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PCAP-SAVEFILE(5@)                                                                          PCAP-SAVEFILE(5@)



NAME
       pcap-savefile - libpcap savefile format

DESCRIPTION
       NOTE: applications and libraries should, if possible, use libpcap to read savefiles, rather than hav-ing having
       ing their own code to read savefiles.  If, in the future, a new file format is supported by  libpcap,
       applications  and  libraries  using  libpcap to read savefiles will be able to read the new format of
       savefiles, but applications and libraries using their own code to read  savefiles  will  have  to  be
       changed to support the new file format.

       ``Savefiles''  read  and  written  by  libpcap  and  applications using libpcap start with a per-file
       header.  The format of the per-file header is:

              +------------------------------+
              |        Magic number          |
              +--------------+---------------+
              |Major version | Minor version |
              +--------------+---------------+
              |      Time zone offset        |
              +------------------------------+
              |     Time stamp accuracy      |
              +------------------------------+
              |       Snapshot length        |
              +------------------------------+
              |   Link-layer header type     |
              +------------------------------+
       All fields in the per-file header are in the byte order of the host  writing  the  file.   The  first
       field  in the per-file header is a 4-byte magic number, with the value 0xa1b2c3d4.  The magic number,
       when read by a host with the same byte order as the host that wrote the file,  will  have  the  value
       0xa1b2c3d4,  and,  when  read by a host with the opposite byte order as the host that wrote the file,
       will have the value 0xd4c3b2a1.  That allows software reading the file to determine whether the  byte
       order  of the host that wrote the file is the same as the byte order of the host on which the file is
       being read, and thus whether the values in the per-file and  per-packet  headers  need  to  be  byte-swapped. byteswapped.
       swapped.

       Following this are:

              A 2-byte file format major version number; the current version number is 2.

              A 2-byte file format minor version number; the current version number is 4.

              A 4-byte time zone offset; this is always 0.

              A 4-byte number giving the accuracy of time stamps in the file; this is always 0.

              A  4-byte number giving the "snapshot length" of the capture; packets longer than the snapshot
              length are truncated to the snapshot length, so that, if the snapshot length is  N,  only  the
              first N bytes of a packet longer than N bytes will be saved in the capture.

              a  4-byte  number giving the link-layer header type for packets in the capture; see pcap-link-type(7) pcap-linktype(7)
              type(7) for the LINKTYPE_ values that can appear in this field.

       Following the per-file header are zero or more packets; each packet begins with a per-packet  header,
       which is immediately followed by the raw packet data.  The format of the per-packet header is:

              +---------------------------------------+
              |      Time stamp, seconds value        |
              +---------------------------------------+
              |    Time stamp, microseconds value     |
              +---------------------------------------+
              |    Length of captured packet data     |
              +---------------------------------------+
              |Un-truncated length of the packet data |
              +---------------------------------------+
       All  fields  in  the  per-packet header are in the byte order of the host writing the file.  The per-packet perpacket
       packet header begins with a time stamp giving the approximate time the packet was captured; the  time
       stamp  consists  of  a  4-byte value, giving the time in seconds since January 1, 1970, 00:00:00 UTC,
       followed by a 4-byte value, giving the time in microseconds since that second.  Following that are  a
       4-byte  value  giving  the  number  of bytes of captured data that follow the per-packet header and a
       4-byte value giving the number of bytes that would have been present had the packet  not  been  trun-cated truncated
       cated  by  the  snapshot length.  The two lengths will be equal if the number of bytes of packet data
       are less than or equal to the snapshot length.

SEE ALSO
       pcap(3PCAP), pcap-linktype(7)



                                               21 October 2008                             PCAP-SAVEFILE(5@)