Provided by: libpcap0.8-dev_1.1.1-10_amd64 bug

NAME

       pcap-savefile - libpcap savefile format

DESCRIPTION

       NOTE:  applications  and  libraries  should,  if  possible, use libpcap to read savefiles,
       rather than having 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.

       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-linktype(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 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 truncated 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)