frame 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 files.  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 'B<-T
fddi>' is specified).

=head1 OPTIONS

=over 4

=item -w

Sets the output filename.

=item -F

Sets the file format of the output capture file.

=item -T

Sets the packet encapsulation type of the output capture file.

=item -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 B<-a> is not specified, the contents of the input files
are merged in chronological order based on each frame's timestamp.
Note: when merging, B<mergecap> assumes that packets within a capture
file are already in chronological order.

=item -v

Causes B<mergecap> to print a number of messages while it's working.

=item -s

Sets the snapshot length to use when writing the data.

=item -h

Prints the version and options and exits.

=head1 SEE ALSO

I<tcpdump(8)>, I<pcap(3)>, I<ethereal(1)>, I<editcap(1)>

=head1 NOTES

B<Mergecap> is based heavily upon B<editcap> by Richard Sharpe
<sharpe[AT]ns.aus.com> and Guy Harris <guy[AT]alum.mit.edu>.

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

=head1 AUTHORS

  Original Author
  -------- ------
  Scott Renfro             <scott[AT]renfro.org>


  Contributors
  ------------