mergecap - Merges two or more capture files into one
mergecap [ -hva ] [ -s snaplen ] [ -F file format ] [ -T encapsulation type ] -w outfile|- 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 libpcap capture files, including those of tcpdump, Ethereal, and other tools that write captures in that format.
Mergecap can read / import the following file formats:
There is no need to tell Mergecap what type of file you are reading; it will determine the file type by itself. Mergecap is also capable of reading any of these file formats if they are compressed using gzip. Mergecap recognizes this directly from the file; the '.gz' extension is not required for this purpose.
By default, it writes the capture file in libpcap format, and writes all of the packets in both input capture files 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.
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.
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).
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 libpcap, do not currently support WTAP_ENCAP_PER_PACKET. This combination will cause the output file creation to fail.
If the -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 '-T fddi' is specified).
tcpdump(8), pcap(3), ethereal(1), editcap(1)
Mergecap is based heavily upon editcap by Richard Sharpe <sharpe[AT]ns.aus.com> and Guy Harris <guy[AT]alum.mit.edu>.
Mergecap is part of the Ethereal distribution. The latest version of Ethereal can be found at http://www.ethereal.com.
Original Author -------- ------ Scott Renfro <scott[AT]renfro.org>
Contributors ------------ Bill Guyton <guyton[AT]bguyton.com>