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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 having their own code  to  read  savefiles.
       If,  in the future, a new file format is supported by libpcap, applica‐
       tions 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 libp‐
       cap 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 oppo‐
       site 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  giv‐
       ing  the	 approximate time the packet was captured; the time stamp con‐
       sists 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 giv‐
       ing  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(3), pcap-linktype(7)

				21 October 2008		      PCAP-SAVEFILE(5)
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